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

Abstract

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 [VO₂L¹]1 and [VO₂L²]2(L¹ and L² 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′= 0.139) 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 ⁵¹V NMR spectroscopy. These species are convertible back to the dioxovanadium(V) complexes upon addition of water to the photoirradiated solution.