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Robert Stranger - One of the best experts on this subject based on the ideXlab platform.
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Metal-Metal Bonding in Trinuclear, Mixed-Valence [Ti3X12]4- (X = F, Cl, Br, I) Face-Shared Complexes
Inorganic chemistry, 2015Co-Authors: Jinasena W. Hewage, Germán Cavigliasso, Robert StrangerAbstract:Metal-Metal Bonding in structurally characterized In4Ti3Br12, comprising linear, mixed-valence d(1)d(2)d(1) face-shared [Ti3Br12](4-) units with a Ti-Ti separation of 3.087 A and strong antiferromagnetic coupling (Θ = -1216 K), has been investigated using density functional theory. The antiferromagnetic configuration, in which the single d electron on each terminal Ti(III) (d(1)) metal center is aligned antiparallel to the two electrons occupying the central Ti(II) (d(2)) metal site, is shown to best agree with the reported structural and magnetic data and is consistent with an S = 0 ground state in which two of the four metal-based electrons are involved in a two-electron, three-center σ bond between the Ti atoms (formal Ti-Ti bond order of ∼0.5). However, the unpaired spin densities on the Ti sites indicate that while the Metal-Metal σ interaction is strong, the electrons are not fully paired off and consequently dominate the ground state antiferromagnetic coupling. The same overall partially delocalized Bonding regime is predicted for the other three halide [Ti3X12](4-) (X = F, Cl, I) systems with the Metal-Metal Bonding becoming weaker as the halide group is descended. The possibility of bond-stretch isomerism was also examined where one isomer has a symmetric structure with identical Ti-Ti bonds while the other is unsymmetric with one short and one long Ti-Ti bond. Although calculations indicate that the latter form is more stable, the barrier to interconversion between equivalent unsymmetric forms, where the short Ti-Ti bond is on one side of the trinuclear unit or the other, is relatively small such that at room temperature only the averaged (symmetric) structure is likely to be observed.
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Periodic trends in metal–metal Bonding in edge-shared [M2Cl10]4− systems
Polyhedron, 2007Co-Authors: Germán Cavigliasso, Robert StrangerAbstract:Abstract Periodic trends in metal–metal interactions in edge-shared [M 2 Cl 10 ] 4− systems, involving the transition metals from groups 4 through 8 and electronic configurations ranging from d 1 d 1 through d 5 d 5 , have been investigated by calculating metal–metal Bonding and spin-polarization (exchange) effects using density functional theory. The trends found in this study are compared with those for the analogous face-shared [M 2 Cl 9 ] 3− systems reported in earlier work. Strong linear correlations between the metal–metal Bonding and spin-polarization terms have been obtained for all groups considered. In general, spin polarization and electron localization are predominant in 3d–3d species whereas electron delocalization and metal–metal Bonding are favoured in 5d–5d species, with more variable results observed for 4d–4d systems. As previously found for face-shared [M 2 Cl 9 ] 3− systems, the strong correlations between the metal–metal Bonding and spin polarization energy terms can be related to the fact that both properties appear to be similarly affected by the changes in the metal orbital properties and electron density occurring within the d n d n groups. A significant difference between the face-shared and edge-shared systems is that while the 4d metals in the former show a strong tendency for delocalized metal–metal bonded structures, the edge-shared counterparts display much greater variation with both metal–metal bonded and weakly coupled complexes observed. The tendency for weaker metal–metal interactions can be traced to the inability of the edge-shared bridging structure to accommodate the smaller metal–metal distances required for strong metal–metal Bonding.
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Ligand dependence of Metal-Metal Bonding in the d(3)d(3) dimers M(2)X(9)(n-) (M(III) = Cr, Mo, W; M(IV) = Mn, Tc, Re; X = F, Cl, Br, I).
