ORCID Profile
0000-0002-8991-1921
Current Organisation
University of Oxford
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Publisher: Royal Society of Chemistry (RSC)
Date: 1995
DOI: 10.1039/CS9952400329
Publisher: Royal Society of Chemistry (RSC)
Date: 2006
DOI: 10.1039/B510616H
Abstract: The synthesis, characterisation and thermal and photochemical reactivity of Ru(CO)2(PPh3)(dppe) 1 towards hydrogen are described. Compound proved to exist in both fac (major) and mer forms in solution. Under thermal conditions, PPh3 is lost from 1 in the major reaction pathway and the known complex Ru(CO)2(dppe)(H)2 2 is formed. Photochemically, CO loss is the dominant process, leading to the alternative dihydride Ru(CO)(PPh3)(dppe)(H)2 3. The major isomer of 3, viz. 3a, contains hydride ligands that are trans to CO and trans to one of the phosphorus atoms of the dppe ligand but a second isomer, 3b, where both hydride ligands are trans to distinct phosphines, is also formed. On the NMR timescale, no interconversion of 3a and 3b was observed, although hydride site interchange is evident with activation parameters of DeltaH(double dagger) = 95 +/- 6 kJ mol(-1) and DeltaS(double dagger) = 26 +/- 17 J K(-1) mol(-1). Density functional theory confirms that the observed species are the most stable isomeric forms, and suggests that hydride exchange occurs via a transition state featuring an eta2-coordinated H2 unit.
Publisher: American Chemical Society (ACS)
Date: 03-01-2004
DOI: 10.1021/OM034229+
Publisher: Royal Society of Chemistry (RSC)
Date: 12-12-2002
DOI: 10.1039/B208530E
Publisher: Royal Society of Chemistry (RSC)
Date: 2009
DOI: 10.1039/B912487J
Publisher: American Chemical Society (ACS)
Date: 25-07-2011
DOI: 10.1021/JA2028475
Abstract: In the field of molecular electronics, an intimate link between the delocalization of molecular orbitals and their ability to support current flow is often assumed. Delocalization, in turn, is generally regarded as being synonymous with structural symmetry, for ex le, in the lengths of the bonds along a molecular wire. In this work, we use density functional theory in combination with nonequilibrium Green's functions to show that precisely the opposite is true in the extended metal atom chain Cr(3)(dpa)(4)(NCS)(2) where the delocalized π framework has previously been proposed to be the dominant conduction pathway. Low-symmetry distortions of the Cr(3) core do indeed reduce the effectiveness of these π channels, but this is largely irrelevant to electron transport at low bias simply because they lie far below the Fermi level. Instead, the dominant pathway is through higher-lying orbitals of σ symmetry, which remain essentially unperturbed by even quite substantial distortions. In fact, the conductance is actually increased marginally because the σ(nb) channel is displaced upward toward the Fermi level. These calculations indicate a subtle and counterintuitive relationship between structure and function in these metal chains that has important implications for the interpretation of data emerging from scanning tunnelling and atomic force microscopy experiments.
Publisher: American Chemical Society (ACS)
Date: 28-03-2002
DOI: 10.1021/JA012630M
Abstract: photoelectron-photoion coincidence spectroscopy and density functional theory calculations have been used to investigate the dissociation kinetics of the benzene chromium tricarbonyl ion, BzCr(CO)3+ (Bz = C6H6). The dissociation of the BzCr(CO)3+ ion proceeds by the sequential loss of three CO and benzene ligands. The first and third CO and the benzene loss reactions were associated with metastable precursor ions (lifetimes in the microsecond range). By simulating the resulting asymmetric time-of-flight peak shapes and breakdown diagram, the 0 K appearance energies of the four product ions were determined to be 8.33 +/- 0.05, 8.93 +/- 0.05, 9.97 +/- 0.06, and 11.71 +/- 0.06 eV, respectively. Combined with the ionization energy of BzCr(CO)3, 7.30 +/- 0.05 eV, the three successive Cr-CO bond energies in the BzCr(CO)3+ were found to alternate, with values of 1.03 +/- 0.05, 0.60 +/- 0.05, and 1.04 +/- 0.05 eV, respectively, and the Bz-Cr bond energy in BzCr+ is 1.74 +/- 0.05 eV, a trend confirmed by the density functional theory (DFT) calculations. Using the heats of formation of the fully dissociated products, C6H6, Cr+, and CO, the 298 K heats of formation the ionic BzCr(CO)n+ (n = 03) species were determined. By scaling the DFT calculated bond energies for the neutral molecules, the heats of formation of the neutral BzCr(CO)n (n = 03) were also obtained.
Publisher: Wiley
Date: 05-12-2017
Abstract: One-electron reduction of a pyrazolate-bridged triangular Fe
Publisher: Elsevier BV
Date: 11-2005
Publisher: Elsevier BV
Date: 09-2002
Publisher: American Chemical Society (ACS)
Date: 08-1994
DOI: 10.1021/IC00096A024
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7DT02930F
Abstract: The distribution of Fe( ii ) and Ni( ii ) over two distinct metal sites in [Fe 9−x Ni x ] clusters is studied by X-ray crystallography, Mössbauer and XRF spectroscopies, and DFT calculations.
Publisher: Royal Society of Chemistry (RSC)
Date: 2008
DOI: 10.1039/B809868A
Abstract: The reaction profile for sulfide oxidation by formally Mn(V)=O species depends critically on the electronic structure of the isolated oxidant. In cases where the ground state has dominant oxyl radical character, the oxidation occurs in sequential one-electron steps, the first of which is barrierless. In contrast, if the oxyl radical character is 'masked' in the ground state by electron transfer from either the metal or the porphyrin co-ligand, the interaction between oxidant and substrate is repulsive at large separations, only becoming attractive when the incoming nucleophile approaches close enough to drive an electron out of oxide ppi manifold, thereby 'unmasking' the oxyl radical. The shape of the repulsive wall at long range will depend on the properties of both oxidant and substrate, offering the potential for substrate discrimination that is one of the most remarkable properties of the oxygen evolving complex. The electronic properties of the oxidant depend critically on the identity of the axial co-ligand, but also on the chosen density functional. As a result, hybrid and non-hybrid functionals give very different qualitative descriptions of the oxidation reaction.
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/D0DT01325K
Abstract: Herein, we found that nitrogen donor dpp − ligand is flexible and provides a platform for aggregation of Ru 2+ and/or Ru 3+ to give a new type of face-sharing bi-octahedra Ru 2 5+ and Ru 2 6+ dimer featuring of distinct metal–metal bond bond between two ruthenium centres.
Publisher: MDPI AG
Date: 30-05-2022
DOI: 10.3390/INORGANICS10060075
Abstract: In this paper, we report the synthesis and structural characterisation of two hetero-metallic clusters, [(CO)3CrSn5Cr(CO)3]4− and [(CO)3MoSn5Mo(CO)3]4−, both of which have a pentagonal bipyramidal core. The structures are similar to that of previously reported [(CO)3MoPb5Mo(CO)3]4− and our analysis of the bonding suggests that they are best formulated as containing Sn54− rings bridging two zerovalent M(CO)3 fragments. The electronic structure is compared to two isolobal M2E5 clusters, [CpCrP5CrCp]− and Tl77−, both of which show clear evidence for trans-annular bonds between the apical atoms that is not immediately obvious in the title clusters. Our analysis shows that the balance between E-E and M-M bonding is a delicate one, and shifts in the relative energies of the orbitals on the E5 and M2 fragments generate a continuum of bonding situations linked by the degree of localisation of the cluster LUMO.
Publisher: Wiley
Date: 04-11-2016
Publisher: Wiley
Date: 17-08-2007
Abstract: Abstraction of a Cl(-) ion from the P-chlorophospholes, R4C4PCl (R=Me, Et), produced the P--P bonded cations [R4C4P--P(Cl)C4R4]+, which reacted with PPh3 to afford X-ray crystallographically characterised phosphine-phosphenium cations [R4C4P(PPh3)]+ (R=Me, Et). Examination of the 31P-{1H} NMR spectrum of a solution (CH2Cl(2)) of [Et4C4P-(PPh3)]+ and PPh3 revealed broadening of the resonances due to both free and coordinated PPh3, and importantly it proved possible to measure the rate of exchange between PPh3 and [Et4C4P-(PPh3)]+ by line shape analysis (gNMR programmes). The results established second-order kinetics with DeltaS( not equal)=(-106.3+/-6.7) J mol(-1) K(-1), DeltaH( not equal)=(14.9+/-1.6) kJ mol(-1) and DeltaG( not equal) (298.15 K)=(46.6+/-2.6) kJ mol(-1), values consistent with a SN2-type pathway for the exchange process. This result contrasts with the dominant dissociative (S(N)1-type) pathway reported for the analogous exchange reactions of the [ArNCH2CH2N(Ar)P(PMe3)]+ ion, and to understand in more detail the factors controlling these two different reaction pathways, we have analysed the potential energy surfaces using density functional theory (DFT). The calculations reveal that, whilst phosphine exchange in [Et4C4P(PPh3)]+ and [ArNCH2CH2N(Ar)P(PMe3)](+) is superficially similar, the two cations differ significantly in both their electronic and steric requirements. The high electrophilicity of the phosphorus center in [Et4C4P]+, combined with strong pi-pi interactions between the ring and the incoming and outgoing phenyl groups of PPh3, favours the SN2-type over the SN1-type pathway in [Et4C4P(PPh3)]+. Effective pi-donation from the amide groups reduces the intrinsic electrophilicity of [ArNCH2CH2N(Ar)P]+, which, when combined with the steric bulk of the aryl groups, shifts the mechanism in favour of a dissociative SN1-type pathway.
Publisher: Elsevier
Date: 2013
Publisher: Wiley
Date: 21-02-2011
Publisher: SAGE Publications
Date: 13-01-2075
Abstract: Antipsychotic drug treatment alters status on key risk factors for cardiovascular disease. The aim of this study was to test whether cardiovascular risk factor associations differ in adults with psychosis and adults from the general community. Data were analysed for those aged 25–64 years from a nationally representative psychosis s le ( n = 1,457) and a national comparator s le ( n = 8,866). The Pearson correlation coefficient was used to estimate the association among tobacco use, body mass index, waist circumference, diastolic and systolic blood pressure and fasting total-, LDL- and HDL-cholesterol, triglycerides and plasma glucose. The robust Levene test was used to test for s le differences in variance. Correlations among cardiovascular risk indicators and between cardiovascular risk indicators and age were often significantly weaker in those with psychosis than in those from the national comparator s le. This was not due to a reduction in variance within the psychosis s le. Risk prediction that synthesizes multivariate risk indicator data needs to be connected to verified cardiovascular morbidity and mortality in those with psychosis to determine if standard risk calculators adequately discriminate those at high, medium and low future risk of cardiovascular morbidity and mortality. Until then the clinical implications of low or absent correlations among cardiovascular risk indicators and their low or absent association with increasing age is unclear but may indicate that risk equations commonly used in the general population may not be applicable for those with treated psychosis.
