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Issue 23, 1997
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New vanadium-(IV) and -(V) analogues of Amavadin

Abstract

The new pro-ligand meso-2,2′-(hydroxyimino)dibutyric acid (R,S-H3hidba) has been synthesised from hydroxylammonium chloride and 2-bromobutyric acid. Reaction of H3hidba with [VO(acac)2] (acac = acetylacetonate) yielded the complex [V(R,S-hidba)2]2– 1, which was crystallised in the presence of Ca2+ ions from H2O as blue tabular crystals. X-Ray crystallography confirmed the same distinctive eight-co-ordinate structure of the complex anion as identified for Amavadin, the form in which vanadium(IV) is bound in Amanita muscaria mushrooms. The crystal structure of 1 contains a network of linked Ca and V centres where the asymmetric unit consists of a Ca2V2 box-like configuration. The Ca and V metal ions are bridged to one another via a series of unidentate and bidentate carboxylate groups from H3hidba, extending throughout the lattice framework. The novel interaction between Ca2+ ions and Amavadin-style complexes has been further illustrated in the crystal structure of [Ca(H2O)5][V(hida)2]·H2O (H3hida = N-hydroxyiminodiacetic acid) 2. The unit cell packing arrangement observed for 2 differs from 1, comprising helical chains formed by alternate Ca and V units linked only by unidentate carboxylate groups. Cyclic voltammetric studies of 1 exhibited a reversible VV–VIV redox couple in H2O (E½ = +0.43 V, vs. saturated calomel electrode), this oxidation potential is considerably lower in organic solvents (e.g. Me2SO, E½ = –0.07 V). The chemical oxidation of 1 in aqueous medium by ammonium ceric nitrate produced a dark red solution which was transferred into CH2Cl2 using [PPh4]Br. From this solution [PPh4][V(R,S-hidba)2] 3 was isolated and studied using 1H, 13C and 51V NMR spectroscopy. The cyclic voltammogram of 3 also displays a reversible VV–VIV redox couple in CH2Cl2 (E½ = –0.09 V).

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Article type: Paper
DOI: 10.1039/A703683C
J. Chem. Soc., Dalton Trans., 1997, 4509-4516

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    New vanadium-(IV) and -(V) analogues of Amavadin

    P. D. Smith, R. E. Berry, S. M. Harben, R. L. Beddoes, M. Helliwell, D. Collison and C. David Garner, J. Chem. Soc., Dalton Trans., 1997, 4509
    DOI: 10.1039/A703683C

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