The chemistry of quadrivalent lanthanoids

Cerium tetrachloride complexes, viz. [CeCl4L2] and [CeCl4L] where L = a uni-or bi-dentate arsine oxide, a phosphine oxide, a sulphoxide, or an amide, have been prepared. The thermal degradation behaviour of the solids could be divided into three patterns, one of which consists of loss of a chlorine atom only. It was indicated that [CeCl4(ipae)2] could act as a substitute for the thermally unstable CeCl4 for solution studies [ipae = 1-(di-isopropylamino)ethanal]. Decomposition rate studies of solutions of [CeCl4(ipae)2] and Cs2[CeCl6] in different solvents indicated that the decomposition reaction is first order with respect to cerium(IV) and its rate is approximately proportional to the donor number of the solvent. Solutions in thionyl chloride are stable for an indefinite period. The compounds studied were compared with their uranium(IV) analogues with respect to co-ordination behaviour, i.r. spectra, non-aqueous conductometric behaviour, and solvoscopic nature. The CeCl4 and UCl4 complexes proved very similar in almost all respects, except that those of cerium(IV) were more solvoscopic. Some differences between cerium(IV) and uranium(IV) can probably be explained best in terms of differences between 4f and 5f metal character rather than size differences. (author)