Intramolecular electron transfer in (BzImH)[(LOV)20](H2L = S-methyl 3-((2-hydroxyphenyl)methyl)dithiocarbazate): a novel m-oxo dinuclear oxovanadium(IV/V) compound with a trapped-valence (V2O3)3+ core

Abstract

The mononuclear oxovanadium complexes [VVOL(OR)] (R: Me, 1a; Et, 1b; Pri, 1c) and [VIVOLB] (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 (μ-oxo)divanadium(IV,V) complex (BzImH)[(LVO)2O] (3) was synthesized using 1a and 2b as precursors. All of the complexes were characterized by various physical techniques, including 1H NMR, EPR, and cyclic voltammetry. The X-ray structures of 1a and 3 were determined. Crystals of 1a are triclinic, of space group P, with a = 11.045(1) Å, b = 13.429(4) Å, c = 9.611(1) Å, α = 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 P21/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 (51V, 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 (kth 7.3 × 109 s-1). 3 also exhibits an intervalence transfer (IT) band in solution with features (λmax 970 nm, ε 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 HAB 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.