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Mixed-Oxidation Divanadium(IV,V) Compound with Ligand Asymmetry: Electronic and Molecular Structure in Solution and
Subodh Kanti Dutta1, Satyabrata Samanta, Sujit Baran Kumar
1Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Calcutta 700 032, India, Magnetic Resonance Group, Korea Basic Science Institute, Yeueun-dong 52, Yoosung-goo, Taejeon, 305-333, South Korea, and Department of Chemistry, College of Arts and Sciences, The University of Toledo, Toledo, Ohio 43606-3390.
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.