Publisher: American Chemical Society (ACS)
Date: 18-10-2022
Publisher: Royal Society of Chemistry (RSC)
Date: 2001
DOI: 10.1039/B006368L
Publisher: American Chemical Society (ACS)
Date: 12-11-2012
DOI: 10.1021/OM300928J
Publisher: American Chemical Society (ACS)
Date: 28-12-2010
DOI: 10.1021/IC101691Q
Abstract: Six [Fe(8)(μ(4)-O)(4)(μ-4-R-pyrazolato)(12)X(4)] complexes containing an identical Fe(8)(μ(4)-O)(4) core have been structurally characterized and studied by Mössbauer spectroscopy. In each case, an inner μ(4)-O bridged Fe(III) cubane core is surrounded by four trigonal bipyramidal iron centers, the two distinct sites occurring in a 1:1 ratio. The Mössbauer spectrum of each of the clusters consists of two quadrupole doublets, which, with one exception (X = NCS, R = H), overlap to give three absorption lines. The systematic variation of X and R causes significant changes in the Mössbauer spectra. A comparison with values for the same clusters computed using density functional theory allows us to establish an unequivocal assignment of these peaks in terms of a nested model for the overlapping doublets. The changes in Mössbauer parameters (both experimental and computed) for the 1-electron reduced species [Fe(8)(μ(4)-O)(4)(μ-4-Cl-pyrazolato)(12)Cl(4)](-) are consistent with a redox event that is localized within the cubane core.
Publisher: American Chemical Society (ACS)
Date: 12-08-2016
DOI: 10.1021/ACS.INORGCHEM.6B01484
Abstract: Topochemical reduction of the ordered double perovskite LaSrNiRuO6 with CaH2 yields LaSrNiRuO4, an extended oxide phase containing infinite sheets of apex-linked, square-planar Ni(1+)O4 and Ru(2+)O4 units ordered in a checkerboard arrangement. At room temperature the localized Ni(1+) (d(9), S = (1)/2) and Ru(2+) (d(6), S = 1) centers behave paramagnetically. However, on cooling below 250 K the system undergoes a cooperative phase transition in which the nickel spins align ferromagnetically, while the ruthenium cations appear to undergo a change in spin configuration to a diamagnetic spin state. Features of the low-temperature crystal structure suggest a symmetry lowering Jahn-Teller distortion could be responsible for the observed diamagnetism of the ruthenium centers.
Publisher: American Chemical Society (ACS)
Date: 09-06-2010
DOI: 10.1021/IC100817S
Abstract: Addition of potassium metal and 2,2,2-crypt (4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane) to a tetrahydrofuran (THF) solution of Fe(2,2'-bipyridine)(mes)(2) (1 mes = 2,4,6-Me(3)C(6)H(2)) yielded the anionic complex [Fe(2,2'-bipyridine)(mes)(2)](-) which was isolated as [K(2,2,2-crypt)][Fe(2,2'-bipyridine)(mes)(2)] (2) alongside the side-product [K(2,2,2-crypt)][Fe(mes)(3)] x C(6)H(12) (3). A compositionally pure s le of 2 was obtained by dissolving a mixture of 2 and 3 in dry pyridine and layering the resulting solution with toluene. Solid state magnetic susceptibility measurements on 1 reveal Curie-Weiss paramagnetic behavior with a molar magnetic moment of 5.12(1) mu(B) between 20 and 300 K, a value which is in line with the expected iron(II) spin-only value of 4.90 mu(B). The magnetic measurements carried out on 2 reveal more complex temperature dependent behavior consistent with intramolecular antiferromagnetic coupling (J = -46 cm(-1)) between the unpaired electrons of the iron(II) ion (S(Fe) = 2) and a pi* orbital of the bipyridyl radical (S(bipy) = 1/2). Structural data, Mossbauer and electron paramagnetic resonance (EPR) spectroscopic measurements, and density functional theory (DFT) calculations are all consistent with this model of the electronic structure. To the best of our knowledge, species 2 represents the first crystallographically characterized transition metal complex of the 2,2'-bipyridyl ligand for which magnetic, spectroscopic, and computational data indicate the presence of an unpaired electron in the pi* antibonding orbital.
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D1CS00775K
Abstract: Despite many different views on the bonding in endohedral Zintl clusters, the relationship between their valence electron count and their structure and bonding patterns is much more uniform than previously anticipated, as highlighted in this article.
Publisher: American Chemical Society (ACS)
Date: 14-12-2007
DOI: 10.1021/IC7020337
Publisher: American Chemical Society (ACS)
Date: 09-11-2022
DOI: 10.1021/JACS.2C08559
Publisher: Royal Society of Chemistry (RSC)
Date: 2009
DOI: 10.1039/B908109G
Abstract: Treatment of [AuCl(PBu(t)(3))] with AgSbF(6) in CH(2)Cl(2) at room temperature in the presence of the alkenes norbornene, norbornadiene, trans-cyclooctene, and also interestingly, isobutylene, leads to the formation of stable crystalline complexes [Au(PBu(t)(3))(alkene)][SbF(6)], characterised by NMR spectroscopy and X-ray crystallography.
Publisher: American Chemical Society (ACS)
Date: 30-07-2017
DOI: 10.1021/IC301587F
Abstract: The organometallic first-row transition-metal complexes [M(2,2'-bipy)(mes)2] (M = Cr (1), Mn (2), Co (4), Ni (5) 2,2'-bipy = 2,2'-bipyridine mes = 2,4,6-Me3C6H2) were reacted with potassium and a suitable alkali-metal sequestering agent to yield salts of the anionic species [M(2,2'-bipy)(mes)2](-). The neutral parent compounds and their corresponding anionic congeners were characterized by single-crystal X-ray diffraction in [Cr(2,2'-bipy)(mes)2]·1.5C6H6, [Mn(2,2'-bipy)(mes)2], [Co(2,2'-bipy)(mes)2]·THF, [Ni(2,2'-bipy)(mes)2], [K(dibenzo-18-crown-6)·THF][Cr(2,2'-bipy)(mes)2]·2THF, [K(18-crown-6)][Mn(2,2'-bipy)(mes)2]·2THF, [K(18-crown-6)][Mn(2,2'-bipy)(mes)2]·0.67py·0.67tol, [K(2,2,2-crypt)][Co(2,2'-bipy)(mes)2], and [K(2,2,2-crypt)][Ni(2,2'-bipy)(mes)2]. These species, along with the previously reported neutral and anionic iron complexes [Fe(2,2'-bipy)(mes)2](0/-) (3/3(-)), form a homologous series of compounds which allow for an in-depth study of the interactions between metals and ligands. Single-crystal X-ray diffraction data, DFT calculations, and various spectroscopic and magnetic measurements indicate that the anionic complexes (1(-)-5(-)) can be best formulated as M(II) complexes of the 2,2'-bipyridyl radical anion. These findings complement recent studies which indicate that bond metric data from single-crystal X-ray diffraction may be employed as an important diagnostic tool in determining the oxidation states of bipyridyl ligands in transition-metal complexes.
Publisher: American Chemical Society (ACS)
Date: 20-09-2011
DOI: 10.1021/IC200708C
Abstract: The reaction of 3 equiv of the ligand 2-[(2-chlorophenyl)azo]pyridine (L(a)) or 2-[(4-chlorophenyl)azo]pyridine (L(b)) with 1 equiv of Cr(CO)(6) or Mo(CO)(6) in boiling n-octane afforded [Cr(L(a/b))(3)](0) (1a and 1b) and [Mo(L(a/b))(3)](0) (2a and 2b). The chemical oxidation reaction of these neutral complexes with I(2) in CH(2)Cl(2) provided access to air-stable one-electron-oxidized species as their triiodide (I(3)(-)) salts. The electronic structures of chromium and molybdenum centers coordinated by the three redox noninnocent ligands L(a/b) along with their redox partners have been elucidated by using a host of physical methods: X-ray crystallography, magnetic susceptibility measurements, nuclear magnetic resonance, cyclic voltammetry, absorption spectroscopy, electron paramagnetic resonance spectroscopy, and density functional theory. The four representative complexes, 1a, [1a]I(3), 2a, and [2a]I(3), have been characterized by X-ray crystallography. The results indicate a predominant azo-anion-radical description of the ligands in the neutral chromium(III) species, [Cr(III)(L(•-))(3)], affording a singlet ground state through strong metal-ligand antiferromagnetic coupling. All of the electrochemical processes are ligand-based i.e., the half-filled (t(2g))(3) set of the Cr(III) d(3) ion remains unchanged throughout. The description of the molybdenum analogue is less clear-cut because mixing between metal- and ligand-based orbitals is more significant. On the basis of variations in net spin densities and orbital compositions, we argue that the oxidation events are again primarily ligand-based, although the electron density at the molybdenum center is clearly more variable than that at the chromium center in the corresponding series [1a](+), 1a, and [1a](-).
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7DT02257C
Abstract: The structural chemistry of the M@Si 14 family of clusters is controlled by the availability of d-electron density on the encapsulated metal.
Publisher: American Chemical Society (ACS)
Date: 09-10-2018
DOI: 10.1021/ACS.INORGCHEM.8B02198
Abstract: Topochemical reduction of the double-perovskite oxide Sr
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C4DT03573A
Abstract: Like the pieces of a jigsaw, maximum stability in clusters is achieved when electron density on metal and cage interlock.
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C9CP01841G
Abstract: The absorption of endohedral clusters on Si(111)-7 × 7 generates a new bond between W and a surface silicon adatom.
Publisher: Wiley
Date: 23-03-2018
Abstract: The synthesis of the first 4d transition metal oxide-hydride, LaSr
Publisher: Springer Science and Business Media LLC
Date: 10-07-2020
DOI: 10.1038/S41467-020-17187-4
Abstract: Gold nanoparticles have been used for centuries, both for decoration and in medical applications. More recently, many of the major advances in cluster chemistry have involved well-defined clusters containing tens or hundreds of atoms, either with or without a ligand shell. In this paper we report the synthesis of two gold/lead clusters, [Au 8 Pb 33 ] 6− and [Au 12 Pb 44 ] 8− , both of which contain nido [Au@Pb 11 ] 3− icosahedra surrounding a core of Au atoms. Analogues of these large clusters are not found in the corresponding Ag chemistry: instead, the Ag-centered nido icosahedron, [Ag@Pb 11 ] 3− , is the only isolated product. The structural chemistry, along with the mass spectrometry which shows the existence of [Au 2 Pb 11 ] 2− but not [Ag 2 Pb 11 ] 2− , leads us to propose that the former species is the key intermediate in the growth of the larger clusters. Density functional theory indicates that secondary π-type interactions between the [Au@Pb 11 ] 3− ligands and the gold core play a significant part in stabilizing the larger clusters.
