Ca5Rh and Ca5Ir:: Isotypic compounds with a new structure type

The synthesis and the crystal structure of two new intermetallic phases with formula Ca5Rh and Ca5Ir are reported. The two compounds are isotypic and crystallize with a new structure type. The crystal structure, elucidated by single-crystal X-ray techniques for the iridium compound and confirmed for Ca5Rh by powder data, is orthorhombic, oP24-Pnma, Z = 4. The lattice constants, as obtained from Guinier powder patterns are: a = 7.655(3) angstrom, b = 15.878(6) angstrom and c = 6.786(2) angstrom for Ca5Ir and a = 7.569(3) angstrom, b = 16.067(10) angstrom and c = 6.725(3) angstrom for Ca5Rh. Apart for the 9:1 phase found in several M-X systems (M = Ca, Sr, Eu; X = Rh, Ir, Pd, Pt), whose structure, however, has not yet been solved, the 5:1 composition represents the M-richest composition so far observed in such systems. (C) 2006 Elsevier B.V. All rights reserved.