Crystal structure and properties of some filled and unfilled skutterudites: GdFe4P12, SmFe4P12, NdFe4As12, Eu0.54Co4Sb12, Fe0.5Ni0.5P3, CoP3, and NiP3

The new cubic compound Fe0.5Ni0.5P3 (a = 775.29(5) pm) as well as the known compounds CoP3 and NiP3 were synthesized from the elemental components usi ng tin as a flux. Their skutterudite (CoAs3) type structures were refined f rom single-crystal X-ray data. The new compound GdFe4P12, was prepared by r eaction of an alloy Gd1/3Fe2/3 with phosphorus in a tin flux. Its cubic "fi lled'' skutterudite (LaFe4P12 type) structure was refined from single-cryst al X-ray data: a = 779.49(4) pm, R = 0.019 for 304 structure factors and 11 variable parameters. SmFe4P12 shows Van Vleck paramagnetism while GdFe4P12 is a soft ferromagnet with a Curie temperature of T-C = 22(5) K. Both are metallic conductors. The new isotypic polyarsenide NdFe4As12 (a = 830.9(1) pm) was obtained by reacting NdAs2 with iron and arsenic in the presence of a NaCl/KCl flux. The new isotypic polyantimonide Eu-0.54(1)Co4Sb12 (a = 90 9.41(5) pm) was prepared by reaction of EuSb2 with cobalt and antimony. Its structure was refined from single-crystal X-ray data to a residual of 0.02 4 (137 F values, 12 variables). A comparison of the Fe-P and P-P bond lengt hs in the compounds AFe(4)P(12), where the A atoms (A = Ce, Eu, Gd, Th) hav e differing valencies, suggests that the Fermi level cuts through Fe-P bond ing and P-P antibonding bands.