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.