The germanides APtGe2 (A = Ca, Sr, Eu)

Abstract The germanides A PtGe 2 ( A = Ca, Sr, Eu) were synthesized from the elements in sealed tantalum ampoules in an induction furnace followed by annealing. The polycrystalline samples were characterized by powder X-ray diffraction (Guinier patterns). The structures of CaPtGe 2 (CeRhSn 2 type, Cmcm , a = 443.45(3), b = 1593.03(12), c = 886.15(6) pm, wR = 0.0464, 673 F 2 values, 30 variables) and EuPt 1.043(5) Ge 1.957(5) (CeNiSi 2 type, Cmcm , a = 445.23(4), b = 1752.5(2), c = 429.63(4) pm, wR = 0.0415, 389 F 2 values, 19 variables) were refined from single crystal X-ray diffractometer data. One of the germanium site in EuPt 1.043(5) Ge 1.957(5) showed a small Ge/Pt mixed occupancy. SrPtGe 2 ( a = 451.13(6), b = 1764.8(2), c = 429.60(5) pm) is isotypic with EuPtGe 2 . The platinum atoms in both germanides have trigonal prismatic coordination: Pt@Ca 4 Ge 2 and Pt@Eu 4 Ge 2 . The germanium substructures differ significantly: Ge 2 dumb-bells with 246 and 262 pm Ge–Ge distances in CaPtGe 2 versus germanium zig-zag chains (253 pm Ge–Ge distances) and a distorted square net (309 pm Ge–Ge distances) in EuPtGe 2 . CaPtGe 2 and SrPtGe 2 are diamagnetic. EuPtGe 2 is a Curie–Weiss paramagnet with an experimental magnetic moment of 7.88(1) µ B Eu atom −1 . The purely divalent character of europium is manifested by a single signal at δ = −11.38(1) mm s −1 in the 151 Eu Mössbauer spectrum at 78 K. EuPtGe 2 orders antiferromagnetically at T N = 5.4(1) K.