Publisher: American Chemical Society (ACS)
Date: 20-05-2021
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/C9SC05969E
Abstract: We report on the ( tert -butyl)isocyanide-catalysed isomersation of a phosphaethynolato-borane, [B]OCP, to its linkage isomer, a phosphaketenyl-borane, [B]PCO.
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C2SC01024K
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C8SC03948H
Abstract: Triply fused cluster: edge shared of three [Rh@Sn 10 ] subunits lead to the largest endohedral polystannide with an entirely new triply fused topology.
Publisher: Royal Society of Chemistry (RSC)
Date: 2008
DOI: 10.1039/B715021K
Abstract: Density functional theory is used to explore the electronic states involved in the remarkable two-step spin crossover (S = 0 --> S = 1 --> S = 2) in the cationic extended metal atom chain [Co(3)(dpa)(4)Cl(2)](+) (dpa = the anion of 2-dipyridylamine) (R. Clérac, F. A. Cotton, K. R. Dunbar, T. Lu, C. A. Murillo and X. Wang, J. Am. Chem. Soc., 2000, 122, 2272). The calculations are consistent with a model in which all three spin states share one common feature-a vacancy in the d(xy) orbital on the central cobalt atom which is stabilised by pi donation from four amide groups. As a result, all three can be considered to contain a Co(2+)-Co(3+)-Co(2+) chain. The singlet and triplet states arise from antiferromagnetic and ferromagnetic coupling, respectively, between the unpaired electron in this d(xy) orbital and another localised entirely on the terminal cobalt centres (the antisymmetric combination of Co d(z(2))). The singlet-triplet transition does not, therefore, populate any additional antibonding orbitals, and as a result the structure is almost invariant around the characteristic temperature of the singlet-triplet transition. In the most stable quintet, in contrast, the symmetry of the Co-Co-Co chain is broken, giving rise to a localised high-spin Co(II) centre (S = 3/2), ferromagnetically coupled to a Co(III)-Co(II) dimer (S = 1/2). The structural changes associated with this transition are apparent in the X-ray data in subtle changes in both Co-N and Co-Cl bond lengths, although their magnitude is d ed by the relatively low population (18%) of the quintet even at 300 K.
Publisher: American Chemical Society (ACS)
Date: 22-04-2022
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3DT50617G
Abstract: The O2 binding affinity of a series of dicobalt(II) complexes can be tuned between p(O2)50% = 2.3 × 10(-3) and 700 × 10(-3) atm at 40 °C by varying the number of H and Cl atoms in the bridging acetato ligands of [Co2(bpbp)(CH(3-n)ClnCO2)(CH3CN)2](2+), where bpbp(-) = 2,6-bis(N,N-bis(2-pyridylmethyl)aminomethyl)-4-tert-butylphenolate and n = {0, 1, 2, 3}. O2 binds most strongly to the deoxy complex containing the acetato bridge and the O2 affinity decreases linearly as the number of Cl atoms is increased from 0 to 3 in [Co2(bpbp)(O2)(CH3CO2)](2+), [Co2(bpbp)(O2)(CH2ClCO2)](2+), [Co2(bpbp)(O2)(CHCl2CO2)](2+) and [Co2(bpbp)(O2)(CCl3CO2)](2+). The O2 affinities can be qualitatively correlated with both the pKa value of the parent acetic or chloroacetic acid and the redox potential of the O2(2-)/O2˙(-) couple measured for the peroxide-bridged complexes. The redox potential varies between 510 mV (vs. Fc(0/+)) for the acetato-bridged complex to 696 mV for the trichloroacetato-bridged system. Despite the clear difference in reactivity in solution, there are no clear trends which can be correlated to O2 affinity in the O-O bond lengths in the X-ray crystal structures at 180 K (1.415(4)-1.424(2) Å) or in the frequencies of the peroxido O-O stretch in the solid-state resonance Raman spectra at 298 K (830-836 cm(-1)). Using density functional theory calculations, we conclude that the Co(II) atoms of the deoxy complexes coordinate solvent molecules as auxiliary ligands and that a conformation change of the ligand is involved in the reversible O2 binding process. The alternative of five coordination in the deoxy Co(II) complexes is therefore seen as less likely. The crystal structure and p(O2)50% are also reported for the 1-naphthoato-bridged oxy complex [Co2(bpbp)(O2)(C10H7O2)](2+), and the O2 binding affinity in that case is also qualitatively consistent with the expectation from the pKa of the parent 1-naphthoic acid.
Publisher: American Chemical Society (ACS)
Date: 08-03-2021
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C2CC35746A
Abstract: The Fe(IV)oxo complex of a coordinatively flexible multidentate mono-carboxylato ligand is obtained by the one electron oxidation of a low spin Fe(III) precursor in water.
Publisher: Royal Society of Chemistry (RSC)
Date: 2006
DOI: 10.1039/B517710C
Abstract: The cationic cages nido-[C2Bu(t)2P2E]+ (E = As, Sb), which are isolobal to the cyclopentadienyl cation, adopt square based pyramidal structures with the heavy pnictogen atom at the apex NMR and computational methods have been used to probe the dynamic behaviour of the complexes.
Publisher: Wiley
Date: 16-11-2009
Publisher: Royal Society of Chemistry (RSC)
Date: 2009
DOI: 10.1039/B822225H
Abstract: The synthesis and X-ray crystal structures of the diborane(4) isomers 1,1-B(2){1,2-(NH)(2)C(6)H(4)}(2) and 1,2-B(2){1,2-(NH)(2)C(6)H(4)}(2) are described together with the results of quantum chemical calculations which shed light on their relative stabilities and degree of aromaticity. Spectroscopic data are also provided for both isomers of the 4-methyl aryl derivative. The compound 1,1-B(2){1-O-2-(NH)C(6)H(4)}(2) has also been prepared and structurally characterised but no evidence was obtained for the corresponding 1,2-isomer. The compound 1,1-B(2){1,2-(NH)(2)C(6)H(4)}(2) forms a co-crystal with TCNQ, the structure of which is also reported.
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C2CC36888A
Abstract: Reaction of an ethylenediamine solution of K(3)As(7) with the low-valent, low-coordinate cobalt(II) complex [Co(mes)(2)(PEt(2)Ph)(2)] yielded the novel dianionic species [Co(η(3)-As(3)){η(4)-As(4)(mes)(2)}](2-) (1). The [η(4)-As(4)(mes)(2)](2-) moiety present in 1 is a rare ex le of a group 15 analogue of a butadienediide.
Publisher: American Chemical Society (ACS)
Date: 21-01-2009
DOI: 10.1021/OM800999A
Publisher: American Chemical Society (ACS)
Date: 21-08-2012
DOI: 10.1021/JP304807W
Publisher: American Chemical Society (ACS)
Date: 20-03-2002
DOI: 10.1021/JA017303T
Abstract: This paper describes the efficient synthesis and full characterization of rare formally zerovalent and diamagnetic monovalent pseudooctahedral niobium and tantalum complexes. The reaction of NbCl(4)(thf)(2) with 4 equiv of Na and 3.5 equiv of iPr(2)-dad (1,4-diisopropyl-1,4-diaza-1,3-diene) yields Nb(iPr(2)-dad)(3) in 52% yield. Ta(iPr(2)-dad)(3) is also obtained in 33% yield from 5 equiv of Na/naphthalene and 3.5 equiv of iPr(2)-dad. Oxidation of these complexes with AgBPh(4) yields the diamagnetic complexes [M(iPr(2)-dad)(3)][BPh(4)] (M = Nb, Ta). X-ray and spectroscopic data indicate that the unpaired electron density is localized on the ligands. DFT calculations reveal that, in the prevailing D(3) symmetry, a very strong splitting of t(2g) metal-based orbitals occurs, leading to the diamagnetism of the 16e M(iPr(2)-dad)(3)(+). This strong splitting allows a M-N nonbonding, ligand-based orbital to accommodate additional electrons, as a result of which the formally zerovalent complexes, M(iPr(2)-dad)(3), are in fact correctly formulated as M(+)iPr(2)-dad (-), that is, (16e + 1e).
Publisher: Springer International Publishing
Date: 2016
DOI: 10.1007/430_2015_209
Publisher: Wiley
Date: 17-12-2004
Abstract: Density functional theory has been used to assess the role of the bimetallic core in supporting reductive cleavage of the N=N double bond in [Cp2Mo2(mu-SMe)3(mu-eta1:eta1-HN=NPh)]+. The HOMO of the complex, the Mo-Mo delta orbital, plays a key role as a source of high-energy electrons, available for transfer into the vacant orbitals of the N=N unit. As a result, the metal centres cycle between the Mo(III) and Mo(IV) oxidation states. The symmetry of the Mo-Mo delta "buffer" orbital has a profound influence on the reaction pathway, because significant overlap with the redox-active orbital on the N=N unit (pi* or sigma*) is required for efficient electron transfer. The orthogonality of the Mo-Mo delta and N-N sigma* orbitals in the eta1:eta1 coordination mode ensures that electron transfer into the N-N sigma bond is effectively blocked, and a rate-limiting eta1:eta1-->eta1 rearrangement is a necessary precursor to cleavage of the bond.
Publisher: American Chemical Society (ACS)
Date: 26-05-2007
DOI: 10.1021/CT700043W
Abstract: In previous studies of the agostic bonding in Tp(Me2)NbCl(R'CCR' ')(R), we have made use of a hybrid QM/MM protocol (B3LYP:UFF) where the QM partition ([Nb(Cl)(iPr)(HCCH)(NHCH2)3](+)) was rather small, but the optimized structures were nevertheless in apparently good agreement with experiment. In attempting to improve this model by expanding the size of the QM region, we were surprised to discover that a full QM treatment of the whole molecule using the B3LYP functional failed to locate an agostic structure of any kind. A systematic assessment of density functionals reveals that the poor performance of B3LYP in these systems is typical of all DFT methods that do not obey the uniform electron gas (UEG) correlation limit. Those that do obey the UEG limit, in contrast, provide an excellent description of the agostic structure when the complete ligand system is treated at the QM level. The apparently good performance of our original (B3LYP:UFF) hybrid method can be traced to a cancellation of errors: the B3LYP functional underestimates the intrinsic strength of the agostic interaction relative to competing Nb-Cl π bonding, but this is offset by an additional but unphysical electrostatic component to the agostic bond introduced by the presence of a positive charge in the QM region.
