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Issue 11, 2017
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Coordination of o-benzosemiquinonate, o-iminobenzosemiquinonate and aldimine anion radicals to oxidovanadium(IV)

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Abstract

The study focuses on the stabilization of organic radicals by the oxidovanadium(IV) ion and it proves to be significant in exploring the bioactivity of vanadium. In addition to the o-benzosemiquinonate and o-iminobenzosemiquinonate anion radicals, the existence of reactive aldimine anion radicals coordinated to oxidovanadium(IV) ion was detected. Radical and non-radical oxidovanadium(IV) complexes of the types [(L1)(VIVO)(acac)] (1), [(L2)(VIVO)(acac)] (2), [(L1)(VIVO)(sq˙)] (3), [(L1)(VIVO)(t-Busq˙)] (4), [(L1)(VIVO)(NO2isq˙)] (5) and [(L1)2(VIVO)2(SO4)]·½CH2Cl2 (6·½CH2Cl2) containing redox non-innocent tridentate NNO-donor aldimines (L1H and L2H) as coligands are reported (acac = acetylacetonato, sq˙ = o-benzosemiquinonate, t-Busq˙ = 3,5-di-tert-butyl-o-benzosemiquinonate and NO2isq˙ = p-nitro-o-iminobenzosemiquinonate anion radicals). The sq˙, t-Busq˙ and NO2isq˙ states in complexes were established by X-ray crystallography, EPR spectroscopy and solid state cross polarization magic angle spinning (CP/MAS) 51V NMR spectroscopy, where the 51V nuclei in 3–5 were deshielded in a range from −100.3 to +608.7 ppm. The cathodic waves of 1 and 2 due to L1/L1˙2− and L2/L2˙2− redox couples are reversible. Density functional theory (DFT) calculations authenticated that 1 and 2 are open shell pi radical (L1˙2− and L2˙2−) complexes of oxidovanadium(IV). The energies of the open shell singlet (OSS) and triplet solutions of 1 and 2 are lower than the corresponding closed shell singlet (CSS) solutions. In 1 and 2 ions, 35–39% beta spin is localized on the πaldimine* function. The UV-vis-NIR absorption spectra of the complexes were analyzed by spectroelectrochemical measurements and time dependent (TD) DFT calculations.

Graphical abstract: Coordination of o-benzosemiquinonate, o-iminobenzosemiquinonate and aldimine anion radicals to oxidovanadium(iv)

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Publication details

The article was received on 16 Jan 2017, accepted on 26 Apr 2017 and first published on 26 Apr 2017


Article type: Paper
DOI: 10.1039/C7NJ00186J
Citation: New J. Chem., 2017,41, 4564-4572
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    Coordination of o-benzosemiquinonate, o-iminobenzosemiquinonate and aldimine anion radicals to oxidovanadium(IV)

    M. Shit, S. Bera, S. Maity, T. Weyhermüller and P. Ghosh, New J. Chem., 2017, 41, 4564
    DOI: 10.1039/C7NJ00186J

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