New rhodium-rich germanides RERh₆Ge₄ (RE = Y, La, Pr, Nd, Sm-Lu)

The ternary germanides RERh₆Ge₄ (RE = Y, La, Pr, Nd, Sm-Lu) were obtained by arc-melting of the elements and subsequent annealing. Single crystals were grown from bismuth fluxes. The samples were studied by X-ray diffraction on powders. The structures of five members were refined from single crystal diffraction data: LiCo₆P₄ type, P anti 6m2, a = 715.8(1), c = 387.33(8) pm, wR = 0.0238, 332 F² values for LaRh₆Ge₄, a = 715.0(1), c = 384.96(7) pm, wR = 0.0211, 329 F² values for PrRh₆Ge₄, a = 714.28(9), c = 382.57(6) pm, wR = 0.0136, 327 F² values for SmRh₆Ge₄, a = 714.2(1), c = 381.6(1), wR = 0.0270, 327 F² values for GdRh₆Ge₄, and a = 714.2(2), c = 379.0(1) pm, wR = 0.0273, 324 F² values for HoRh₆Ge₄ with 19 variables per refinement. The RERh₆Ge₄ structures have two crystallographically independent germanium sites in trigonal prismatic coordination, manifesting the close structural relationship with metal-rich phosphides. Together, the rhodium and germanium atoms build up three-dimensional [Rh₆Ge₄] networks, which leave large channels for the rare earth atoms. Each rare earth atom has coordination number 20 with 12 Rh, 6 Ge, and 2 RE neighbors. Temperature dependent magnetic susceptibility measurements indicate Pauli paramagnetic behavior for YRh₆Ge₄, LaRh₆Ge₄, and LuRh₆Ge₄. The compounds RERh₆Ge₄ (RE = Gd-Yb) are Curie-Weiss paramagnets. Antiferromagnetic ordering was observed at 8.4(5) K (GdRh₆Ge₄), 13.6(5) K (TbRh₆Ge₄), 5.1(5) K (DyRh₆Ge₄), and 8.9(5) K (YbRh₆Ge₄). DyRh₆Ge₄ and YbRh₆Ge₄ show metamagnetic transitions at 2.5(5) and 45(2) kOe, respectively. (Copyright copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)