The chemistry of tervalent uranium

The only previously known compounds of tervalent uranium were prepared in the dry way because of their rapid oxidation by air or water, and the preparation of hydrated salts has been thought impossible. This work reports the preparations, and magnetic and spectral properties of the following, mainly hydrated compounds of tervalent uranium: (a) uranium(Ill) sulphate octahydrate and dihydrate: and the related sparingly soluble double sulphates M[2]SO[4].U[2](SO[4])[3].xH[2]O (M = Na, K, Rb2 Cs, NH[4], and N[2]H[5]), K[5]U(SO[4])[4]. 'H[2]O'; (b) the 'purple' double chlorides MUC1[4].4-5H[2]O (M = K, kb, and NH[4]), and the 'green' double chlorides MUCl[4].ca.6H[2]O (M = Rb and NH[4]); and (c) the first- uranium(III), complexes wish organic ligands, hexakis(phenazone)- and hexakis-(li-aminophenazone) uranium(lII) chloride. These compounds were isolated from aqueous uranium(lll) solutions obtained by electrolytic reduction. All preparations have been carried out under nitrogen to prevent aerial oxidation. Oxidation by water has been minimised by isolating the compounds as rapidly as possible, and by the use of cold solutions and carefully purified reagents. Uranium(IIl) salts such as the sulphates and one series of chlorides are olive-green where water alone is coordinated. These compounds have very similar reflectance and solution spectra. The purple colour of the other series of chlorides which is mainly due to a broad intense hand at 18s000cm.[-1] absent in the other salts, is thought to he due to the effect of coordinated chloride on the f - d transitions. Infra-red spectroscopy has shown the presence of coordinated (bidentate) sulphate in K[5]U(SO[4])[4]. 'H[2]O', hut that the simple sulphates and the other double sulphates contain only ionic sulphate, 'Purple' RhUCl[4]. 4-5H[2]O has far infra-red absorptions at 230cm.[-1] and 196cm.[-1] considered to he due to U - Cl stretching vibrations. The uranium(IIl) sulphates, double sulphates and double chlorides show similar magnetic behaviour. Their moments at room temperature are appreciably lower than the free uranium(lll) ion value, and they decrease with temperature. These compounds obey the Curie-Weiss law but with large theta values and below about 120°K the plots curve towards the temperature axis. The curvature and large theta values are thought to arise from ligand field effects rather than from intermolecular antiferromagnetism.