Inorganic chemistry, 2001Co-Authors: Robert Stranger, And Alison Turner, Christopher D. DelfsAbstract:The ligand dependence of metal−metal Bonding in the d3d3 face-shared M2X9n- (MIII = Cr, Mo, W; MIV = Mn, Tc, Re; X = F, Cl, Br, I) dimers has been investigated using density functional theory. In general, significant differences in metal−metal Bonding are observed between the fluoride and chloride complexes involving the same metal ion, whereas less dramatic changes occur between the bromide and iodide complexes and minimal differences between the chloride and bromide complexes. For M = Mo, Tc, and Re, change in the halide from F to I results in weaker metal−metal Bonding corresponding to a shift from either the triple metal−metal bonded to single bonded case or from the latter to a nonbonded structure. A fragment analysis performed on M2X93- (M = Mo, W) allowed determination of the metal−metal and metal-bridge contributions to the total Bonding energy in the dimer. As the halide changes from F to I, there is a systematic reduction in the total interaction energy of the fragments which can be traced to a ...
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Metal−Metal Bonding in M2Cl6(H2PCH2PH2)2, M2Cl6(PH3)4, and M2Cl104- (M = Cr, Mo, W) Edge-Shared Dimer Systems
Inorganic chemistry, 1999Co-Authors: Robert Stranger, Timothy Lovell, John E. McgradyAbstract:Density functional theory is used to determine the electronic structures, geometries, and periodic trends in Metal-Metal Bonding in the homo- and heterobimetallic d(3)d(3) edge-shared systems M(2)Cl(10)(4-), M(2)Cl(6)(PH(3))(4), and M(2)Cl(6)(H(2)PCH(2)PH(2))(2) (M = Cr, Mo, W). The much shorter Metal-Metal distances in these complexes relative to M(2)Cl(10)(4-) (M = Mo, W) are shown to arise solely from electronic differences between chlorine and phosphine donors. Due to inversion of the delta and delta orbitals, the complexes M(2)Cl(6)(PH(3))(4) and M(2)Cl(6)(H(2)PCH(2)PH(2))(2) (M = Mo, W) are found to possess formal Metal-Metal double bonds. The periodic trends in Metal-Metal Bonding in these systems are rationalized in terms of the energetic contributions of orbital overlap (DeltaE(ovlp)) and spin polarization (DeltaE(spe)). The reduction in DeltaE(spe) and increase in DeltaE(ovlp) on replacement of axial chlorides with phosphine both favor stronger Metal-Metal Bonding in the phosphine-based complexes. The strong linear dependence observed between DeltaE(spe) and DeltaE(ovlp) enables the Metal-Metal Bonding in these systems to be predicted simply from single-ion spin-polarization energies. The antiferromagnetic coupling in M(2)Cl(6)(H(2)PCH(2)PH(2))(2) (M = Mo, W) and MoWCl(6)(H(2)PCH(2)PH(2))(2) is shown to be mostly due to coupling of the metal delta electrons, with a smaller contribution from the pi electrons, particularly for the dimolybdenum complex.
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Metal−Metal Bonding in d1d1 and d2d2 Bioctahedral Dimer Systems: A Density Functional Study of Face-Shared M2X93- (M = Ti, Zr, Hf, V, Nb, Ta) Complexes
Inorganic chemistry, 1998Co-Authors: Robert Stranger, John E. Mcgrady, Timothy LovellAbstract:Density functional theory is used to investigate the electronic and geometric structures and periodic trends in metal−metal Bonding of d1d1 and d2d2 face-shared M2X93- dimers of Ti, Zr, Hf (d1d1) and V, Nb, Ta (d2d2). For these systems three distinct coupling modes can be recognized, depending on the occupation of the trigonal t2g(a1 + e) single-ion orbitals, which determine the ground-state geometry and extent of metal−metal Bonding. For Ti2Cl93-, the [a1 × a1] broken-symmetry optimized structure, corresponding to significant delocalization of the metal-based σ electrons, nicely rationalizes the strong antiferromagnetic coupling reported for Cs3Ti2Cl9. The ground-state geometries for Zr2Cl93- and Hf2Cl93- correspond to complete delocalization of the metal-based electrons in a metal−metal σ bond. For V2Cl93-, the global minimum is found to be the ferromagnetic [a1e × e2] spin-quintet state giving rise to a long V−V separation, consistent with the known structure and reported weak ferromagnetic behavior of...
