Complex borides RERu4B4 (RE = Ce, Pr, Nd, Sm) - Bonding peculiarities and magnetic properties

Mishra T, Eul M, Matar SF, Pöttgen R

Zusammenfassung

The rare earth borides RERu4B4 (RE = Ce, Pr, Nd, Sm) were synthesized from the elements by arc-melting and their crystal structures were studied on the basis of X-ray powder and single-crystal diffraction: LuRu4B4 type, I41/acd, a = 747.47(8), c = 1506.4(3)pm, wR2 = 0.0579, 362 F2 values for CeRu4B4, a = 751.3(2), c = 1507.1(5)pm, wR2 = 0.0724, 471 F2 values for PrRu4B4, a = 751.0(2), c = 1506.9(6)pm, wR2 = 0.0598, 384 F2 values for NdRu4B4, and a = 749.1(1), c = 1506.0(3)pm, wR2 = 0.0759, 413 F2 values for SmRu4B4, with 18 variables per refinement. Striking structural motifs of the RERu4B4 structures are Ru4 tetrahedra and B2 dumbbells with Ru-Ru and B-B distances of 271 and 180pm in CeRu4B4. The intermediate valence of cerium leads to shorter Ce-Ru distances of 292pm. CeRu4B4 behaves like a Pauli paramagnet with a small room temperature susceptibility of 1.5×10-4emu·mol-1. Chemical bonding analyses shows substantial Ru-B and B-B bonding within the [Ru4B4] substructure.