SYNTHESIS AND STRUCTURES OF NIOBIUM(V) AND TANTALUM(V) ANALOGS OF AMAVADIN - [M(HIDA)(2)](-) (M=NB-V OR TA-V, H(3)HIDA EQUALS HYDROXYIMINO-DIACETIC ACID) AND [NB(R,R-HIDPA)(2)](-) [H(3)HIDPA=2,2'-(HYDROXYIMINO)-DIPROPIONIC ACID]

Reactions of M(OEt)(5) (M = Nb or Ta) with N-hydroxyiminodiacetic acid (H(3)hida) yielded the complexes [M(hida)(2)](-) (M = Nb 1 or Ta 2). Single-crystal X-ray diffraction revealed the Same novel eight-co-ordi nated structure identified for Amavadin, the form is which vanadium(Iv ) is bound in Amanita muscaria mushrooms. 1 This type of structure giv es rise to chirality at the metal, where 1 and 2 consist of an equimol ar mixture of the Delta and Lambda helical forms in the crystal lattic e. The complexes [Nb(R,R-hidpa)(2)](-) 3a and [Nb(R,S-hidpa)(2)](-) 3b [H(3)hidpa = 2,2'-(hydroxyimino)dipropionic acid] were synthesized vi a the route used for 1 and 2, and X-ray crystallography confirmed the presence of the same Amavadin-style geometry. Cyclic voltammetry-in CH 2Cl2 showed that at 254 K 1 and 3a exhibit quasi-reversible reductions at E(1/2) = -1.22 and -1.35 V (vs. saturated calomel electrode), resp ectively, whereas 2 displays an irreversible reduction (-1.92 V).