GENERATION OF THE V(NO)2-) USING HYDROXYLAMINE AND PSEUDO-HALIDE IONS- SYNTHESIS AND ELECTROCHEMISTRY OF [V(NO)2(L-L)2]X (L-L = 2,2'-BIPYRIDINE OR 1,10-PHENANTHROLINE)( MOIETY FROM VO4(3)

Vanadate in aqueous alkali reacted with NH2OH.HCl and X- (X- = NCS-, N 3- or CN-) ions only in the presence of L-L [L-L = 1,10-phenanthroline (phen) or 2,2'-bipyridine (bipy)] ligands and at ca. 35-degrees-C to yield [V(NO)2(L-L)2]X (X = NCS 1, N3 2 or CN 9, L-L = phen; X = NCS 3, N3 4 or CN 10, L-L = bipy). Anion metathesis yields [V(NO)2(phen)2]Y (Y = ClO4 5 or BPh4 6) and [V(NO)2(bipy)2]Y (Y = ClO4 7 or BPh4 8). Th e complexes behave as 1 : 1 electrolytes in methanol, acetonitrile and dimethylformamide and exhibit four-band electronic spectra. The solid s are diamagnetic, compatible with the existence of a {V(NO)2}6 moiety in all the complexes. Since the NO ligands occupy cis positions, the overall symmetry of the molecules is low, which is supported by the H- 1 NMR data of 1 and 3, which show that two L-L ligands are in differen t magnetic environments. All the complexes exhibit two successive L-L centred single-electron reductive cyclic responses at negative potenti als corresponding to E298-degrees of ca. -1.30 and ca. -1.50 V vs. sat urated calomel electrode (SCE), typical for some d6 systems. At positi ve potentials, the phen complexes show one metal-centred oxidative cyc lic response at E298-degrees ca. 0.60 V vs. SCE and two irreversible o xidative responses at higher potentials. The bipy complexes, however, show four consecutive irreversible oxidative peaks. In the case of the phen complex 5, the first oxidative response has been confirmed as me tal centred by EPR data after exhaustive coulometry, which shows a typ ical V-51 hyperfine (octet), as well as superhyperfine splitting (none t) due possibly to the interaction of the unpaired electron with phen nitrogens.