Synthesis, characterization, DFT calculations and bromoperoxidase activity of binuclear oxidovanadium complexes containing vitamin B6

Abstract

Two binucelar oxidovanadium complexes, [(VO₂)₂(µ-Hpydn)₂] (1) and [(VO)₂(µ-pydn)₂(bpy)₂]·5H₂O (2), where pydn = pyridoxine and bpy = 2,2’-bipyridine, were synthesized and characterized by elemental analysis and infrared (IR), electron paramagnetic resonance (EPR), and electronic (UV-vis) spectroscopies. The structure of 2 was determined by single-crystal X-ray diffraction analysis. It is comprised of two distorted octahedral oxidovanadium(IV) centers with a terminal bpy ligand and bridged by the methoxido group of the pydn ligands, forming the {V^IVO(µ-OR)₂}²⁺ core with anti-orthogonal configuration. Density functional theory (DFT) calculations at the B3LYP/LANL2DZ level were used to obtain the optimized geometries and to study the electronic structure of 1 and 2. For 2, EPR analysis in the solid state, magnetic susceptibility measurements and the theoretical magnetic exchange coupling constant (J) of 20.1 cm⁻¹ indicate a weak ferromagnetic coupling. ⁵¹V NMR and EPR spectroscopies suggest partial breakage of both binuclear structures in solution. Both complexes act as pre-catalysts for the bromination of phenol red to phenol blue in the presence of KBr, H₂O₂ and perchloric acid.

Graphical Abstract

Keywords:

• Oxidovanadium(IV) and (V)
• vitamin B6
• single-crystal x-ray diffraction
• DFT calculations
• catalytic bromination

Supplementary information

The supplementary material associated with this article can be found in the online version. Crystallographic data for both products have been deposited as CIF files at the Cambridge Crystallographic Data Center with deposition numbers 2129316 for 1 and 2129317 for 2. The files can be obtained free at http://www.ccdc.cam.ac.uk/structures.

Acknowledgements

Authors thank LAMAQ/UTFPR for the ICP-OES analyses. E. L. S. is grateful to the Laboratório Central de Processamento de Alto Desempenho (LCPAD/UFPR) for providing access to computational infrastructure. Authors gratefully thank Dr Jaisa Fernandes Soares and Dr Ronny Rocha Ribeiro for discussions and helpful suggestions. J.M.M., R.C.R.B., G.B.B., F.S.S., D.S., E.L.S and G.G.N. thank CNPq, CAPES-PrInt (Finance Code 001) and pesquisa/PRPPG/UFPR for research grants and scholarships.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was financially supported by Fundação Araucária (project number 20171010), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq-Processes: 406946/2021-3 and 309691/2021-4) and Universidade Federal do Paraná (UFPR) pesquisa/PRPPG/UFPR Edital 04/2020 and Edital 06/2021.