Mixed-Oxidation Divanadium(IV,V) Compound with Ligand Asymmetry: Electronic and Molecular Structure in Solution and in the Solid State.

Abstract

Reaction of [V(IV)OL(1)(Im)] (H(2)L(1) = S-methyl-3-((2-hydroxyphenyl)methyl)dithiocarbazate) with [V(V)OL(OCH(3))] allows isolation of (ImH)[L(1)OV-(&mgr;-O)-VOL] complexes 2 (H(2)L = H(2)L(2) = S-methyl-3-((5-bromo-2-hydroxyphenyl)methyl)dithiocarbazate) and 3 (H(2)L = H(2)L(1)), one of which (2) has ligand asymmetry not previously known in this type of complex. In the solid state, (ImH)[L(1)OV-(&mgr;-O)-VOL(2)] (2) provides an example of a divanadium(IV,V) compound with a syn angular [V(2)O(3)](3+) core structure that exhibits crystallographically imposed mirror symmetry due to static disorder. Crystals of 2 are orthorhombic, space group Pnma, with a = 10.740(2) Å, b = 18.912(4) Å, c = 17.163(4) Å, and Z = 4. In toluene at room temperature, both 2 and 3 have 8-line EPR spectra, characteristic of trapped-valence structure. When acetonitrile is added to these solutions, the spectra reveal 15-line features with asymmetric distortions that smooth out with the lowering of temperature. This probably has its origin in a solvent-dependent equilibrium involving two magnetically inequivalent structural forms of the divanadium(IV,V) compound, with syn angular and anti linear structures of the [V(2)O(3)](3+) core. Variable temperatures (298-220 K) (51)V NMR spectroscopic studies in solution also support this view. In acetonitrile, both 2 and 3 exhibit an intervalence transfer band in the near-IR region at ca. 970 nm (epsilon, 1600 and 1480 M(-)(1) cm(-)(1) for 2 and 3, respectively) and they undergo one-electron reversible oxidation at ca. 0.40 V (vs SCE) due to the V(IV)V(V)/V(V)V(V) couple.