Adduct formation between bis(β-diketonato) oxovanadium(IV) complexes and 4-methylpyridine N-oxide

Characterization of the Potent Insulin Mimetic Agent Bis(maltolato)oxovanadium(IV) (BMOV) in Solution by EPR Spectroscopy

“…Electron spin echo envelope modulation studies should be able to provide a definitive answer to the origin of the line broadening and hence the structure of this complex. Given existing results in the literature, − we conclude pyridine coordinates cis to the oxo group.…”

“…Depending on the coordinating ability of a solvent, complexation of the coordinatively unsaturated VO(ma) 2 species cis F1 and trans F2 (Chart ) with solvent molecules may take place in solution. Precedence for such solvation can be found in EPR, − IR, − and X-ray crystallographic 38,39 studies on related oxovanadium(IV) chelate compounds. Chart depicts all possible solvated VO(ma) 2 complexes, where S represents a solvent molecule.…”

“…A cis configuration for the pyridine adduct VO(ma) 2 (py) is concluded on the basis of two pieces of evidence. IR, EPR, and ENDOR spectroscopic results suggest that most pyridine and substituted pyridine adducts of bis(β-diketonato)oxovanadium(IV) either are only cis or are a mixture of cis and trans isomers in solution. − Pyridine is known to coordinate strongly to transition metal ions, and other strong (anionic) ligands such as OR - and O 2- are always found cis in bis(maltolato)oxovanadium(V) complexes. , The frozen solution anisotropic EPR spectrum (Figure S1a) of VO(ma) 2 in CH 2 Cl 2 /pyridine revealed the presence of a single species. (Note: Figures S1−S6 are supplied as Supporting Information.)…”

“…22 Depending on the coordinating ability of a solvent, complexation of the coordinatively unsaturated VO(ma) 2 species cis F1 and trans F2 (Chart 1) with solvent molecules may take place in solution. Precedence for such solvation can be found in EPR, [32][33][34] IR, [35][36][37] and X-ray crystallographic 38,39 all possible solvated VO(ma) 2 complexes, where S represents a solvent molecule. When S is incorporated at a sixth coordination position in VO(ma) 2 , its coordination site may be either cis (C) or trans (T) to the unique oxo ligand (referred to as the cis or trans isomer).…”

“…Solvation effects in bis(β-diketonato)oxovanadium(IV) complexes (VO(acac) 2 in particular, acac being acetylacetonate) have been extensively studied by EPR, , electron nuclear double resonance (ENDOR), and infrared (IR) − spectroscopies, as well as by X-ray crystallography. , There is much to be learned from this literature despite the fact that β-diketonates are bidentate ligands which form six-membered metallacycle complexes with metal ions, whereas the analogous maltol derivatives are five-membered metallacycles. The different ring sizes may cause variations in properties such as stability and solvation.…”