Novel mixed-valence vanadium(IV/V) molecule exhibiting unusual electron delocalization over the [V2O3](3+) core

Condensation of methanolic salicylaldehyde and triethylenetetramine in the presence of vanadyl sulfate (VOSO4) in a 3:1:2 mole ratio respectively yielded a new dinuclear mixed-valence vanadium(IV/V) Schiff-base molecule [V2O3L1] 1. The crystal structure of 1 revealed the molecule to be in a bent conformation with the vanadyl units (VO) cis to each other and to the oxo VOV bridge. The V(mu-O)(mu-phenolate)V bridge is marginally asymmetric [V-O(oxo)1.811(2) and 1.841(2), V-O-phenolate 2.180(2) and 2.203(2) Angstrom]. Normally, these geometrical properties are considered unfavourable for electron delocalization over the oxo V-O-V bridge. However, remarkably, the paramagnetic molecule 1 (mu = 1.73 mu(B)) features an unpaired electron delocalized over the vanadyl centres. The EPR spectra of frozen solutions and polycrystalline samples of 1 revealed extensive vanadium-vanadium interactions which are most evident in the 15-line solution EPR spectrum in dimethyl sulfoxide or acetonitrile at room temperature. Cyclic voltammograms showed a single electron loss at E-1/2 = 0.486 V (with respect to the standard calomel electrode).