Intramolecular electron transfer in (BzImH)[(LOV)(2)O] (H2L = S-methyl 3-((2-hydroxyphenyl)methyl)dithiocarbazate): A novel mu-oxo dinuclear oxovanadium(IV/V) compound with a trapped-valence (V2O3)(3+) core

The mononuclear oxovanadium complexes [(VOL)-O-V(OR)] (R: Me, 1a; Et, 1b; Pr-i, 1c) and [(VOLB)-O-IV] (B: Im, 2a; BzIm, 2b) of the tridentate ONS donor ligand S-methyl 3-((2-hydroxyphenyl)methyl)dithiocarbazate (H2L) are reported. The novel mixed-valence (mu-oxo)divanadium(IV,V) complex (BzImH)[(LVO)(2)O] (3) was synthesized using la and 2b as precursors. All of the complexes were characterized by various physical techniques, including H-1 NMR, EPR, and cyclic voltammetry. The X-ray structures of 1a and 3 were determined. Crystals of 1a are triclinic, of space group P (1) over bar, with a 11.045(1) Angstrom, b = 13.429(4) Angstrom, c = 9.611(1) Angstrom, alpha = 100.00(1)degrees, beta = 114.33(1)degrees, gamma = 81.00(1)degrees, 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) Angstrom, b = 20.594(9) Angstrom, c = 14.679(8) Angstrom, beta = 95.28(6)degrees, and Z = 4. 3 is a bent molecule, with a V-O-V bridge angle of 144.0(6)degrees. It has a trapped-valence structure in the solid state with a rare syn-dioxo-mu-oxo [OV-O-VO](3+) core and reveals a 15-line EPR spectrum (V-51, I = 7/2) in solution (CH3CN) 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) similar to 7.3 X 10(9) s(-1)). 3 also exhibits an intervalence transfer (IT) band in solution with features (lambda(max) 970 nm, epsilon 1670 M-1 cm(-1) in CH3CN) 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 (mu-oxo)divanadium(IV,V) complex that exhibits a trapped-valence structure in the solid state and undergoes valence delocalization in solution.