Magnetic coupling and intermetallic electron transfer in the heterodinuclear bioctahedral complexes MW(III)Cl(9)(n-) (M = V(II), Cr(III), Mn(IV)): tweaking the balance between ferromagnetism and antiferromagnetism

DFT study on magnetic interaction in an orbitally degenerate Ti3+ dimer complex

The magnetic interaction in an orbitally degenerate transition metal dimer complex is investigated using a typical example of a d(1)-d(1) dimer complex, the Ti2Cl9(3-) cluster. The local orbital functions are defined by linear combinations of the molecular orbital functions which are calculated by density functional theory (DFT). In the DFT calculation, the Perdew-Burke-Ernzerhof (PBE) functional and hybrid PBE0 functional are utilized. The matrix elements of the effective Hamiltonian of the d-electrons are evaluated by the DFT calculation except for one parameter which is determined by comparing the zero-temperature magnetic susceptibility in the direction along the c axis χ(∥) with the experimental result. By the calculation with the PBE0 functional, the zero-temperature magnetic susceptibility in the perpendicular direction χ(⊥) and the temperature dependence of the susceptibilities in both directions agree with the experiment. On the other hand, by the calculation with the PBE functional, χ(⊥) is smaller than the experimental values because the on-site potential is underestimated.

Isolation, characterization, and computational studies of the novel [Mo3(mu3-Br)2(mu-Br)3Br6]2- cluster anion

The novel trimolybdenum cluster [Mo(3)(mu(3)-Br)(2)(mu-Br)(3)Br(6)](2-) (1, {Mo(3)}(9+), 9 d-electrons) has been isolated from the reaction of [Mo(CO)(6)] with 1,2-C(2)H(4)Br(2) in refluxing PhCl. The compound has been characterized in solution by electrospray ionization mass spectrometry (ESI-MS), UV-vis spectroscopy, cyclic voltammetry, and in the solid state by X-ray analysis (counter-cations: (n-Bu)(4)N(+) (1), Et(4)N(+), Et(3)BzN(+)), electron paramagnetic resonance (EPR), magnetic susceptibility measurements, and infrared spectroscopy. The least disordered (n-Bu)(4)N(+) salt crystallizes in the monoclinic space group C2/c, a = 20.077(2) A, b = 11.8638(11) A, c = 22.521(2) A, alpha = 90 deg, beta = 109.348(4) deg, gamma = 90 deg, V = 5061.3(9) A(3), Z = 4 and contains an isosceles triangular metal arrangement, which is capped by two bromine ligands. Each edge of the triangle is bridged by bromine ions. The structure is completed by six terminal bromine ligands. According to the magnetic measurements and the EPR spectrum the trimetallic core possesses one unpaired electron. Electrochemical data show that oxidation by one electron of 1 is reversible, thus proceeding with retention of the trimetallic core, while the reduction is irreversible. The effective magnetic moment of 1 (mu(eff), 1.55 mu(B), r.t.) is lower than the spin-only value (1.73 mu(B)) for S = 1/2 systems, most likely because of high spin-orbit coupling of Mo(III) and/or magnetic coupling throughout the lattice. The ground electronic state of 1 was studied using density functional theory techniques under the broken symmetry formalism. The ground state is predicted to exhibit strong antiferromagnetic coupling between the three molybdenum atoms of the core. Moreover, our calculated data predict two broken symmetry states that differ only by 0.4 kcal/mol (121 cm(-1)). The antiferromagnetic character is delocalized over three magnetic orbitals populated by three electrons. The assignment of the infrared spectra is also provided.

Even-Numbered Metal Chain Complexes: Synthesis, Characterization, and DFT Analysis of [Ni4(μ4-Tsdpda)4(H2O)2] (Tsdpda2- = N-(p-toluenesulfonyl)dipyridyldiamido), [Ni4(μ4-Tsdpda)4]+, and Related Ni4 String Complexes