Publisher: MDPI AG
Date: 12-04-2019
DOI: 10.3390/INORGANICS7040052
Abstract: Density Functional Theory and Complete Active Space Self-Consistent Field (CASSCF) methodologies are used to explore the electronic structure of the cationic V–N clusters, [V4N4]+ and [V6N6]+, that have been identified in recent mass spectrometric experiments. Our calculations indicate that both clusters are based on cubane-like fragments of the rock-salt lattice. In the smaller [V4N4]+ cluster, the V–V bonding is delocalized over the tetrahedron, with net bond orders of 1/3 per V–V bond. In [V6N6]+, in contrast, the V–V bonding is strongly localized in the central V2N2 unit, which has a short V=V double bond. CASSCF calculations reveal that both localized and delocalized V–V bonds are highly multi-configurational.
Publisher: Royal Society of Chemistry (RSC)
Date: 2006
DOI: 10.1039/B516393E
Abstract: The synthesis and characterisation of the cyclobutyl complex Tp(Me2)NbCl(c-C4H7)(MeC[triple bond]CMe) completes the family of cycloalkyl complexes Tp(Me2)NbCl(c-C(n)H(2n-1)), n = 3-6. The properties of the cyclobutyl complex are qualitatively similar to those of its cyclopentyl and cyclohexyl analogues, and dramatically different from those of the cyclopropyl derivative. Most conspicuously, the cyclobutyl system has an alpha-C-H agostic interaction in the dominant isomer, with no evidence for the alpha-C-C agostic character found for the smaller ring. C-C agostic character therefore seems to be unique to the cyclopropyl complex, where the acute C-C-C angles destabilise the C-C bonding orbitals.
Publisher: American Chemical Society (ACS)
Date: 21-09-2010
DOI: 10.1021/JA1061505
Abstract: We report the synthesis of a niobium cyclopropyl complex, Tp(Me2)NbMe(c-C(3)H(5))(MeCCMe), and show that thermal loss of methane from this compound generates an intermediate that is capable of activating both aliphatic and aromatic C-H bonds. Isotopic labeling, trapping studies, a detailed kinetic analysis, and density functional theory all suggest that the active intermediate is an η(2)-cyclopropene complex formed via β-hydrogen abstraction rather than an isomeric cyclopropylidene species. C-H activation chemistry of this type represents a rather unusual reactivity pattern for η(2)-alkene complexes but is favored in this case by the strain in the C(3) ring which prevents the decomposition of the key intermediate via loss of cyclopropene.
Publisher: American Chemical Society (ACS)
Date: 06-07-2011
DOI: 10.1021/OM200199E
Publisher: Wiley
Date: 21-12-2007
Publisher: Royal Society of Chemistry (RSC)
Date: 2006
DOI: 10.1039/B512298H
Abstract: Density functional theory reveals the detailed mechanism of alcohol oxidation by a model copper complex, Cu(II)L, L = cis-1-(3',5'-dimethoxy-benzylideneamino)-3,5-[2-hydroxy-(3',5'-di-tert-butyl)benzylideneimino]cyclohexane. Despite the obvious structural and functional parallels between the title compound and the enzyme galactose oxidase, the details of the catalytic pathway are fundamentally different. In the enzyme, coordination of the substrate produces an active form containing a Cu(II) centre and a tyrosyl radical, the latter being responsible for the abstraction of hydrogen from the substrate. In the model system, in marked contrast, the active form contains a Cu(II) centre, but the ligand radical character is localised on the substrate (alcoholate) oxygen, rather than the phenolate ligand. The result is a significantly higher barrier to hydrogen-atom abstraction compared to the enzyme itself. The origin of these significant differences is traced to the rigid nature of the pentadentate ligand, which resists changes in coordination number during the catalytic cycle.
Publisher: Royal Society of Chemistry (RSC)
Date: 2011
DOI: 10.1039/C1DT10594A
Abstract: The monoanionic N(4)O ligand N-methyl-N,N'-bis(2-pyridylmethyl)ethylenediamine-N'-acetate (mebpena(-)) undergoes oxidative C-N bond cleavage in the presence of Co(II) and O(2). The two resultant fragments are coordinated to the metal ion in the product [Co(III)(2-pyridylformate)(mepena)]ClO(4) (mepena(-) = N-methyl-N'-(2-pyridylmethyl)ethylenediamine-N'-acetato). Bond cleavage does not occur in the presence of chloride ions and [Co(III)(mebpena)Cl](+), containing intact mebpena(-), can be isolated. The oxidative instability of the mebpena(-) in the presence of Co(II) and air stands in contrast to the oxidative stability of the family of very closely related penta- and hexa-dentate ligands in their cobalt complexes. Cyclic voltammetry on the matched pair [Co(III)Cl(mebpena)](+) and [Co(II)Cl(bztpen)](+), bztpen = N-benzyl-N,N',N'-tris(2-pyridylmethyl)ethylenediamine, shows that substitution of a pyridine donor for a carboxylato donor results in a relatively small cathodic shift of 150 mV in the E°(Co(II)/Co(III)) oxidation potential, presumably this is enough to determine the contrasting metal oxidation state in the complexes isolated under ambient conditions. DFT calculations support a proposal that [Co(II)(mebpena)](+) reacts with O(2) to form a Co(III)-superoxide complex which can abstract an H atom from a ligand methylene C atom as the initial step towards the observed oxidative C-N bond cleavage.
Publisher: Royal Society of Chemistry (RSC)
Date: 2003
DOI: 10.1039/B305296F
Publisher: American Chemical Society (ACS)
Date: 15-11-2006
DOI: 10.1021/OM060712J
Publisher: American Chemical Society (ACS)
Date: 16-03-2011
DOI: 10.1021/AR100136X
Abstract: In this Account, we describe the transition metal-mediated cleavage of C-F and C-H bonds in fluoroaromatic and fluoroheteroaromatic molecules. The simplest reactions of perfluoroarenes result in C-F oxida tive addition, but C-H activation competes with C-F activation for partially fluorinated molecules. We first consider the reactivity of the fluoroaromatics toward nickel and platinum complexes, but extend to rhenium and rhodium where they give special insight. Sections on spectroscopy and molecular structure are followed by discussions of energetics and mechanism that incorporate experimental and computational results. We highlight special characteristics of the metal-fluorine bond and the influence of the fluorine substituents on energetics and mechanism. Fluoroaromatics reacting at an ML(2) center initially yield η(2)-arene complexes, followed usually by oxidative addition to generate MF(Ar(F))(L)(2) or MH(Ar(F))(L)(2) (M is Ni, Pd, or Pt L is trialkylphosphine). The outcome of competition between C-F and C-H bond activation is strongly metal dependent and regioselective. When C-H bonds of fluoroaromatics are activated, there is a preference for the remaining C-F bonds to lie ortho to the metal. An unusual feature of metal-fluorine bonds is their response to replacement of nickel by platinum. The Pt-F bonds are weaker than their nickel counterparts the opposite is true for M-H bonds. Metal-fluorine bonds are sufficiently polar to form M-F···H-X hydrogen bonds and M-F···I-C(6)F(5) halogen bonds. In the competition between C-F and C-H activation, the thermodynamic product is always the metal fluoride, but marked differences emerge between metals in the energetics of C-H activation. In metal-fluoroaryl bonds, ortho-fluorine substituents generally control regioselectivity and make C-H activation more energetically favorable. The role of fluorine substituents in directing C-H activation is traced to their effect on bond energies. Correlations between M-C and H-C bond energies demonstrate that M-C bond energies increase far more on ortho-fluorine substitution than do H-C bonds. Conventional oxidative addition reactions involve a three-center triangular transition state between the carbon, metal, and X, where X is hydrogen or fluorine, but M(d)-F(2p) repulsion raises the activation energies when X is fluorine. Platinum complexes exhibit an alternative set of reactions involving rearrangement of the phosphine and the fluoroaromatics to a metal(alkyl)(fluorophosphine), M(R)(Ar(F))(PR(3))(PR(2)F). In these phosphine-assisted C-F activation reactions, the phosphine is no spectator but rather is intimately involved as a fluorine acceptor. Addition of the C-F bond across the M-PR(3) bond leads to a metallophosphorane four-center transition state subsequent transfer of the R group to the metal generates the fluorophosphine product. We find evidence that a phosphine-assisted pathway may even be significant in some apparently simple oxidative addition reactions. While transition metal catalysis has revolutionized hydrocarbon chemistry, its impact on fluorocarbon chemistry has been more limited. Recent developments have changed the outlook as catalytic reactions involving C-F or C-H bond activation of fluorocarbons have emerged. The principles established here have several implications for catalysis, including the regioselectivity of C-H activation and the unfavorable energetics of C-F reductive elimination. Palladium-catalyzed C-H arylation is analyzed to illustrate how ortho-fluorine substituents influence thermodynamics, kinetics, and regioselectivity.
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C8DT03833C
Abstract: A series of tricobalt EMACs with halide axial ligands demonstrate erse spin-crossover behaviors as a function of the molecular geometry and the nature of the axial ligand.
Publisher: Royal Society of Chemistry (RSC)
Date: 2011
DOI: 10.1039/C0DT01362E
Abstract: Density functional theory is used to explore possible mechanisms that lead to water oxidation by a bimetallic manganese catalyst developed by McKenzie and co-workers. On the basis of our calculations we propose that the key active intermediate is a mixed valent Mn(III)(μ-O)Mn(IV)-O˙ oxyl radical species, the oxyl centre being the site of nucleophilic attack by water. The mixed-valent species is in equilibrium with an isomeric diamond-core Mn(IV)(μ-O)(2)Mn(IV) structure, which acts as reservoir for the active species. The chemistry appears to be unique to pentadentate ligands because these shift the position of the equilibrium between the Mn(III)(μ-O)Mn(IV)-O˙ and Mn(IV)(μ-O)(2)Mn(IV) isomers, such that significant concentrations of the former are present in solution.
Publisher: Elsevier BV
Date: 03-2009
Publisher: Elsevier BV
Date: 11-2010
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C6CP03534E
Abstract: DFT and CASPT2 calculations reveal that the ground state of [Mn@Si 12 ] + is a biradical, quite unlike isoelectronic and isostructural Cr@Si 12 .
Publisher: Royal Society of Chemistry (RSC)
Date: 2008
DOI: 10.1039/B717204D
Abstract: The electronic structure of the 1,2,3-triphosphaindenyl ligand suggests that it should exhibit enhanced pi-acceptor properties when compared to the eta(5)-indenyl system this insight encouraged us to develop a simple synthetic pathway from 1,2-diphosphinobenzene to the 1,2,3-C(6)H(4)P(3) and 2-As-1,3-C(6)H(4)P(2) anions, both of which have been structurally characterised by X-ray crystallography as a bonus from these studies we also obtained the first structurally characterised organo derivative of the P(8) unit present in Hittorf's phosphorus.
Publisher: Informa UK Limited
Date: 03-07-2023
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D1CC05043E
Abstract: A trinuclear iron cluster possesses ferromagnetically coupled high-spin Fe II centers and displays slow relaxation of the magnetization under applied field.