John E. Mcgrady - One of the best experts on this subject based on the ideXlab platform.
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exchange coupling through diamagnetic fe co 4 2 bridging ligands in a xenophilic cluster
Dalton Transactions, 2011Co-Authors: Tobias Kramer, Zhenyang Lin, John E. McgradyAbstract: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 Mn2(thf)4(Fe(CO)4)2 is best described as an exchange-coupled MnII2 dimer, the closed-shell organometallic [Fe(CO)4]2− fragments acting simply as bridging ligands. The high-spin configuration of the MnII 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 (Jcalc = −44 cm−1), leading to the measured effective magnetic moment of ∼5 μB at 300 K, considerably lower than the limiting value of 8.37 μB for two uncoupled S = 5/2 MnII centres.
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The interplay between steric repulsions and metal–metal Bonding in [Ru2(μ-Cl)3(PR3)6]z+, R = H, Me, Et, z = 1, 2, 3: a hybrid QM/MM study
Dalton Transactions, 2002Co-Authors: Sushilla Z. Knottenbelt, John E. Mcgrady, Graham A. HeathAbstract:The hybrid quantum/molecular mechanics methodology is used to examine the interplay between metal–metal Bonding and steric effects in a series of isostructural redox-related ruthenium dimers. Potential energy surfaces for the various electronic states arising from (d6d6) (1+), (d5d6) (2+) and (d5d5) (3+) configurations are explored. Somewhat counterintuitively, the bulky groups on the phosphine ligands are found to have most effect when the Ru–Ru Bonding is strongest. The origin of this trend has been traced to the nature of the steric interactions, which are largely between the bridging halides and the substituents on the phosphine. As the Ru–Ru bond contracts, a concertina-like motion displaces the halides away from the trigonal axis and towards the phosphine substituents. The resulting competition between Ru–Ru Bonding and steric repulsions means that varying the bulk of the phosphine provides an efficient mechanism for tuning or even completely eliminating the metal–metal bond.
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Metal−Metal Bonding in M2Cl6(H2PCH2PH2)2, M2Cl6(PH3)4, and M2Cl104- (M = Cr, Mo, W) Edge-Shared Dimer Systems
Inorganic chemistry, 1999Co-Authors: Robert Stranger, Timothy Lovell, John E. McgradyAbstract:Density functional theory is used to determine the electronic structures, geometries, and periodic trends in Metal-Metal Bonding in the homo- and heterobimetallic d(3)d(3) edge-shared systems M(2)Cl(10)(4-), M(2)Cl(6)(PH(3))(4), and M(2)Cl(6)(H(2)PCH(2)PH(2))(2) (M = Cr, Mo, W). The much shorter Metal-Metal distances in these complexes relative to M(2)Cl(10)(4-) (M = Mo, W) are shown to arise solely from electronic differences between chlorine and phosphine donors. Due to inversion of the delta and delta orbitals, the complexes M(2)Cl(6)(PH(3))(4) and M(2)Cl(6)(H(2)PCH(2)PH(2))(2) (M = Mo, W) are found to possess formal Metal-Metal double bonds. The periodic trends in Metal-Metal Bonding in these systems are rationalized in terms of the energetic contributions of orbital overlap (DeltaE(ovlp)) and spin polarization (DeltaE(spe)). The reduction in DeltaE(spe) and increase in DeltaE(ovlp) on replacement of axial chlorides with phosphine both favor stronger Metal-Metal Bonding in the phosphine-based complexes. The strong linear dependence observed between DeltaE(spe) and DeltaE(ovlp) enables the Metal-Metal Bonding in these systems to be predicted simply from single-ion spin-polarization energies. The antiferromagnetic coupling in M(2)Cl(6)(H(2)PCH(2)PH(2))(2) (M = Mo, W) and MoWCl(6)(H(2)PCH(2)PH(2))(2) is shown to be mostly due to coupling of the metal delta electrons, with a smaller contribution from the pi electrons, particularly for the dimolybdenum complex.
