Nominal CaAl2Pt2 and Ca2Al3Pt – two new intermetallic compounds in the ternary system Ca–Al–Pt

Abstract

Single crystals of CaAl2Pt2, Ca2Al3Pt and Ca2AlPt2 were initially observed in an attempt to synthesize Ca3Al4Pt4. Their structures were determined using single‐crystal X‐ray diffraction experiments. While nominal CaAl2Pt2 (CaBe2Ge2 type, P4/nmm, a = 426.79(2), c = 988.79(6) pm, wR2 = 0.0679, 246 F2 values and 18 variables) and Ca2Al3Pt (Mg2Cu3Si type, P63/mmc, a = 561.46(5), c = 876.94(8) pm, wR2 = 0.0664, 214 F2 values and 13 variables) exhibit Al/Pt mixing, for Ca2AlPt2 (Ca2Ir2Si type, C2/c, a = 981.03(2) b = 573.74(1), c = 772.95(2) pm, β = 101.862(1)° wR2 = 0.0307, 2246 F2 values and 25 variables) no mixing was observed. Subsequently, the nominal compositions were targeted with synthetic attempts from the elements using arc‐melting and annealing techniques. For CaAl2Pt2 and Ca2Al3Pt always multi‐phase mixtures were observed while Ca2AlPt2 could be obtained as almost X‐ray pure material. Quantum‐chemical calculations were used to investigate the charge transfer in these compounds rendering them polar intermetallics with a designated [AlxPty]δ– polyanion and Caδ+ cations in the cavities of the polyanions.