Synthesis, single-crystal structure refinement and Fe/T site preference in the ternary borides FexT7−xB3 (T = Ru, Rh; 0 < x ≤ 1.5)

Single crystals of the borides FexRh7−xB3 (1 < x < 1.5) and FexRu7 − xB3 (0 < x < 1) have been synthesized by arc-melting the elements in a water-cooled copper crucible under argon atmosphere. The silver-like products, structurally characterized by single-crystal X-ray analysis, adopt the hexagonal Th7Fe3 structure type (space group P63mc, no. 186) with Z = 2. Their structures consist of layers of boron-centered trigonal prisms of rhodium or ruthenium (Rh;Ru) and iron on the one side, and one-dimensional channels of face-sharing octahedral (Rh;Ru)6 clusters on the other. Unlike in FeRh6B3, the iron substitution takes place at two (6c and 2b) of the three available rhodium/ruthenium positions, with a preference for the 6c site in the case of the FexRh7−xB3 compounds but not for FexRu7 − xB3.