Publisher: American Chemical Society (ACS)
Date: 17-05-2011
DOI: 10.1021/JA203051D
Abstract: Aminoboranes, H(2)BNRR', represent the monomeric building blocks from which novel polymeric materials can be constructed via metal-mediated processes. The fundamental capabilities of these compounds to interact with metal centers have been probed through the coordination of H(2)BNCy(2) at 16-electron [CpRu(PR(3))(2)](+) fragments. In contrast to the side-on binding of isoelectronic alkene donors, an alternative mono(σ-BH) mode of aminoborane ligation is established for H(2)BNCy(2), with binding energies only ~8 kcal mol(-1) greater than those for analogous dinitrogen complexes. Variations in ground-state structure and exchange dynamics as a function of the phosphine ancillary ligand set are consistent with chemically significant back-bonding into an orbital of B-H σ* character.
Publisher: American Chemical Society (ACS)
Date: 28-01-2013
DOI: 10.1021/JA309798E
Abstract: Low-temperature topochemical reduction of the cation disordered perovskite phase SrFe(0.5)Ru(0.5)O(3) with CaH(2) yields the infinite layer phase SrFe(0.5)Ru(0.5)O(2). Thermogravimetric and X-ray absorption data confirm the transition metal oxidation states as SrFe(0.5)(2+)Ru(0.5)(2+)O(2) thus, the title phase is the first reported observation of Ru(2+) centers in an extended oxide phase. DFT calculations reveal that, while the square-planar Fe(2+) centers adopt a high-spin S = 2 electronic configuration, the square-planar Ru(2+) cations have an intermediate S = 1 configuration. This combination of S = 2, Fe(2+) and S = 1, Ru(2+) is consistent with the observed spin-glass magnetic behavior of SrFe(0.5)Ru(0.5)O(2).
Publisher: Wiley
Date: 11-08-2014
Publisher: American Chemical Society (ACS)
Date: 03-1997
DOI: 10.1021/JA9602197
Publisher: Wiley
Date: 29-07-2012
Abstract: A carbon copy: The chemical activation of the heptaphosphide trianion with [Co(PEt(2)Ph)(2)(mes)(2)] (see picture 1) yields the novel phospha-organometallic complex [Co(η(5)-P(5)){η(2)-P(2)H(mes)}](2-) (2). The reaction product maintains the nuclearity of the parent cluster, but extensive cage fragmentation takes place to yield a diamagnetic "inorganometallic" cobalt complex.
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C4DT00020J
Abstract: The influence of double exchange on the magnetic properties of a mixed-valent Fe 4 O 8 cluster is highly dependent on temperature.
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C2DT12057G
Abstract: Density functional theory has been used to provide atomic-level detail on the structures of metal hydride intermediates that have previously been proposed in the hydrogenation of phenylacetylene using Ru(3)(CO)(10)(PPh(3))(2). Based on a comparison of energetic data along with computed chemical shifts and coupling constants, we suggest that the detected species share a Ru(3)(μ-H)(μ-H) motif, with two distinct bridging hydride sites, rather than the terminal hydride proposed previously. The work illustrates how theory can be used as a complement to spectroscopy to enhance the accuracy of deductions, and to provide a basis for future rational design of second generation catalysts.
Publisher: Royal Society of Chemistry (RSC)
Date: 1992
DOI: 10.1039/C39920001272
Publisher: Wiley
Date: 03-09-2019
Abstract: The aromatic heterocycle 2,4,6-tri-tert-butyl-1,3,5-triphosphabenzene reacts with a series of silanes, germanes and stannanes, with weaker E-H bonds reacting in an increasingly facile manner. All react by 1,4-addition to give bicyclic products with diastereomeric ratios varying with the substrate. Density functional theory (DFT) calculations show that activation of the E-H bond occurs across the 1,4-C/P axis of the triphosphabenzene, with the small energetic differences with respect to the stereochemistry of the addition offering insight into the experimentally observed diastereomeric ratios.
Publisher: Elsevier BV
Date: 06-2015
Publisher: Elsevier BV
Date: 03-2008
Publisher: Royal Society of Chemistry (RSC)
Date: 2009
DOI: 10.1039/B917185A
Abstract: Reaction of an ethylenediamine solution of the intermetallic Zintl phase K4Pb9 with dimesitylcadmium yielded the dimeric Zintl ion [Pb9Cd-CdPb9]6- in low crystalline yield. The cluster anion exhibits a Cd-Cd bond and was structurally characterised by single crystal X-ray diffraction in [K(2,2,2-crypt)]6[Cd2Pb18].2en (1). DFT was also used to explore the bonding in the hexa-anionic cluster.
Publisher: American Chemical Society (ACS)
Date: 07-11-2003
DOI: 10.1021/IC034867K
Abstract: A survey of the potential energy surface for a 1:1 copper dioxygen complex, (C(3)N(2)H(5))CuO(2), reveals two distinct states in the valence region, a singlet ((1)A(1)) and a triplet ((3)B(1)). The former spans a continuum from Cu(III)-O(2)(2-) to Cu(I)-O(2)((1)Delta(g)), while the latter spans Cu(II)-O(2)(1-) to Cu(I)-O(2)((3)Sigma(g)(-)). The point at which the potential energy curves for the two states cross marks an abrupt discontinuity in electron distribution, where the system shifts from dominant Cu(III)-O(2)(2-) character to Cu(II)-O(2)(1-). On this basis, we argue that there is no continuum between Cu(III)-peroxide and Cu(II)-superoxide: the two are represented by distinct states that differ both in symmetry and multiplicity.
Publisher: American Chemical Society (ACS)
Date: 10-01-2011
DOI: 10.1021/OM101061Y
Publisher: Royal Society of Chemistry (RSC)
Date: 2007
DOI: 10.1039/B709273C
Publisher: Wiley
Date: 05-07-2011
Publisher: American Chemical Society (ACS)
Date: 21-07-2020
DOI: 10.1021/JACS.0C04815
Publisher: American Chemical Society (ACS)
Date: 04-07-2007
DOI: 10.1021/IC700429X
Abstract: The electronic structure, based on DFT calculations, of a range of FeIV=O complexes with two tetra- (L1 and L2) and two isomeric pentadentate bispidine ligands (L3 and L4) is discussed with special emphasis on the relative stability of the two possible spin states (S = 1, triplet, intermediate-spin, and S = 2, quintet, high-spin bispidines are very rigid diazaadamantane-derived 3,7-diazabicyclo[3.3.1]nonane ligands with two tertiary amine and two or three pyridine donors, leading to cis-octahedral [(X)(L)FeIV=O]2+ complexes, where X = NCCH3, OH2, OH-, and pyridine, and where X = pyridine is tethered to the bispidine backbone in L3, L4). The two main structural effects are a strong trans influence, exerted by the oxo group in both the triplet and the quintet spin states, and a Jahn-Teller-type distortion in the plane perpendicular to the oxo group in the quintet state. Due to the ligand architecture the two sites for substrate coordination in complexes with the tetradentate ligands L1 and L2 are electronically very different, and with the pentadentate ligands L3 and L4, a single isomer is enforced in each case. Because of the rigidity of the bispidine ligands and the orientation of the "Jahn-Teller axis", which is controlled by the sixth donor X, the Jahn-Teller-type distortion in the high-spin state of the two isomers is quite different. It is shown how this can be used as a design principle to tune the relative stability of the two spin states.
Publisher: Royal Society of Chemistry (RSC)
Date: 1995
DOI: 10.1039/DT9950004039
Publisher: Elsevier
Date: 2019
Publisher: Wiley
Date: 25-02-2016
Abstract: A series of cationic white phosphorus complexes of the coinage metals Au and Cu have been synthesised and characterised both in the solid state and in solution. All complexes feature a P4 unit coordinated through an edge P-P vector (η(2)-like), although the degree of activation (as measured by the coordinated P-P bond length) is greater in the gold species. All of the cations are fluxional on the NMR timescale at room temperature, but in the case of the gold systems fluxionality is frozen out at -90 °C. Electronic structure calculations suggest that this fluxionality proceeds via an η(1)-coordinated M-P4 intermediate.
Publisher: Royal Society of Chemistry (RSC)
Date: 2004
DOI: 10.1039/B405609D
Publisher: American Chemical Society (ACS)
Date: 22-04-2022
DOI: 10.1021/JACS.1C10106
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7DT01096F
Abstract: Density functional theory, Complete Active Space Self-Consistent Field (CASSCF) and perturbation theory (CASPT2) methodologies have been used to explore the electronic structure of a series of trichromium Extended Metal Atom Chains (EMACS) with different capping ligands.
Publisher: American Chemical Society (ACS)
Date: 03-05-2011
DOI: 10.1021/IC200241D
Abstract: Addition of 1 equiv of potassium metal to a tetrahydrofuran (THF) solution of Zn(2)(4,4'-bipyridine)(mes)(4) (1 mes =2,4,6-Me(3)C(6)H(2)) in the presence of 18-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane) yielded the radical anionic species [Zn(2)(4,4'-bipyridine)(mes)(4)](•-), which was characterized by single crystal X-ray diffraction in [K(18-crown-6)(THF)(2)][Zn(2)(4,4'-bipyridine)(mes)(4)] (2). A similar reaction employing 2 equiv of alkali metal afforded the related complex [K(18-crown-6)](2)[Zn(2)(4,4'-bipyridine)(mes)(4)] (3). The [Zn(2)(4,4'-bipyridine)(mes)(4)](n-) (n = 0-2) moieties present in 1-3 are largely isostructural, yet exhibit significant structural variations which arise because of differences in their electronic structure. These species represent a homologous series of complexes in which the ligand exists in three distinct oxidation states. Structural data, spectroscopic measurements, and density functional theory (DFT) calculations are consistent with the assignment of 1, 2, and 3 as complexes of the neutral, radical anionic, and dianionic 4,4'-bipyridyl ligand, respectively. To the best of our knowledge, species 2 and 3 are the first crystallographically characterized transition metal complexes of the 4,4'-bipyridyl radical and dianion.