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Metal−Metal Bonding in d1d1 and d2d2 Bioctahedral Dimer Systems: A Density Functional Study of Face-Shared M2X93- (M = Ti, Zr, Hf, V, Nb, Ta) Complexes
Inorganic chemistry, 1998Co-Authors: Robert Stranger, John E. Mcgrady, Timothy LovellAbstract:Density functional theory is used to investigate the electronic and geometric structures and periodic trends in metal−metal Bonding of d1d1 and d2d2 face-shared M2X93- dimers of Ti, Zr, Hf (d1d1) and V, Nb, Ta (d2d2). For these systems three distinct coupling modes can be recognized, depending on the occupation of the trigonal t2g(a1 + e) single-ion orbitals, which determine the ground-state geometry and extent of metal−metal Bonding. For Ti2Cl93-, the [a1 × a1] broken-symmetry optimized structure, corresponding to significant delocalization of the metal-based σ electrons, nicely rationalizes the strong antiferromagnetic coupling reported for Cs3Ti2Cl9. The ground-state geometries for Zr2Cl93- and Hf2Cl93- correspond to complete delocalization of the metal-based electrons in a metal−metal σ bond. For V2Cl93-, the global minimum is found to be the ferromagnetic [a1e × e2] spin-quintet state giving rise to a long V−V separation, consistent with the known structure and reported weak ferromagnetic behavior of...
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Electronic Structure of [Pt2(μ-O2CCH3)4(H2O)2]2+ Using the Quasi-Relativistic Xα−SW Method: Analysis of Metal−Metal Bonding, Assignment of Electronic Spectra, and Comparison with Rh2(μ-O2CCH3)4(H2O)2
Inorganic chemistry, 1996Co-Authors: Robert Stranger, John E. Mcgrady, Gregory A. Medley, Jodie M. Garrett, Trevor G. AppletonAbstract:The electronic structure and metal−metal Bonding in the classic d7d7 tetra-bridged lantern dimer [Pt2(O2CCH3)4(H2O)2]2+ has been investigated by performing quasi-relativistic Xα−SW molecular orbital calculations on the analogous formate-bridged complex. From the calculations, the highest occupied and lowest unoccupied metal-based levels are δ*(Pt2) and σ*(Pt2), respectively, indicating a metal−metal single bond analogous to the isoelectronic Rh(II) complex. The energetic ordering of the main metal−metal Bonding levels is, however, quite different from that found for the Rh(II) complex, and the upper metal−metal Bonding and antiBonding levels have significantly more ligand character. As found for the related complex [W2(O2CH)4], the inclusion of relativistic effects leads to a further strengthening of the metal−metal σ bond as a result of the increased involvement of the higher-lying platinum 6s orbital. The low-temperature absorption spectrum of [Pt2(O2CCH3)4(H2O)2]2+ is assigned on the basis of Xα−SW cal...
Connie C Lu - One of the best experts on this subject based on the ideXlab platform.
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configuring bonds between first row transition metals
Accounts of Chemical Research, 2015Co-Authors: Reed J Eisenhart, Laura J Clouston, Connie C LuAbstract:ConspectusAlfred Werner, who pioneered the field of coordination chemistry, envisioned coordination complexes as a single, transition metal atom at the epicenter of a vast ligand space. The idea that the locus of a coordination complex could be shared by multiple metals held together with covalent bonds would eventually lead to the discovery of the quadruple and quintuple bond, which have no analogues outside of the transition metal block. Metal–metal Bonding can be classified into homometallic and heterometallic groups. Although the former is dominant, the latter is arguably more intriguing because of the inherently larger chemical space in which metal–metal Bonding can be explored.In 2013, Lu and Thomas independently reported the isolation of heterometallic multiple bonds with exclusively first-row transition metals. Structural and theoretical data supported triply bonded Fe–Cr and Fe–V cores. This Account describes our continued efforts to configure bonds between first-row transition metals from titani...
