DISCRETE VARIATIONAL X-ALPHA STUDIES OF THE ELECTRONIC-STRUCTURE OF AMAVADIN

Discrete variational X alpha (DVX(alpha)) calculations have been carri ed out for the eight-co-ordinated vanadium (IV) and -(V) complexes [V( hida)(2)](2-/1-) (H(3)hida = N-hydroxyiminodiacetic acid). These compl exes are minimal models for the corresponding oxidation states of amav adin from Amanita muscaria which, as isolated, consists of an approxim ately equimolar mixture of the anions [Delta-V [{(S,S) hidpa}(2)](2-) and [Lambda-V {(S,S)-hidpa}(2)](2-) (H(3)hidpa = N-hydroxy-2,2'-iminod ipropionic acid). The electronic structure and the nature of the metal - ligand bonding of these vanadium-(IV) and -(V) centres is described. The ordering of the d orbitals and their composition is closely relat ed to that established for the oxovanadium(IV) moiety which demonstrat es why, for many years, amavadin was mistakenly thought to contain a V O2+ centre.