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.

The mononuclear oxovanadium complexes [V V OL(OR)] (R: Me, 1a; Et, 1b; Pr i , 1c) and [V IV OLB] (B: Im, 2a; BzIm, 2b) of the tridentate ONS donor ligand S-methyl 3-((2-hydroxyphenyl)methyl)dithiocarbazate (H 2 L) are reported. The novel mixed-valence (µ-oxo)divanadium(IV,V) complex (BzImH)[(LVO) 2 O] (3) was synthesized using 1a and 2b as precursors. All of the complexes were characterized by various physical techniques, including 1 H NMR, EPR, and cyclic voltammetry. The X-ray structures of 1a and 3 were determined. Crystals of 1a are triclinic, of space group P1 h, with a ) 11.045(1) Å, b ) 13.429(4) Å, c ) 9.611(1) Å, R ) 100.00(1)°, β ) 114.33(1)°, γ ) 81.00(1)°, and Z ) 4. The asymmetric unit of 1a contains two independent molecules with minor conformational differences. Crystals of 3 are monoclinic, of space group P2 1 /n, with a ) 10.10(1) Å, b ) 20.594(9) Å, c ) 14.679(8) Å, β ) 95.28(6)°, and Z ) 4. 3 is a bent molecule, with a V-O-V bridge angle of 144.0(6)°. It has a trapped-valence structure in the solid state with a rare syn-dioxo-µ-oxo [OV-O-VO] 3+ core and reveals a 15-line EPR spectrum ( 51 V, I ) 7 / 2 ) in solution (CH 3 CN) at room temperature, indicating delocalization of the odd electron. The spectrum gradually changes its profile with the lowering of temperature and ultimately collapses into an 8-line pattern at 225 K due to thermal trapping of the odd electron (k th ∼ 7.3 × 10 9 s -1 ). 3 also exhibits an intervalence transfer (IT) band in solution with features (λ max 970 nm, 1670 M -1 cm -1 in CH 3 CN) remaining practically unaffected by the change of solvents. The IT band was analyzed by Gaussian curve fitting, and the electron exchange integral H AB was estimated as 2210 cm -1 . Thus, 3 appears to be an interesting mixed-oxidation-state (µ-oxo)divanadium(IV,V) complex that exhibits a trapped-valence structure in the solid state and undergoes valence delocalization in solution.