High-pressure synthesis and structures of lanthanide germanides of LnGe5 (Ln=Ce, Pr, Nd, and Sm) isotypic with LaGe5

A series of lanthanide penta-germanides LnGe5 (Ln=Ce, Pr, Nd and Sm) has been prepared by high-pressure (5–13 GPa) and high-temperature (500–1200 °C) reaction. CeGe5 crystallizes in an orthorhombic unit cell (S.G. Immm (71)) with a=4.000(5) Å, b=6.192(5) Å, c=9.86(1) Å, and V=244.1(5) Å3. The new germanides are isotypic with LaGe5 consisting of a Ge covalent network with tunnels where guest ions Ln3+ are situated. The network is composed of sublayers with edge-sharing Ge six-membered rings with only boat conformation. The sublayers are connected by rare eight-coordinated Ge atoms. The cell volume of the compounds systematically decreases from La to Sm compounds, except for CeGe5, owing to the lanthanide contraction. The lattice constants of CeGe5 are smaller than those of the Pr compound because it contains Ce4+ ions. CeGe5 is paramagnetic above 2 K, but does not obey the Curie–Weiss law. PrGe5 and NdGe5 are Curie–Weiss type paramagnets with Weiss temperatures of –3.3 and –18.4 K. SmGe5 shows an antiferromagnetic transition at 10.4 K.