Publisher: American Chemical Society (ACS)
Date: 18-08-2011
DOI: 10.1021/JA203320Y
Abstract: A study is presented of the thermodynamics of the halogen-bonding interaction of C(6)F(5)I with a series of structurally similar group 10 metal fluoride complexes trans-[Ni(F)(2-C(5)NF(4))(PCy(3))(2)] (2), trans-[Pd(F)(4-C(5)NF(4))(PCy(3))(2)] (3), trans-[Pt(F){2-C(5)NF(2)H(CF(3))}(PR(3))(2)] (4a, R = Cy 4bR = iPr) and trans-[Ni(F){2-C(5)NF(2)H(CF(3))}(PCy(3))(2)] (5a) in toluene solution. (19)F NMR titration experiments are used to determine binding constants, enthalpies and entropies of these interactions (2.4 ≤ K(300) ≤ 5.2 -25 ≤ ΔH(o) ≤ -16 kJ mol(-1) -73 ≤ ΔS(o) ≤ -49 J K(-1) mol(-1)). The data for -ΔH(o) for the halogen bonding follow a trend Ni < Pd < Pt. The fluoropyridyl ligand is shown to have a negligible influence on the thermodynamic data, but the influence of the phosphine ligand is significant. We also show that the value of the spin-spin coupling constant J(PtF) increases substantially with adduct formation. X-ray crystallographic data for Ni complexes 5a and 5c are compared to previously published data for a platinum analogue. We show by experiment and computation that the difference between Pt-X and Ni-X (X = F, C, P) bond lengths is greatest for X = F, consistent with F(2pπ)-Pt(5dπ) repulsive interactions. DFT calculations on the metal fluoride complexes show the very negative electrostatic potential around the fluoride. Calculations of the enthalpy of adduct formation show energies of -18.8 and -22.8 kJ mol(-1) for Ni and Pt complexes of types 5 and 4, respectively, in excellent agreement with experiment.
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3CC45063E
Abstract: To what extent can a heterometallic chain of transition metal ions generate an asymmetric current-voltage response? Density functional theory suggests that the answer depends very much on the symmetry of the dominant conduction channel: π channels are more localised and hence afford higher rectification ratios.
Publisher: Wiley
Date: 10-2019
DOI: 10.1002/1521-3773(20000901)39:17<3077::AID-ANIE3077>3.0.CO;2-B
Publisher: American Chemical Society (ACS)
Date: 21-11-2013
DOI: 10.1021/IC4018079
Abstract: A series of cobalt complexes of ligands based on the 2-(arylazo)pyridine architecture have been synthesized, and the precise structure and stoichiometry of the complexes depend critically on the identity of substituents in the 2, 4, and 6 positions of the phenyl ring. The 2-(arylazo)pyridine motif can support either Co(II) complexes with neutral ligands, Co(II)Cl2(L(a))2 (1), Co(II)Cl2(L(c))2 (3), [Co(II)Cl(L(b))2]2(PF6)2 (5[PF6]2), or Co(III) complexes of reduced 2-(arylazo)pyridine ligand radical anions, L(•-), Co(III)Cl(L(b•-))2 (2), Co(III)Cl(L(c•-))2 (4), and Co(III)Me(L(b•-))2 (6). All three members of the latter class are based on approximately trigonal-bipyramidal CoX(L(•-))2 architectures [L = 2-(arylazo)pyridine] with two azo nitrogen atoms and the X ligand (X = Cl or Me) in the equatorial plane and two pyridine nitrogen atoms occupying axial positions. Density functional theory suggests that the electronic structure of the Co(III) complexes is also dependent on the identity of X: the strong σ-donor methyl gives a low-spin (S = 0) configuration, while the σ/π-donor chloro gives an intermediate-spin (S = 1) local configuration. In certain cases, one-electron reduction of the Co(II)X2L2 complex leads to the formation of Co(III)X(L(•-))2 i.e., reduction of one ligand induces a further one-electron oxidation of the metal center with concomitant reduction of the second ligand.
Publisher: Informa UK Limited
Date: 23-03-2016
Publisher: Wiley
Date: 13-10-2006
Publisher: Wiley
Date: 13-05-2019
Abstract: We report the characterization of the compound [K([2.2.2]crypt)]
Publisher: Informa UK Limited
Date: 07-07-2022
Publisher: American Chemical Society (ACS)
Date: 06-2001
DOI: 10.1021/JA0038169
Abstract: The isopropyl chloro complex Tp(Me2)NbCl(i-Pr)(PhC&tbd1 CMe) (2) [Tp(Me2) = hydrotris(3,5-dimethylpyrazolyl)borate] exhibits a beta-agostic structure in the crystal. The conformation of the alkyl group is such that the agostic methyl group lies in the Calpha-Nb-Cl plane and the nonagostic one, in a wedge formed by two pyrazole rings. As observed by solution NMR spectroscopy, restricted rotation about the Nb-C bond allows the observation of an equilibrium between this species, 2beta, and a minor alpha-agostic rotamer 2alpha. A putative third rotamer which would have the secondary hydrogen in the wedge is not observed. Similar behavior is observed for related Tp'NbCl(i-Pr)(R(2)C=CMe) [Tp' = Tp(Me2), R(2) = Me (3) Tp' = Tp(Me2,4Cl), R(2) = Ph (4)]. The two diastereomers of the sec-butyl complex Tp(Me2)NbCl(sec-Bu)(MeC=CMe) (5) have been separated. In the crystal, 5CR-AS has a beta-agostic methyl group with the ethyl group located in the wedge formed by two pyrazole rings. The same single beta-agostic species is observed in solution. The other diastereomer, 5AR-CS has a beta-agostic methylene group in the solid state, and the methyl group sits in the wedge. In solution, an equilibrium between this beta-agostic methylene complex 5AR-CSbeta and a minor alpha-agostic species 5AR-CSalpha, where the ethyl substituent of the sec-Bu group is located in the wedge between two pyrazole rings, is observed. NMR techniques have provided thermodynamic parameters for these equilibria (K = 2beta/2alpha = 4.0 +/- 0.1 at 193 K, DeltaG(o)(193) = -2.2 +/- 0.1, DeltaH(o) = -7.4 +/- 0.1 kJ mol(-)(1), and DeltaS(o) = -27 +/- 1 J K(-)(1) mol(-)(1)), as well as kinetic parameters for the rotation about the Nb-C bond (at 193 K, DeltaG(2)= 47.5 +/- 2.5, DeltaH= 58.8 +/- 2.5 kJ mol(-)(1), and DeltaS = 59.0 +/- 10 J K(-)(1) mol(-)(1)). Upon selective deuteration of the beta-methyl protons in Tp(Me2)NbCl[CH(CD(3))(2)](PhC=CMe) (2-d(6)), an expected isotope effect that displaces the equilibrium toward the alpha-agostic rotamer is observed (K = 2-d(6)beta/2-d(6)alpha = 3.1 +/- 0.1 at 193 K, DeltaG(o)(193) = -1.8 +/- 0.1, DeltaH(o) = -8.3 +/- 0.4 kJ mol(-)(1) and DeltaS(o)= -34 +/- 2 J K(-)(1) mol(-)(1)). The anomalous values for DeltaH(o) and DeltaS(o) are discussed. Hybrid quantum mechanics/molecular mechanics calculations (IMOMM (B3LYP:MM3)) on the realistic model Tp(Me2)NbCl(i-Pr)(HC=CMe) have reproduced the energy differences between the alpha- and beta-agostic species with remarkable accuracy. Similar calculations show that Tp(Me2)NbCl(CH(2)Me)(HC=CMe) is alpha-agostic only and that Tp(5)(-)(Me)NbCl(CH(2)Me)(HC=CMe), which has no methyl groups at the 3-positions of the pyrazole rings, is beta-agostic only. Analysis and discussion of the computational and experimental data indicate that the unique behavior observed for the secondary alkyl complexes stems from competition between electronic effects favoring a beta-agostic structure and steric effects directing a bulky substituent in the wedge between two pyrazole rings of Tp(Me2). All of the secondary alkyl complexes thermally rearrange to the corresponding linear alkyl complexes via a first-order reaction.
Publisher: Elsevier BV
Date: 2014
Publisher: Royal Society of Chemistry (RSC)
Date: 1994
DOI: 10.1039/DT9940003759
Publisher: Wiley
Date: 12-06-2012
Publisher: American Chemical Society (ACS)
Date: 12-03-2010
DOI: 10.1021/OM100064Z
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D2SC01748B
Abstract: Two ternary intermetalloid clusters were constructed through binary intermetalloid clusters with a low valent group 12 metal salt. These clusters represent the first ex le of the structural transformation for intermetalloid clusters.
Publisher: Royal Society of Chemistry (RSC)
Date: 2010
DOI: 10.1039/C0CC00187B
Abstract: The persistent radical, [BCl(2)(bipy)](*) (bipy = 2,2'-bipyridyl), has been prepared and characterised by X-ray crystallography, ESR and DFT calculations. The structure is compared with that of the cation, [BCl(2)(bipy)](+).
Publisher: American Chemical Society (ACS)
Date: 04-2004
DOI: 10.1021/JA0396908
Abstract: Density functional theory indicates that oxidative addition of the C-F and C-H bonds in C6F6 and C6H6 at zerovalent nickel and platinum fragments, M(H2PCH2CH2PH2), proceeds via initial exothermic formation of an eta2-coordinated arene complex. Two distinct transition states have been located on the potential energy surface between the eta2-coordinated arene and the oxidative addition product. The first, at relatively low energy, features an eta3-coordinated arene and connects two identical eta2-arene minima, while the second leads to cleavage of the C-X bond. The absence of intermediate C-F or C-H sigma complexes observed in other systems is traced to the ability of the 14-electron metal fragment to accommodate the eta3-coordination mode in the first transition state. Oxidative addition of the C-F bond is exothermic at both nickel and platinum, but the barrier is significantly higher for the heavier element as a result of strong 5dpi-ppi repulsions in the transition state. Similar repulsive interactions lead to a relatively long Pt-F bond with a lower stretching frequency in the oxidative addition product. Activation of the C-H bond is, in contrast, exothermic only for the platinum complex. We conclude that the nickel system is better suited to selective C-F bond activation than its platinum analogue for two reasons: the strong thermodynamic preference for C-F over C-H bond activation and the relatively low kinetic barrier.
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C4QI00038B
Abstract: Using the paramagnetic moment of transition metal ions to tune the transparency of molecule–electrode heterojunctions holds the key to controlling current rectification.
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C4CC06094F
Abstract: We describe the coordination chemistry of the primary phosphine PH 2 C(O)NH 2 (phosphinecarboxamide) to form the novel complexes W(CO) 5 (PH 2 C(O)NH 2 ) ( 1 ) and cis -Mo(CO) 4 (PH 2 C(O)NH 2 ) 2 ( 2 ).
Publisher: Wiley
Date: 17-06-2019
Publisher: Springer Science and Business Media LLC
Date: 31-10-2017
DOI: 10.1038/S41467-017-01301-0
Abstract: Transition-metal oxyhydrides are of considerable current interest due to the unique features of the hydride anion, most notably the absence of valence p orbitals. This feature distinguishes hydrides from all other anions, and gives rise to unprecedented properties in this new class of materials. Here we show via a high-pressure study of anion-ordered strontium vanadium oxyhydride SrVO 2 H that H − is extraordinarily compressible, and that pressure drives a transition from a Mott insulator to a metal at ~ 50 GPa. Density functional theory suggests that the band gap in the insulating state is reduced by pressure as a result of increased dispersion in the ab -plane due to enhanced V dπ -O pπ -V dπ overlap. Remarkably, dispersion along c is limited by the orthogonal V dπ -H 1s -V dπ arrangement despite the greater c -axis compressibility, suggesting that the hydride anions act as π-blockers. The wider family of oxyhydrides may therefore give access to dimensionally reduced structures with novel electronic properties.
