Synthesis, structure and properties of three new oxidovanadium complexes containing a tridentate salicylaldehydeglycine

Three new oxidovanadium complexes as potential functional model vanadium-dependent haloperoxidases: [VO2(C9H7NO3)](C10H10N2)0.5 (1), [VO(C10H8N2)(C9H7NO3)]3 (2) and [VO(C12H8N2)(C9H7NO3)]·2.33H2O (3) have been designed and synthesized under room temperature with mixed solution of CH3OH and H2O. All the complexes have been characterized by elemental analysis, IR spectra, UV–vis spectroscopy and X-ray single crystal diffraction. The structural analysis indicates that the three complexes are all containing a tridentate amino-Schiff-base (salicylideneglycinate) with imine nitrogen, phenoxyl, and carboxyl oxygen as three donor atoms. The asymmetric unit of complex 1 is formed by one [VO2(C9H7NO3)]– anion and half of (C10H10N2)2+ cation, in which the nitrogen atoms of 4,4′-bipy were protonated. For complex 1, the coordination environment of the central vanadium atom is almost ideal square pyramid, while for complexes 2 and 3, the vanadium atom is a six-coordinated and in a distorted octahedral environment. It is found that there are a variety of inter- and intra-molecular hydrogen bonds in all the three complexes. What is intriguing to us is that the oxidation state of the central metal atom in complex 1 is different from that of complex 2 and 3: the oxidation state of vanadium in complex 1 is +5, while ones in complex 2 and 3 are +4. Bromination reaction activity of the complexes has been evaluated by the method with phenol red as organic substrate in the presence of H2O2, Br– and phosphate buffer, indicating that they can be considered as potential functional model vanadium-dependent haloperoxidases. In addition, thermal analysis, cyclic voltammetry and quantum chemistry calculations were also performed and discussed in detail.