PREPARATION, PROPERTIES AND CRYSTAL-STRUCTURES OF THE THORIUM CHROMIUM BORIDES THCRB4 AND THCR2B6 - STRUCTURE REFINEMENTS OF CECR2B6, THB4 AND THB6

The new polyborides ThCrB4 and ThCr2B6 were prepared by are melting of the elemental components, and their crystal structures were determine d from single-crystal X-ray data. ThCrB4 has a YCrB4-type structure: P bam, a = 605.8(1) pm, b = 1171.2(2) pm, c = 364.0(1) pm, R = 0.024 for 714 structure factors and 26 variable parameters. ThCr2B6 is isotypic with CeCr2B6: Immm, a = 315.8(1) pm, b = 659.1(1) pm, c = 836.4(2) pm , R = 0.030 (415 F values, 14 variables). The structures of the boride s CeCr2B6, ThB4 and ThB6 were refined from single-crystal X-ray data. The B-B bonds between the B-6 octahedra of ThB4 and ThB6 are considera bly shorter than those within the octahedra. ThCrB4, ThCr2B6 and CeCr2 B6 are metallic conductors and Pauli paramagnetic.