Structure, characterization and photoreactivity of monomeric dioxovanadium(V) Schiff-base complexes of trigonal-bipyramidal geometry

Five mononuclear cis-dioxovanadium(v) complexes of tridentate Schiff bases derived from salicylaldehyde and its derivatives and 8-aminoquinoline have been synthesized and characterized. Single-crystal X-ray analyses were performed with [VO(2)L(1)] 1 and [VO(2)L(2)] 2 (L(1) and L(2) denote the [1 + 1] Schiff-base anions derived from salicylaldehyde or naphthaldehyde and 8-aminoquinoline). While the structure of 2 was refined to a final R = 0.074(R' = 0.055), that of 1 was refined only to R = 0.134(R' = 0.134) due to its poor diffraction quality. The complexes contain cis-oxo groups in the equatorial plane and a trigonal-bipyramidal geometry around the vanadium at which the Schiff base binds meridionally. Photoirradiation of these complexes in CH2Cl2 yielded chloride-bound VO3+ species, as studied using absorption and V-51 NMR spectroscopy. These species are convertible back to the dioxovanadium(v) complexes upon addition of water to the photoirradiated solution.