Formation in aqueous solution of a non-oxido VIV complex with VN6 coordination. Potentiometric, ESI-MS, spectroscopic and computational characterization

Abstract

The behaviour of the system formed by V(IV)O(2+) ion with all-cis-2,4,6-trimethoxycyclohexane-1,3,5-triamine (tmca) was characterized in aqueous solution through the combined application of electron paramagnetic resonance (EPR) and UV-Vis spectroscopy, electrospray ionization mass spectrometry (ESI-MS), pH-potentiometry and DFT methods. The formation of an unusual non-oxido [V(tmcaH-2)2] species with VN6 coordination, with the ligand in the bianionic form, was demonstrated. The geometry, EPR and UV-Vis spectra and electronic structure of [V(tmcaH-2)2] were simulated with Gaussian 09 and ORCA software and the results were compared with those of similar oxido and non-oxido vanadium(iv) species formed by other polyamine and polyol related ligands, such as 1,3,5-triamino-1,3,5-trideoxy-cis-inositol (taci), 1,3,5-trideoxy-1,3,5-tris(dimethylamino)-cis-inositol (tdci), cis-inositol (ino) and 1,3,5-trideoxy-1,3,5-trimethoxy-cis-inositol (tmci). The results indicate that V(IV)O(2+) species are formed in acid and weakly basic solution and that [V(tmcaH-2)2] is observed above pH 10. In the non-oxido complex, DFT calculations suggest that the two -NH2 groups are in trans position and that the pre-organization of the ligands favours the metal complexation and the formation of the hexa-coordinated species with VN6 coordination.

Structural and redox requirements for the action of anti-diabetic vanadium compounds

“…19 The transformation of a V IV into a V IV O species can be followed by EPR spectroscopy. In particular, a significant increase of the highest value of the 51 V anisotropic hyperfine coupling constant, from 95-145 to 155-165 × 10 −4 cm −1 , is observed, in agreement with what is reported in the literature; 38 the results are confirmed by DFT calculations of the 51 V A values (Table 2). We conclude that three of the six V IV complexes convert to…”

Coordinative interaction of microcrystalline chitosan with oxovanadium (IV) ions in aqueous solution

“…The parts of curves after a  ~ 1 (end point of MCCh), the longer the higher is the part of vanadyl ion, are evidently connected with VO(IV) – MCCh complexation via the deprotonated hydroxyl groups but not the amine groups. This result is not surprising because it is known that the affinity of V IV O 2+ ion is much higher towards ligands with oxygen donors [27-29]. Coordinative interaction of oxido V IV O 2+ ion towards only nitrogen donors is very low and results in hydrolytic processes in acid and neutral solution.…”

VIVO and VIV Species Formed in Aqueous Solution by the Tridentate Glutaroimide–Dioxime Ligand – An Instrumental and Computational Characterization

“…Nowadays, the prediction of 51 V HFC tensor A is possible through the DFT methods. We recently observed that the ORCA software gives better results than popular Gaussian for non‐oxido vanadium(IV) complexes, because it includes the second‐order spin–orbit effects, whose contribution to A is more important than for V IV O species , , . Among the functionals, it has been recently demonstrated that, for a bare V IV complex, the double hybrid B2PLYP gives a mean percentage deviation (MPD) from A iso of –0.3 % if using the basis set VTZ, and from A i ( i = x or z , depending on the symmetry and electronic structure of the complex) of –0.9 % if using the 6‐311g(d,p) basis set .…”