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 anewstructuretype. 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) Å, b = 15.878(6) Å and c = 6.786(2) Å for Ca5Ir and a = 7.569(3) Å, b = 16.067(10) Å and c = 6.725(3) Å 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