Some six-co-ordinate complexes of uranium(VI)

Abstract

Twenty complexes of uranium(VI), of the type [UO₂A₂B₂]^z(A, B = Cl, Br, I, Ph₃PO, or Et₃PO; the charge z=+ 2, 0, or –2), have been prepared and characterised. The interconversion of these compounds with uranium(VI) compounds is described. Infrared measurements show that (i) the phosphine oxide and chloro-complexes have trans configurations, (ii) the asymmetric stretching frequency of the uranyl group varies irregularly with A and B, and (iii) the symmetric stretch of the uranyl group is active in some cases, probably owing to hydrogen-bonding with (R₃PH)⁺ cations. The paramagnetic susceptibility of the uranyl ion in these complexes (86–147 × 10^–6 e.m.u./g.mol.) is independent of temperature. Finally, it is suggested that the previously reported tertiary phosphine complexes of uranium(IV) and uranium(VI), [UX₄(R₃P)₂] and [UO₂X₂(R₃P)₂](R = Et, Prⁿ, or Ph; X = Cl, Br, or I), are [R₃PH]₂[UO₂X₄] and [UO₂X₂(R₃PO)₂], respectively.