The chemistry of the trivalent actinides. Part II. Uranium(III) double chlorides and some complexes with oxygen-donor ligands

Abstract

Two series of hydrated double chlorides have been isolated and characterised. Compounds of the red series, M^IUCl₄,5H₂O (M^I= K, Rb, or NH₄), have an intense absorption at 18,000 cm^–1 in their reflectance spectra and in the spectra of their solutions in methanol and 11M hydrochloric acid. There are also bands at 230 and 196 cm^–1 in the spectrum of RbUCl₄,5H₂O which can be assigned to U–Cl stretching vibrations. These electronic and far i.r. bands are absent from the spectra of the green series, M^IUCl₄xH₂O (M^I= Rb or NH₄), as these closely resemble the reflectance spectra of the uranium(III) sulphates and double sulphates and the spectrum of the hydrated uranium(III) ion. In water the red series gave the spectrum of the hydrated uranium(III) ion. Thus the red series is believed to contain co-ordinated chloride while the green compounds contain uranium(III) in a more ionic environment. Owing to the presence of a small amount of M^ICl, the degree of hydration of the green series is uncertain. Corresponding bromides could not be isolated. Like the lanthanide(III) metal ions, uranium(III) forms complexes; [U(phaz)₆]Cl₃ or (Ph₄B)₃, and [U(dmaz)₄](Ph₄B)₃, with the oxygen-donor ligands phenazone (phaz,1-phenyl-2,3-dimethyl-5-pyrazolone) and 4-dimethylaminophenazone (dmaz), which were isolated from alcoholic solutions of the red double chlorides and the ligands. These complexes are readily oxidised by air and water, and this reactivity prevents an extensive study of the complexing ability of trivalent uranium; many other oxygen-donor ligands were investigated but oxidation of the uranium(III) occurred even under nitrogen.