SCANDIUM IRIDIUM BORIDE SC3IR5B2 AND THE QUATERNARY DERIVATIVES SC2MIR5B2 WITH M = BE, AL, SI, TI, V, CR, MN, FE, CO, NI, CU, GA, OR GE - PREPARATION, CRYSTAL-STRUCTURE, AND PHYSICAL-PROPERTIES

The new compounds Sc3Ir5B2 and Sc2MIr5B2 with M = Be, Al, Si, Ti, V, C r, Mn, Fe, Co, Ni, Cu, Ga, or Ge were prepared by are-melting appropri ate compressed mixtures of the elemental components in an argon atmosp here. They crystallize tetragonally with Z = 2 in the space group P4/m bm with lattice constants a = 952.6(1) pm and c = 304.8(1) pm for Sc3I r5B2 and ranging from a = 927.0(1) pm and c = 296.8(1) pm (Sc2BeIr5B2) to a = 932.9(1) pm and c = 310.3(1) pm (Sc2TiIr5B2) for the quaternar y compounds. According to powder diagrams, all compounds are isotypic. Structure determinations based on single-crystal X-ray data were perf ormed for Sc2SiIr5B2, Sc2VIr5B2, and Sc2FeIr5B2. Sc3Ir5B2 crystallizes with the Ti3Co5B2-type compounds, while the quaternary compounds form an ordered substitutional variant of this structure. The M atoms are arranged in rows along [001] with M-M distances of similar to 300 pm i n the rows and similar to 660 pm between the rows. For the compounds w ith M = Mn, Fe, or Co, this results in highly anisotropic magnetic pro perties. Susceptibility measurements with a Faraday balance in the ran ge 7-770 K suggest ferromagnetic coupling in the rows at low temperatu res. Between the rows, the coupling was antiferromagnetic for Sc2FeIr5 B2 (T-N approximate to 190 K) and ferromagnetic for Sc2MnIr5B2 (T-C ap proximate to 115 K, mu(s) approximate to 1.2 mu(B)) and for Sc2CoIr5B2 (T-C approximate to 135 K, mu(s) approximate to 1.2 mu(B)). The tempe rature dependence of the resistivity was measured for the compounds wi th M = Si, Mn, Fe, and Co.