Synthesis and structure of RhMg3 and Ir3Mg 13

Abstract

The binary transition metal magnesium compounds RhMg3 and Ir3Mg13 have been synthesized from the elements in sealed niobium tubes and investigated on the basis of X-ray powder and single crystal data: Cu3P type, P63cm, a = 790.5(4), c = 825.6(3) pm, wR2 = 0.0244, 344 F2 values, 27 variable parameters for RhMg 3, and R3̄c, a = 1607.0(2), c = 844.88(9) pm, wR2 = 0.0535, 656 F2 values, 29 variable parameters for Ir3Mg13. The rhodium atoms in RhMg3 have coordination number 11. These polyhedra show an AB AB stacking sequence like in the hexagonal close-packed structure. The crystal chemical relation of the Cu3P type structure of RhMg3 with the aristotype Na3As (IrAl3) is discussed on the basis of a group-subgroup scheme. Ir3Mg13 crystallizes with a new complex structure type with coordination numbers of 11, 14, 15, 14, and 12 for the Ir, Mg1, Mg2, Mg3, and Mg4 atoms, respectively.