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Systematic Variation of Metal–Metal Bond Order in Metal–Chromium Complexes
Journal of the American Chemical Society, 2013Co-Authors: Laura J Clouston, Randall B. Siedschlag, P. Alex Rudd, Nora Planas, Shuxian Hu, Adam D. Miller, Laura Gagliardi, Connie C LuAbstract:In the field of metal–metal Bonding, the occurrence of stable, multiple bonds between different transition metals is uncommon, and is largely unknown for different first-row metals. Adding to a recently reported iron–chromium complex, three additional M–Cr complexes have been isolated, where the iron site is systematically replaced with other first-row transition metals (Mn, Co, or Ni), while the chromium site is kept invariant. These complexes have been characterized by X-ray crystallography. The Mn–Cr complex has an ultrashort metal–metal bond distance of 1.82 A, which is consistent with a quintuple bond. The M–Cr bond distances increases across the period from M = Mn to M = Ni, as the formal bond order decreases from 5 to 1. Theoretical calculations reveal that the M–Cr bonds become increasingly polarized across the period. We propose that these trends arise from increasing differences in the energies and/or contraction of the metals’ d-orbitals (M vs Cr). The cyclic voltammograms of these heterobimeta...
Laura J Clouston - One of the best experts on this subject based on the ideXlab platform.
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configuring bonds between first row transition metals
Accounts of Chemical Research, 2015Co-Authors: Reed J Eisenhart, Laura J Clouston, Connie C LuAbstract:ConspectusAlfred Werner, who pioneered the field of coordination chemistry, envisioned coordination complexes as a single, transition metal atom at the epicenter of a vast ligand space. The idea that the locus of a coordination complex could be shared by multiple metals held together with covalent bonds would eventually lead to the discovery of the quadruple and quintuple bond, which have no analogues outside of the transition metal block. Metal–metal Bonding can be classified into homometallic and heterometallic groups. Although the former is dominant, the latter is arguably more intriguing because of the inherently larger chemical space in which metal–metal Bonding can be explored.In 2013, Lu and Thomas independently reported the isolation of heterometallic multiple bonds with exclusively first-row transition metals. Structural and theoretical data supported triply bonded Fe–Cr and Fe–V cores. This Account describes our continued efforts to configure bonds between first-row transition metals from titani...
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Systematic Variation of Metal–Metal Bond Order in Metal–Chromium Complexes
Journal of the American Chemical Society, 2013Co-Authors: Laura J Clouston, Randall B. Siedschlag, P. Alex Rudd, Nora Planas, Shuxian Hu, Adam D. Miller, Laura Gagliardi, Connie C LuAbstract:In the field of metal–metal Bonding, the occurrence of stable, multiple bonds between different transition metals is uncommon, and is largely unknown for different first-row metals. Adding to a recently reported iron–chromium complex, three additional M–Cr complexes have been isolated, where the iron site is systematically replaced with other first-row transition metals (Mn, Co, or Ni), while the chromium site is kept invariant. These complexes have been characterized by X-ray crystallography. The Mn–Cr complex has an ultrashort metal–metal bond distance of 1.82 A, which is consistent with a quintuple bond. The M–Cr bond distances increases across the period from M = Mn to M = Ni, as the formal bond order decreases from 5 to 1. Theoretical calculations reveal that the M–Cr bonds become increasingly polarized across the period. We propose that these trends arise from increasing differences in the energies and/or contraction of the metals’ d-orbitals (M vs Cr). The cyclic voltammograms of these heterobimeta...
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systematic variation of metal metal bond order in metal chromium complexes
Journal of the American Chemical Society, 2013Co-Authors: Laura J Clouston, Randall B. Siedschlag, Nora Planas, Adam D. Miller, Alex P Rudd, Laura GagliardiAbstract:In the field of metal–metal Bonding, the occurrence of stable, multiple bonds between different transition metals is uncommon, and is largely unknown for different first-row metals. Adding to a recently reported iron–chromium complex, three additional M–Cr complexes have been isolated, where the iron site is systematically replaced with other first-row transition metals (Mn, Co, or Ni), while the chromium site is kept invariant. These complexes have been characterized by X-ray crystallography. The Mn–Cr complex has an ultrashort metal–metal bond distance of 1.82 A, which is consistent with a quintuple bond. The M–Cr bond distances increases across the period from M = Mn to M = Ni, as the formal bond order decreases from 5 to 1. Theoretical calculations reveal that the M–Cr bonds become increasingly polarized across the period. We propose that these trends arise from increasing differences in the energies and/or contraction of the metals’ d-orbitals (M vs Cr). The cyclic voltammograms of these heterobimeta...
