Ca 2 RhCd 2 – a primitive orthorhombic superstructure of the W 2 CoB 2 type induced through rhodium-cadmium coloring

The intermetallic compound Ca 2 RhCd 2 was obtained by induction melting ( T = 1,473 K) of the elements in a sealed niobium ampoule followed by annealing in a muffle furnace for one week at 773 K. Ca 2 RhCd 2 (space group Pmmn ) crystallizes with its own structure type, which in fact is a superstructure of the W 2 CoB 2 type (space group Immm ). The crystal structure of Ca 2 RhCd 2 was refined from single-crystal X-ray diffractometer data: a = 892.16(13) pm, b = 460.64(6) pm, c = 584.99(8) pm, wR 2 = 0.0421, 698 F 2 values and 20 variables. The rhodium and cadmium atoms form two-dimensional, planar [RhCd 2 ] δ − polyanionic networks (273–274 pm Rh–Cd) which are separated and charge-balanced by the calcium atoms. The cadmium substructure within the [RhCd 2 ] δ − polyanionic networks consists of covalently bonded zig-zag chains with Cd–Cd distances of 283 pm. The structural relationship with Ca 2 Pd 2 Cd (W 2 B 2 Co type) is discussed on the basis of a group-subgroup scheme.