The synthesis and the X-ray structure of two complexes exhibiting a linear chain of four nickel atoms is reported, following Ni4(mu4-phdpda)4 (1), which had been characterized previously. [Ni4(mu4-Tsdpda)4(H2O)2], where H2Tsdpda is N-(p-toluenesulfonyl)dipyridyldiamine (2), is axially coordinated to two water molecules, at variance with 1. One-electron oxidation of 2 resulted in the loss of the axial ligands, yielding [Ni4(mu4-Tsdpda)4]+, [3]+, which was also structurally characterized. Finally, we report the structure of Ni4(mu4-DAniDANy)4 (4), a complex synthesized starting from the new ligand N,N'-bis-p-anisyl-2,7-diamino-1,8-naphthyridine. Magnetic measurements concluded that 4 is diamagnetic, like 1, whereas 2 is antiferromagnetic (-2J(14) = 80 cm(-)(1), using the Heisenberg Hamiltonian H = -2J(14) S(1).S(4)), as are other axially coordinated chains with an odd number of nickel atoms. DFT calculations are reported on these complexes in order to rationalize their electronic structure and their magnetic behavior. The magnetic properties of the [Ni4]8+ complexes are governed by the electronic state of the Ni(II) atoms, which may be either low-spin (S = 0), or high-spin (S = 1). DFT calculations show that the promotion to high spin of two Ni atoms in the chain, either external or internal, depends on the interplay between axial and equatorial coordination. The synergy between axial coordination and the presence of electron-withdrawing toluenesulfonyl substituents in 2 favors the promotion to the high-spin state of the terminal Ni atoms, thus yielding an antiferromagnetic ground state for the complex. This is at variance with complexes 1 and 4, for which the lowest quintet state results from the promotion to high spin of the internal nickel atoms, together with an important ligand participation, and is destabilized by 9 to 16 kcal mol(-1) with respect to the diamagnetic ground state.

Structure and Magnetism of [M3]6/7+ Metal Chain Complexes from Density Functional Theory: Analysis for Copper and Predictions for Silver

The ground-state electronic structure of the trinuclear complex Cu3(dpa)4Cl2 (1), where dpa is the anion of di(2-pyridyl)amine, has been investigated within the framework of density functional theory (DFT) and compared with that obtained for other known M3(dpa)4Cl2 complexes (M = Cr, Co, Ni) and for the still hypothetical Ag3(dpa)4Cl2 compound. Both coinage metal compounds display three singly occupied x2-y2-like (delta) orbitals oriented toward the nitrogen environment of each metal atom, generating antibonding M-(N4) interactions. All other metal orbital combinations are doubly occupied, resulting in no delocalized metal-metal bonding. This is at variance with the other known symmetric M3(dpa)4Cl2 complexes of the first transition series, which all display some delocalized bonding through the metal backbone, with formal bond multiplicity decreasing in the order Cr > Co > Ni. An antiferromagnetic coupling develops between the singly occupied MOs via a superexchange mechanism involving the bridging dpa ligands. This magnetic interaction can be considered as an extension to the three aligned Cu(II) atoms of the well-documented exchange coupling observed in carboxylato-bridged dinuclear copper compounds. Broken-symmetry calculations with approximate spin projection adequately reproduce the coupling constant observed for 1. Oxidation of 1 removes an electron from the magnetic orbital located on the central Cu atom and its ligand environment; 1+ displays a much weaker antiferromagnetic interaction coupling the terminal Cu-N4 moieties via four ligand pathways converging through the x2-y2 orbital of the central metal. The silver homologues of 1 and 1+ display similar electronic ground states, but the calculated magnetic couplings are stronger by factors of about 3 and 4, respectively, resulting from a better overlap between the metal centers and their equatorial ligand environment within the magnetic orbitals.

Theoretical Investigation of Intramolecular Magnetic Interaction through an Ethylenic Coupler

We show that an ethylenic coupler provides a very strong intramolecular magnetic interaction. A recently synthesized nitronyl nitroxide derivative, D-NIT2, is investigated by ab initio quantum chemical methods. The broken symmetry approach yields a coupling constant -541 K that is in good agreement with the observed value in solid state.

Electron Delocalization in Nickel Metallic Wires: A DFT Investigation of Ni3(dpa)4Cl2 and [Ni3(dpa)4]3+ (dpa = Dipyridylamide) and Extension to Higher Nuclearity Chains

The electronic structure of Ni(3)(dpa)(4)Cl(2) (1) has been investigated within the framework of the density functional theory (DFT), using two types of exchange-correlation functionals and various basis sets. The "broken-symmetry" approach proposed by Noodleman for the characterization of electronic states displaying an antiferromagnetic coupling has been applied to 1. All calculations lead to the conclusion that the ground state results from an antiferromagnetic coupling between the terminal Ni atoms, both displaying a high-spin electronic configuration. The central Ni atom is in a low-spin configuration, but is involved in a superexchange interaction connecting the two magnetic centers. These results are in agreement with the assignments recently proposed by the group of F. A. Cotton on the basis of magnetic measurements. It is shown that the ground state electronic configuration calculated for 1 provides the trinickel framework with some delocalized sigma bonding character. The observed geometry of 1 is accurately reproduced by the broken-symmetry solution. The doublet ground state assigned to the oxidized species [Ni(3)(dpa)(4)](3+) (2) and the dramatic contraction of the coordination sphere of the terminal metals observed upon oxidation are also confirmed by the calculations. However, the formal Ni-Ni bond order is not expected to increase in the oxidized species. The contraction of the Ni-Ni distance in 2 is shown to result in part from the vanishing of the important trans influence originating in the axial ligands, and for the rest from a more efficient shielding of the metal nuclear charge along the Ni-Ni-Ni axis. The conclusions deduced from the analysis of the bonding in 1 and 2 can be extended to their homologues with higher nuclearity. More specifically, it is predicted that the single occupancy of the most antibonding sigma orbital, extending over the whole metal framework, will provide the (Ni(p))(2)(p)(/(2)(p)(+1)+) chains with some delocalized bonding character and, possibly, with electrical conduction properties.

