AbstractThe 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 180 pm in CeRu4B4. The intermediate valence of cerium leads to shorter Ce–Ru distances of 292 pm. CeRu4B4 behaves like a Pauli paramagnet with a small room temperature susceptibility of 1.5 × 10–4 emu·mol–1. Chemical bonding analyses shows substantial Ru–B and B–B bonding within the [Ru4B4] substructure.