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

Single crystals of CaAl 2 Pt 2 , Ca 2 Al 3 Pt and Ca 2 AlPt 2 were initially observed in an attempt to synthesize Ca 3 Al 4 Pt 4 . Their structures were determined using single‐crystal X‐ray diffraction experiments. While nominal CaAl 2 Pt 2 (CaBe 2 Ge 2 type, P 4/ nmm , a =426.79(2), c =988.79(6) pm, w R 2 =0.0679, 246 F 2 values and 18 variables) and Ca 2 Al 3 Pt (Mg 2 Cu 3 Si type, P 6 3 / mmc , a =561.46(5), c =876.94(8) pm, w R 2 =0.0664, 214 F 2 values and 13 variables) exhibit Al/Pt mixing, for Ca 2 AlPt 2 (Ca 2 Ir 2 Si type, C 2/ c , a =981.03(2) b =573.74(1), c =772.95(2) pm, β =101.862(1)° w R 2 =0.0307, 2246 F 2 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 CaAl 2 Pt 2 and Ca 2 Al 3 Pt always multi‐phase mixtures were observed while Ca 2 AlPt 2 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 [Al x Pt y ] δ − polyanion and Ca δ + cations in the cavities of the polyanions.