Ep. Copeland et al., NOVEL MIXED-VALENCE VANADIUM(IV V) MOLECULE EXHIBITING UNUSUAL ELECTRON DELOCALIZATION OVER THE [V2O3](3+) CORE/, Journal of the Chemical Society. Dalton transactions, (16), 1997, pp. 2849-2852
Condensation of methanolic salicylaldehyde and triethylenetetramine in
the presence of vanadyl sulfate (VOSO4) in a 3:1:2 mole ratio respect
ively 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 c
entres. The EPR spectra of frozen solutions and polycrystalline sample
s of 1 revealed extensive vanadium-vanadium interactions which are mos
t evident in the 15-line solution EPR spectrum in dimethyl sulfoxide o
r acetonitrile at room temperature. Cyclic voltammograms showed a sing
le electron loss at E-1/2 = 0.486 V (with respect to the standard calo
mel electrode).