Conformation of six-membered vanadium chelate rings

Vanadium complexes have many desirable catalytic and biological properties across a wide variety of chelate types with coordination moieties typically being oxygen and nitrogen. In this work, we carried out a data mining analysis investigating the conformation of six-membered rings formed between a ligand and a vanadium atom with the objective to understand how much the ligand conformation impacted the structure and stability of the coordination complex. There are 104 structures with the NVN unit in the Cambridge Crystallographic Data Centre (CCDC), 28 structures with OVN unit, 386 structures with the OVO unit, and 11 structures with NVN(sp²)C(sp²) unit, with the remainder of the six-membered ring being three C atoms. The structures containing NVN, OVN, OVO, and NVN(sp²)C(sp²) units show chelate geometries including chair, twist-boat, boat, and half-chair. Out of the total 529 structures, there were 315 chairs (60 %), 91 twist-boats (17 %), 86 boats (16 %), 4 half-chairs (1 %), 2 planar (0.5 %), 13 complexes that contained more than one 6-membered ring and the complex having more than one chelate conformation (2.5 %), and 16 complexes where the structures are not deposited in the CCDC (3 %). Based on the analysis, there is a distinct correlation between the conformation of the ring and the composition of the chelate of the mononuclear, dinuclear and polyoxidovanadate complexes containing NVN, OVN, OVO and NVN(sp²)C(sp²) groups. Therefore, it appears that the chelate composition impacts the conformation of the six-membered ring and thus the stability of the complex.