U₃TiSb₅, U₃VSb₅, U₃CrSb₅, and U₃MnSb₅ with "Anti"-Hf₅Sn₃Cu Type Structure

Abstract

The title compounds have been prepared from the elemental components by arc-melting and subsequent annealing. Single crystals of U 3 TiSb 5 and U 3 MnSb 5 were obtained from a tin flux and their structures were determined from single-crystal X-ray data: P6 3 /mcm, Z = 2; a = 913.9(2), c = 611.2(1) pm, R = 0.011 (233 structure factors, 14 variables) for U 3 TiSb 5 and a = 916.8(2), c = 613.2(1) pm, R = 0.015 (427 structure factors, 14 variables) for U 3 MnSb 5 . The lattice constants of the isotypic compounds are: a = 908.2(2), c = 608.3(2) pm for U 3 VSb 5 and a = 911.0(1), c = 611.5(1) pm for U 3 CrSb 5 . The structure of these antimonides may be regarded as an “anti”-type structure of Hf 5 Sn 3 Cu with the antimony atoms on the hafnium sites, while the positions of the uranium and transition metal atoms correspond to the positions of the tin and copper atoms. A comparison of the interatomic distances of U 3 TiSb 5 with those of U 3 Sb 4 , USb 2 , and a-antimony suggests oxidation numbers according to (U +III ) 3 Ti +IV (Sb1 -III ) 3 (Sb2 -II ) 2 , where the Sb2 atoms form weakly bonded chains