The ternary platinides CaGa₅Pt₃ and EuGa₅Pt₃

Abstract

Abstract The ternary platinides CaGa 5 Pt 3 ( a = 2082.5(4), b = 406.05(8), c = 739.2(1) pm) and EuGa 5 Pt 3 ( a = 2085.5(5), b = 412.75(9), c = 738.7(1) pm) were synthesized from the elements in sealed high-melting metal tubes in an induction furnace. CaGa 5 Pt 3 and EuGa 5 Pt 3 are isotypic with CeAl 5 Pt 3 and isopointal with the YNi 5 Si 3 type intermetallic phases (space group Pnma , oP 36 and Wyckoff sequence c 9 ). The structure of EuGa 5 Pt 3 was refined from single crystal X-ray diffractometer data: w R 2 = 0.0443, 1063 F 2 values and 56 variables. The gallium and platinum atoms build up a three-dimensional [Ga 5 Pt 3 ] 2− polyanionic network in which the europium atoms fill slightly distorted hexagonal prismatic voids. The Ga–Pt distances within the network range from 249 to 271 pm, emphasizing the covalent bonding character. Temperature dependent magnetic susceptibility measurements indicate diamagnetism for CaGa 5 Pt 3 and isotypic BaGa 5 Pt 3 . EuGa 5 Pt 3 behaves like a Curie–Weiss paramagnet above 50 K with an experimental magnetic moment of 8.17(1) µ B /Eu atom, indicating divalent europium. Antiferromagnetic ordering sets in at T N = 8.5(1) K. The divalent ground state of europium is confirmed by 151 Eu Mössbauer spectroscopy. EuGa 5 Pt 3 shows a single signal at 78 K with an isomer shift of −9.89(4) mm s −1 . Full magnetic hyperfine splitting with a hyperfine field of 25.0(2) T is observed at 6 K in the magnetically ordered regime.