Timothy Lovell - One of the best experts on this subject based on the ideXlab platform.
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Metal−Metal Bonding in M2Cl6(H2PCH2PH2)2, M2Cl6(PH3)4, and M2Cl104- (M = Cr, Mo, W) Edge-Shared Dimer Systems
Inorganic chemistry, 1999Co-Authors: Robert Stranger, Timothy Lovell, John E. McgradyAbstract:Density functional theory is used to determine the electronic structures, geometries, and periodic trends in Metal-Metal Bonding in the homo- and heterobimetallic d(3)d(3) edge-shared systems M(2)Cl(10)(4-), M(2)Cl(6)(PH(3))(4), and M(2)Cl(6)(H(2)PCH(2)PH(2))(2) (M = Cr, Mo, W). The much shorter Metal-Metal distances in these complexes relative to M(2)Cl(10)(4-) (M = Mo, W) are shown to arise solely from electronic differences between chlorine and phosphine donors. Due to inversion of the delta and delta orbitals, the complexes M(2)Cl(6)(PH(3))(4) and M(2)Cl(6)(H(2)PCH(2)PH(2))(2) (M = Mo, W) are found to possess formal Metal-Metal double bonds. The periodic trends in Metal-Metal Bonding in these systems are rationalized in terms of the energetic contributions of orbital overlap (DeltaE(ovlp)) and spin polarization (DeltaE(spe)). The reduction in DeltaE(spe) and increase in DeltaE(ovlp) on replacement of axial chlorides with phosphine both favor stronger Metal-Metal Bonding in the phosphine-based complexes. The strong linear dependence observed between DeltaE(spe) and DeltaE(ovlp) enables the Metal-Metal Bonding in these systems to be predicted simply from single-ion spin-polarization energies. The antiferromagnetic coupling in M(2)Cl(6)(H(2)PCH(2)PH(2))(2) (M = Mo, W) and MoWCl(6)(H(2)PCH(2)PH(2))(2) is shown to be mostly due to coupling of the metal delta electrons, with a smaller contribution from the pi electrons, particularly for the dimolybdenum complex.
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Metal−Metal Bonding in d1d1 and d2d2 Bioctahedral Dimer Systems: A Density Functional Study of Face-Shared M2X93- (M = Ti, Zr, Hf, V, Nb, Ta) Complexes
Inorganic chemistry, 1998Co-Authors: Robert Stranger, John E. Mcgrady, Timothy LovellAbstract:Density functional theory is used to investigate the electronic and geometric structures and periodic trends in metal−metal Bonding of d1d1 and d2d2 face-shared M2X93- dimers of Ti, Zr, Hf (d1d1) and V, Nb, Ta (d2d2). For these systems three distinct coupling modes can be recognized, depending on the occupation of the trigonal t2g(a1 + e) single-ion orbitals, which determine the ground-state geometry and extent of metal−metal Bonding. For Ti2Cl93-, the [a1 × a1] broken-symmetry optimized structure, corresponding to significant delocalization of the metal-based σ electrons, nicely rationalizes the strong antiferromagnetic coupling reported for Cs3Ti2Cl9. The ground-state geometries for Zr2Cl93- and Hf2Cl93- correspond to complete delocalization of the metal-based electrons in a metal−metal σ bond. For V2Cl93-, the global minimum is found to be the ferromagnetic [a1e × e2] spin-quintet state giving rise to a long V−V separation, consistent with the known structure and reported weak ferromagnetic behavior of...