Rhodium-rich germanides RERh4Ge2 (RE = Y, Gd–Lu): structure and bonding

The rhodium-rich germanides RERh4Ge2 (RE = Y, Gd–Lu) were synthesized by arc-melting of the elements and subsequent annealing in a muffle furnace. The samples were characterized through Guinier powder patterns. The structures of YRh4Ge2 and TmRh4Ge2 were refined from X-ray single crystal diffractometer data: new type, Pnma, Z = 4, a = 1136.4(2) pm, b = 418.29(5) pm, c = 910.12(9) pm, wR2 = 0.0268, 707 F 2 values for YRh4Ge2 and a = 1131.5(1) pm, b = 416.54(5) pm, c = 908.06(9) pm, wR2 = 0.0276, 719 F 2 values for TmRh4Ge2 with 44 variables per refinement. The two crystallographically independent germanium sites both show distorted trigonal prismatic coordination by four rhodium and two rare earth atoms. The basic structural motifs are double prisms, similar to the structures of ZrFe4Si2 and CeIn4Au2. The shortest interatomic distances are observed for the Rh–Ge contacts within the three-dimensional [Rh4Ge2] polyanionic network which are further stabilized through weak Rh–Rh interactions. The calculations of the electronic structure within DFT done exemplarily for the yttrium compound show an itinerant like weak metal with a low density of states at the Fermi level and intricate chemical bonding due to the presence of two germanium sites interacting with the four rhodium sites