Crystal structure and NMR study of a bisperoxovanadium complex [NH4][VO(O2)2(ima)

Abstract

A novel bisperoxovanadium complex, [NH4][VO(O2)2(ima)] (1) (ima = imidazole-4-carboxamide), was synthesized by the reaction of NH4VO3 and ima in the presence of H2O2, and the structure was characterized by single-crystal X-ray technology. The adjacent [NH4][VO(O2)2(ima)] monomers further constructed a 3-D supramolecular framework through intra- and intermolecular hydrogen bonding interactions. The composition of the title complex solution was explored using a combination of multinuclear (1H, 13C and 51V) magnetic resonance, heteronuclear single quantum coherence (HSQC), and variable temperature NMR in a 0.15 mol L−1 NaCl/D2O solution that mimics physiological conditions. According to NMR experimental results, a pair of isomers (Isomers A and B) are observed in aqueous solution, which are attributed to different types of coordination modes between the metal center and the ligands; Isomer B (the main product) has the same coordination structure as the crystal structure of [NH4][VO(O2)2(ima)]. The 51V NMR experiment together with single-crystal X-ray diffraction results indicated that Isomer A is the hexa-coordinated peroxovanadium species while Isomer B is the hepta-coordinated species.