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.