Preparation and crystal structure of the actinoid ruthenium phosphides ThRu 2P 2 and URu 2P 2

Abstract

The new compounds ThRu 2P 2 and URu 2P 2 were prepared by the reaction between the powders of elemental thorium with RuP and a uranium-ruthenium alloy with elemental phosphorus, respectively, in a tin flux. The compounds crystallize in the orthorhombic space group Pnma with the lattice constants a = 753.15(5) pm [737.9(2) pm], b = 413.95(4) pm [406.7(1) pm], c = 1047.8(1) pm [1029.4(4) pm] for ThRu 2P 2 [URu 2P 2] and Z = 4. The crystal structure was determined from single-crystal X-ray data; R = 0.049 (352 structure factors, 26 variable parameters), R = 0.016 (1109 F values, 27 variables) for the thorium and uranium compound respectively. One phosphorus position of URu 2P 2-χ was found not to be fully occupied: χ = 0.106(5). The structures of ThRu 2P 2 and URu 2P 2 are discussed together with several others of related compositions, for example, BaZn 2As 2 and BaCu 2S 2. While the bonding within the polyanions [Zn 2As 2] 2− and [Cu 2S 2] 2− may be rationalized on the basis of classical two-electron bonds, the structures of ThRu 2P 2 and URu 2P 2 show a tendency for higher coordination as it is typical for intermetallic phases.