Publisher: Wiley
Date: 02-02-2023
Abstract: We report here the synthesis and structural characterization of the first binary iron arsenide cluster anion, [Fe 3 (As 3 ) 3 (As 4 )] 3− , present in both [K([2.2.2]crypt)] 3 [Fe 3 (As 3 ) 3 (As 4 )] ( 1 ) and [K(18 ‐ crown ‐ 6)] 3 [Fe 3 (As 3 ) 3 (As 4 )] ⋅ en ( 2 ). The cluster contains an Fe 3 triangle with three short Fe−Fe bond lengths (2.494(1) Å, 2.459(1) Å and 2.668(2) Å for 1 , 2.471(1) Å, 2.473(1) Å and 2.660(1) Å for 2 ), bridged by a 2‐butene‐like As 4 unit. An analysis of the electronic structure using DFT reveals a triplet ground state with direct Fe−Fe bonds stabilizing the Fe 3 core.
Publisher: American Chemical Society (ACS)
Date: 22-09-2005
DOI: 10.1021/IC050729E
Abstract: The chemical or electrochemical one-electron oxidation of the all-CuII complex [Cu3(mu3-O)(mu-pz)3X3]2- leads to its formally CuII2CuIII analogue (pz = pyrazolato anion X = Cl- and PhCOO-). The X-ray single-crystal structure and density functional theory analysis of the latter agree in revealing the delocalized nature of its mixed-valent Cu3(7+) core.
Publisher: American Chemical Society (ACS)
Date: 14-04-2015
DOI: 10.1021/JA513074M
Abstract: Formaldehyde (HCHO), a strong electrophile and a rapid and reversible inhibitor of hydrogen production by [FeFe]-hydrogenases, is used to identify the point in the catalytic cycle at which a highly reactive metal-hydrido species is formed. Investigations of the reaction of Chlamydomonas reinhardtii [FeFe]-hydrogenase with formaldehyde using pulsed-EPR techniques including electron-nuclear double resonance spectroscopy establish that formaldehyde binds close to the active site. Density functional theory calculations support an inhibited super-reduced state having a short Fe-(13)C bond in the 2Fe subsite. The adduct forms when HCHO is available to compete with H(+) transfer to a vacant, nucleophilic Fe site: had H(+) transfer already occurred, the reaction of HCHO with the Fe-hydrido species would lead to methanol, release of which is not detected. Instead, Fe-bound formaldehyde is a metal-hydrido mimic, a locked, inhibited form analogous to that in which two electrons and only one proton have transferred to the H-cluster. The results provide strong support for a mechanism in which the fastest pathway for H2 evolution involves two consecutive proton transfer steps to the H-cluster following transfer of a second electron to the active site.
Publisher: Elsevier BV
Date: 09-2015
Publisher: Wiley
Date: 27-03-2019
Abstract: The synthesis and characterization of an (arsino)phosphaketene, As(PCO){[N(Dipp)](CH
Publisher: Royal Society of Chemistry (RSC)
Date: 2009
DOI: 10.1039/B907805C
Abstract: A combination of detailed magnetisation studies and electronic-structure analysis using broken-symmetry DFT is used to explore the electronic structure of a trigonal prismatic Cu(II)(6) cluster. The presence of six paramagnetic metal centres with S = 1/2 gives rise to a maximum multiplicity of S = 3 and a total of 31 broken-symmetry states with M(S) < 3. Computed differences in energy between the high-spin and broken-symmetry states are expressed in terms of the 15 distinct Heisenberg exchange coupling parameters, J(ij), and the equations are solved by a least-squares fitting procedure. By inspection of the errors introduced by progressive symmetrisation of the Hamiltonian to reduce the number of independent J(ij), we arrive at a minimal model containing only four distinct J(ij) (three intra- and one inter-triangular). The computed values then guide the fitting of the magnetisation data. The computed trends in J(ij) can only be reproduced when antisymmetric exchange is included in the model Hamiltonian. The use of this Hamiltonian provides a reasonable description of the magnetic behaviour at all temperatures and fields. If a simpler isotropic model Hamiltonian is used instead, the best fit values of J(ij) are compromised by the need to fit the low-temperature region where antisymmetric exchange dominates the shape of the curve.
Publisher: American Chemical Society (ACS)
Date: 14-01-2014
DOI: 10.1021/JA411280V
Abstract: The 12-vertex endohedral cluster [Ru@Ge12](3-) reveals an unprecedented D2d-symmetric 3-connected polyhedral geometry. The structure contrasts dramatically with the known deltahedral or approximately deltahedral geometries of [M@Pb12](2-) (M = Ni, Pd, Pt) and [Mn@Pb12](3-) and is a result of extensive delocalization of electron density from the transition-metal center onto the cage.
Publisher: American Chemical Society (ACS)
Date: 13-02-2018
DOI: 10.1021/ACS.INORGCHEM.8B00026
Abstract: The anion-ordered oxide-hydride SrVO
Publisher: American Chemical Society (ACS)
Date: 03-03-2022
Publisher: Wiley
Date: 02-02-2023
Abstract: We report here the synthesis and structural characterization of the first binary iron arsenide cluster anion, [Fe 3 (As 3 ) 3 (As 4 )] 3− , present in both [K([2.2.2]crypt)] 3 [Fe 3 (As 3 ) 3 (As 4 )] ( 1 ) and [K(18 ‐ crown ‐ 6)] 3 [Fe 3 (As 3 ) 3 (As 4 )] ⋅ en ( 2 ). The cluster contains an Fe 3 triangle with three short Fe−Fe bond lengths (2.494(1) Å, 2.459(1) Å and 2.668(2) Å for 1 , 2.471(1) Å, 2.473(1) Å and 2.660(1) Å for 2 ), bridged by a 2‐butene‐like As 4 unit. An analysis of the electronic structure using DFT reveals a triplet ground state with direct Fe−Fe bonds stabilizing the Fe 3 core.
Publisher: American Chemical Society (ACS)
Date: 03-2022
Publisher: Elsevier BV
Date: 02-2012
Publisher: Wiley
Date: 23-03-2015
Publisher: American Chemical Society (ACS)
Date: 11-04-2012
DOI: 10.1021/JA302096R
Abstract: Formaldehyde-a rapid and reversible inhibitor of hydrogen evolution by [FeFe]-hydrogenases-binds with a strong potential dependence that is almost complementary to that of CO. Whereas exogenous CO binds tightly to the oxidized state known as H(ox) but very weakly to a state two electrons more reduced, formaldehyde interacts most strongly with the latter. Formaldehyde thus intercepts increasingly reduced states of the catalytic cycle, and density functional theory calculations support the proposal that it reacts with the H-cluster directly, most likely targeting an otherwise elusive and highly reactive Fe-hydrido (Fe-H) intermediate.
Publisher: Royal Society of Chemistry (RSC)
Date: 2010
DOI: 10.1039/C0CC01880E
Abstract: The isolation, structural chracterisation and electronic structure of a formally mixed-valent Rh(-I)-Rh(III) complex is described, along with its reaction with dioxygen leading to double arene hydroxylation of the coordinated ligands.
Publisher: MDPI AG
Date: 03-11-2022
DOI: 10.3390/MOLECULES27217544
Abstract: MC-SCF wavefunctions for three endohedral Mn/Si clusters, Mn2Si10, Mn2Si12, and [Mn2Si13]+, show evidence for strong static correlation, both in the Mn-Si bonds (‘in–out correlation’) and between the two Mn centers (‘up–down correlation’). We use both Restricted and Generalized Active Spaces (RAS and GAS) to place constraints on the configurations included in the trial wavefunction, showing that, particularly in the high-symmetry cases, the GAS approach captures more of the static correlation. The important correlating pairs are similar across the series, indicating that the electronic structure of the endohedral Mn2 unit is, to a first approximation, independent of the size of the silicon cage in which it is embedded.
Publisher: Royal Society of Chemistry (RSC)
Date: 2011
DOI: 10.1039/C0DT01221A
Abstract: The electronic structure of so-called 'xenophilic' clusters, which contain both organometallic fragments and Werner-type paramagnetic transition metal centres, presents a challenge to simple theories of bonding. Density functional theory shows clearly that the cluster Mn(2)(thf)(4)(Fe(CO)(4))(2) is best described as an exchange-coupled Mn(II)(2) dimer, the closed-shell organometallic [Fe(CO)(4)](2-) fragments acting simply as bridging ligands. The high-spin configuration of the Mn(II) ions leads to single occupation of the Mn-Fe σ* orbitals and therefore substantially weaker metal-metal bonding than in conventional low-valent organometallic clusters. The transition metal fragments are effective mediators of superexchange (J(calc) = -44 cm(-1)), leading to the measured effective magnetic moment of ~5 μ(B) at 300 K, considerably lower than the limiting value of 8.37 μ(B) for two uncoupled S = 5/2 Mn(II) centres.
Publisher: Elsevier BV
Date: 2013
Publisher: American Chemical Society (ACS)
Date: 19-07-2003
DOI: 10.1021/JA0353053
Abstract: Density functional theory provides new insights into the structural isomerism observed in the cyclopentadienyl-capped iron-sulfur cluster, [(C(5)H(5))(4)Fe(4)S(4)](2+). Two distinct, closely spaced minima have been located, a triplet with D(2) symmetry and a C(2)-symmetric singlet, both of which correspond closely to the structure of one of the known crystal forms of the cation. Thus, the structural ersity in these species reflects genuine molecular bistability rather than simple solid-state packing effects. In contrast, no stable D(2)(d)()-symmetric minimum has been located, suggesting that the reported D(2)(d)() symmetry of the cation in [(C(5)H(5))(4)Fe(4)S(4)][PF(6)](2) may be a crystallographic artifact. In the ruthenium analogue, the more diffuse 4d orbitals stabilize the C(2)-symmetric singlet, which is unambiguously the ground state, but the D(2)-symmetric potential energy surface provides a viable low-energy pathway for the dynamic exchange of the Ru-Ru bonds.
Publisher: American Chemical Society (ACS)
Date: 20-03-2002
DOI: 10.1021/IC010782C
Abstract: Density functional theory is used to probe the reaction of O(2) with the unsaturated transition-metal fragments [M(bipy)(2)](2+), M = Cr, Fe. In both cases, calculations indicate that the O(2) molecule is initially trapped as an eta(2)-bound superoxide ion, where the unpaired electron in the out-of-plane pi orbital of O(2) is weakly coupled to those on the trivalent metal ion. In the chromium case, a cis-dioxo Cr(VI) complex is found to be significantly more stable than the superoxo species. The two minima are, however, separated by a large barrier, along with a change in spin state. For the iron analogue, the relative energies of the two minima are reversed, the superoxo complex being the global minimum. The energetics of the O(2) activation processes are consistent with previously reported mass spectrometric experiments, where an adduct, [M(bipy)(2)(O(2))](2+), was detected only for chromium.
