Supramolecular Architecture in an Oxovanadium(V)-Schiff Base Complex: Synthesis, Ab initio Structure Determination from X-ray Powder Diffraction, DNA Binding and Cleavage Activity

Abstract

The synthesis, spectroscopic characterization, X-ray powder structure determination, and thermal behavior of a binuclear bis(μ-oxo)-bridged vanadium(V) complex, [(VO2L)2], L = N,N‘-dimethylenediamine(o-hydroxyl acetophenon), along with its DNA binding ability and photoinduced DNA cleavage activity, have been described. The compound crystallizes in a monoclinic system with a = 7.679(3) Å, b = 12.020(5) Å, c = 13.882(6) Å, β = 90.799(4)°, space group P21/c, and Z = 2. The crystal structure has been solved from laboratory X-ray powder diffraction data using the direct space approach and refined by the Rietveld method. The dimeric complex consists of two edge-sharing vanadium octahedra with each metal center coordinated to one oxo-, one phenolate-, and two bridging-oxygen ligands, and two nitrogen donor atoms. The molecular structure reveals a two-dimensional grid of (24) rings in the (011) plane, which on combination with one-dimensional polymeric chains along the [100] direction, forms a novel three-dimensional supramolecular framework. Thermogravimetric analysis of the complex indicates multiple overlapping decomposition steps in the temperature range 180−800 °C with the end product being V2O5. The complex binds to double-stranded DNA giving a Kapp value of 1.56 × 107 M-1 and displays DNA cleavage activity on UV (300 nm) irradiation via a mechanistic pathway involving formation of singlet oxygen as the reactive species.