Cl(3)V(mu-S(CH(3))(2))(3)VCl(3)(2)(-): a first-row, face-shared bioctahedral complex with multiple metal-metal bonding

Density functional theory calculations have been used to investigate the structure and bonding of the d(3)d(3) bioctahedral complexes X(3)V(mu-S(CH(3))(2))(3)VX(3)(2)(-) (X = F(-), Cl(-), OH(-), SH(-), NH(2)(-)). According to geometry optimizations using the broken-symmetry approach and the VWN+B-LYP combination of density functionals, the halide-terminated complexes have a V-V bond order of approximately 2, while complexes featuring OH(-), SH(-), or NH(2)(-) as terminal ligands exhibit full triple bonding between the vanadium atoms. The tendency toward triple bonding in the latter complexes is consistent with an increased covalency of the vanadium-ligand bonds, and the influence of bond covalency is apparent also in the tendency for V-V bond elongation in the complexes with OH(-) and NH(2)(-) terminal ligands. Detailed examination of the composition of molecular orbitals in all of the thioether-bridged V(II) complexes substantiates the conclusion that the strong antiferromagnetic coupling which we have determined for these complexes (-J > 250 cm(-)(1)) is due to direct bonding between metal atoms rather than superexchange through the bridging ligands. As such, these V(II) complexes comprise the first apparent examples of multiple metal-metal bonding in first-transition-row, face-shared dinuclear complexes and are therefore of considerable structural and synthetic interest.

Factors affecting metal-metal bonding in the face-shared d(3)d(3) bioctahedral dimer systems, MM'Cl(9)(5-) (M, M' = V, Nb, Ta)

Density functional theory (DFT) calculations have been used to investigate the d(3)d(3) bioctahedral complexes, MM'Cl(9)(5-), of the vanadium triad. Broken-symmetry calculations upon these species indicate that the V-containing complexes have optimized metal-metal separations of 3.4-3.5 A, corresponding to essentially localized magnetic electrons. The metal-metal separations in these weakly coupled dimers are elongated as a consequence of Coulombic repulsion, which profoundly influences (and destabilizes) the gas-phase structures for such dimers; nevertheless, the intermetallic interactions in the V-containing dimers involve significantly greater metal-metal bonding character than in the analogous Cr-containing dimers. These observations all show good agreement with existing experimental (solid state) results for the chloride-bridged, face-shared dimers V(2)Cl(9)(5-) and V(2)Cl(3)(thf)(6)(+). In contrast to the V-containing dimers, complexes featuring only Nb and Ta have much shorter intermetallic distances (approximately 2.4 A) consistent with d-electron delocalization and formal metal-metal triple bond formation; again, good agreement is found with available experimental data. Calculations on the complexes V(2)(mu-Cl)(3)(dme)(6)(+), Nb(2)(mu-dms)(3)Cl(6)(2-), and Ta(2)(mu-dms)(3)Cl(6)(2-), which are closely related to compounds for which crystallographic structural data exist, have been pursued and provide an insight into the intermetallic interactions in the experimentally characterized complexes. Analysis of the contributions from d-orbital overlap (E(ovlp)) stabilization, as well as spin polarization (exchange) stabilization of localized d electrons (E(spe)), has also been attempted for the MM'Cl(9)(5-) dimers. While E(ovlp) clearly dominates over E(spe) as a stabilizing factor in those dimers containing only Nb and Ta metal atoms, detailed assessment of the competition between E(ovlp) and E(spe) for V-containing dimers is obstructed by the instability of triply bonded V-containing dimers against Coulombic explosion. On the basis of the periodic trends in E(ovlp) versus E(spe), the V-triad dimers have a greater propensity for metal-metal bonding than do their Cr-triad or Mn-triad counterparts.