Publisher: American Chemical Society (ACS)
Date: 28-10-2019
DOI: 10.1021/ACS.INORGCHEM.9B02459
Abstract: High-pressure X-ray diffraction measurements on the layered oxyhydrides Sr
Publisher: American Chemical Society (ACS)
Date: 07-03-2018
DOI: 10.1021/ACS.INORGCHEM.7B02620
Abstract: The binary cluster [Co@Sn
Publisher: American Chemical Society (ACS)
Date: 03-2006
DOI: 10.1021/JA0581402
Abstract: The remarkable polymorphism exhibited by the linear tricobalt compounds, Co3(mu3-dpa)4Cl2 and Co3(mu3-dpa)4Br2, can be explained using a model involving three distinct electronic states. At high temperatures, symmetric and unsymmetric forms arise from the population of doublet (2A) and quartet (4B) states, respectively, the latter containing a localized high-spin Co(II) center. In the unsymmetric form, a reduction in temperature leads to a spin-crossover to a second quite distinct doublet state, 2B, where, uniquely, the d(x2-y2) character on the localized Co(II) center is distributed between the occupied and vacant manifolds. The variable population of the Co d(x2-y2) orbital gives rise to the continuous change in Co-Co and Co-N bond lengths as the temperature is decreased.
Publisher: Wiley
Date: 28-12-2017
Abstract: The synthesis and physical properties of two new cationic tri-metallic chains, [(PEt
Publisher: American Chemical Society (ACS)
Date: 27-11-2018
DOI: 10.1021/ACS.INORGCHEM.8B02698
Abstract: The structures of two new oxide chalcogenide phases, Sr
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C9DT03008E
Abstract: A new Zintl cluster, [(Ni@Sn 9 )In(Ni@Sn 9 )] 5− , has been isolated in two distinct isomeric forms, one where both Ni@Sn 9 units are coordinated to the bridging indium atom in an η 3 - mode, the other where one is η 3 - and the other η 4 -.
Publisher: Bioscientifica
Date: 1991
Abstract: Previous studies have indicated that early pregnancy factor (EPF) produced in the pre- and peri-implantation stage of pregnancy appears to consist of inactive components which combine to produce the active species. This is in contrast with EPF produced later in gestation which appears to consist of a single active species. The original studies on ammonium sulphate fractionation of mouse serum and in-vitro culture of mouse ovaries and oviducts have been repeated but tested in the bioassay for EPF, the rosette inhibition test, over an extended range of dilutions. This revealed that the two components in early pregnancy can be understood as EPF and an inhibitor(s). Once this inhibitor is removed, the active fractions in both early and late pregnancy sera exhibit similar behaviour in the above assay. It was shown also that the ovary alone is the source of activity but that this is modulated by an inhibitory substance(s) from the oviduct. Reversed-phase HPLC studies on purified 'early' EPF confirm that active and inhibitory components are present and demonstrate that the active component exhibits an identical elution pattern to 'late' EPF. Thus as pregnancy proceeds, it is not EPF that alters but rather the inhibitor(s), which disappears from the circulation soon after implantation. This substance(s) is under hormonal control, being present during oestrus as well as the early stages of pregnancy it may be an important biological regulator of EPF. Its action in the rosette inhibition test has profound implications for further study using this bioassay.
Publisher: Royal Society of Chemistry (RSC)
Date: 2008
DOI: 10.1039/B804401E
Abstract: A high yield of the tetraphosphaladderene, anti-tetraphosphatricyclo[4.2.0.0(2,5)]octa-3,7-diene, is obtained from reaction of the zirconocene 1,3-diphosphabicyclo[1.1.0]butane with Ph(2)SbCl(3) in THF or CH(2)Cl(2). Exploration of the reaction pathway using density functional theory suggests that an envelope-type adduct of Ph(2)SbCl and 1,3-diphosphabicyclo[1.1.0]butane plays a pivotal role in the reaction. The zwitterionic character of this intermediate species allows it to act simultaneously as both an ene and an eneophile, and a symmetry-allowed bimolecular reaction leads to the tetraphosphaladderene species via a spirocyclic intermediate.
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3CC44990D
Abstract: The radical cation, [1,2-B 2 {1,2-(MeN) 2 C 6 H 4 } 2 ]˙ + , has been prepared and characterised by X-ray crystallography, ESR and DFT calculations.
Publisher: American Chemical Society (ACS)
Date: 10-09-2014
DOI: 10.1021/JA5077525
Abstract: Aromatic hydrogenation is a challenging transformation typically requiring alkali or transition metal reagents and/or harsh conditions to facilitate the process. In sharp contrast, the aromatic heterocycle 2,4,6-tri-tert-butyl-1,3,5-triphosphabenzene is shown to be reduced under 4 atm of H2 to give [3.1.0]bicylo reduction products, with the structure of the major isomer being confirmed by X-ray crystallography. NMR studies show this reaction proceeds via a reversible 1,4-H2 addition to generate an intermediate species, which undergoes an irreversible suprafacial hydride shift concurrent with P-P bond formation to give the isolated products. Further, para-hydrogen experiments confirmed the addition of H2 to triphosphabenzene is a bimolecular process. Density functional theory (DFT) calculations show that facile distortion of the planar triphosphabenzene toward a boat-conformation provides a suprafacial combination of vacant acceptor and donor orbitals that permits this direct and uncatalyzed reduction of the aromatic molecule.
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C5DT03892H
Abstract: The encapsulation of a fluoride ion in a trigonal prismatic CuII6-pyrazolato cage results in a small expansion of the Cu 6 -host.
Publisher: Royal Society of Chemistry (RSC)
Date: 1995
DOI: 10.1039/DT9950002749
Publisher: American Chemical Society (ACS)
Date: 09-1997
DOI: 10.1021/JA964360R
Publisher: American Chemical Society (ACS)
Date: 04-11-2005
DOI: 10.1021/OM050761G
Publisher: Elsevier BV
Date: 10-2003
Publisher: Wiley
Date: 10-2008
Publisher: Elsevier BV
Date: 12-2008
Publisher: American Chemical Society (ACS)
Date: 19-03-2018
DOI: 10.1021/JACS.8B01411
Abstract: Three-coordinate bipyridyl complexes of gold, [(κ
Publisher: American Chemical Society (ACS)
Date: 04-08-2011
DOI: 10.1021/IC200329M
Abstract: Reaction of an ethylenediamine (en) solution of K(4)Pb(9) and 2,2,2-crypt (4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane) with a tetrahydrofuran (THF) solution of Mn(3)(Mes)(6) (Mes = 2,4,6-trimethylphenyl) yielded the anionic cluster [Mn@Pb(12)](3-). This species was observed in the positive and negative ion-mode electrospray mass-spectra of the crude reaction mixture. The crystalline s les obtained from such solutions allowed us to confirm the composition of the s le as [K(2,2,2-crypt)](3)[Mn@Pb(12)]·1.5en (1). Because of numerous issues related to crystal s le quality and crystallographic disorder a high-quality crystal structure solution could not be obtained. Despite this, however, the data collected permit us to draw reasonable conclusions about the charge and connectivity of the [Mn@Pb(12)](3-) cluster anion. Crystals of 1 were further characterized by elemental analysis and electron paramagnetic resonance (EPR). Density Functional Theory (DFT) calculations on such a system reveal a highly distorted endohedral cluster anion, consistent with the structural distortions observed by single crystal X-ray diffraction. The cluster anions are considerably expanded compared to the 36-electron closed-shell analogue [Ni@Pb(12)](2-) and, moreover, exhibit significant low-symmetry distortions from the idealized icosahedral (I(h)) geometry that is characteristic of related endohedral clusters. Our computations indicate that there is substantial transfer of electron density from the formally Mn(-I) center to the low-lying vacant orbitals of the [Pb(12)](2-) cage.
Publisher: American Chemical Society (ACS)
Date: 08-12-2001
DOI: 10.1021/IC0004737
Abstract: Broken-symmetry density functional theory is used to examine the coupling between metal ions in the face-shared bioctahedral complexes M2Cl9(3-), M = Fe, Ru, Os. In the ruthenium and osmium systems, the metal ions have low-spin configurations, and strong coupling results in the formation of a metal-metal sigma bond. In contrast, the iron system contains two weakly coupled high-spin FeIII centers, the different behavior being due to the high spin-polarization energy in the smaller Fe atom. At Fe-Fe separations shorter than 2.4 A, however, an abrupt transition occurs and the ground state becomes very similar to that for the heavier congeners (i.e., strongly coupled low-spin FeIII). The intrinsic link between high-spin/low-spin transitions on the in idual metal centers and the onset of metal-metal bond formation is traced to the spin-polarization energy, which plays a central role in both processes.
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3DT50643F
Abstract: The synthesis of a new endohedral ten-vertex Zintl ion cluster, [Fe@Sn10](3-), isoelectronic with [Fe@Ge10](3-), is reported. In an attempt to place this new cluster within the context of the known structural chemistry of the M@E10 family (M = transition metal, E = main group element), we have carried out a detailed electronic structure analysis of the different structural types: viz bicapped square antiprismatic ([Ni@Pb10](2-), [Zn@In10](8-)), tetra-capped trigonal prismatic ([Ni@In10](10-)) and the remarkable pentagonal prismatic [Fe@Ge10](3-) and [Co@Ge10](3-). We establish that the structural trends can be interpreted in terms of a continuum of effective electron counts at the E10 cage, ranging from electron deficient ( 4n + 2) in [Fe@Ge10](3-). The effective electron count differs from the total valence electron count in that it factors in the increasingly active role of the metal d electrons towards the left of the transition series. The preference for a pentagonal prismatic geometry in [Fe@Ge10](3-) emerges as a natural consequence of backbonding to the cage from four orthogonal 3d orbitals of the low-valent metal ion. Our calculations suggest that the new [Fe@Sn10](3-) cluster should also exhibit structural consequences of backbonding from the metal to the cage, albeit to a less extreme degree than in its Ge analogue. The global minimum lies on a very flat surface connecting D4d, C2v and C3v-symmetric minima, suggesting a very plastic structure that may be easily deformed by the surrounding crystal environment. If so, then this provides a new and quite distinct structural type for the M@E10 family.
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Start Date: 2009
End Date: 2009
Funder: Engineering and Physical Sciences Research Council
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Funder: Engineering and Physical Sciences Research Council
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Funder: Engineering and Physical Sciences Research Council
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Funder: Engineering and Physical Sciences Research Council
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