The rare earth borides <i>RE</i>Ru₄B₄ (<i>RE</i> = 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, <i>I</i>4₁/<i>acd</i>, <i>a</i> = 747.47(8), <i>c</i> = 1506.4(3) pm, <i>wR</i>₂ = 0.0579, 362 <i>F</i>² values for CeRu₄B₄, <i>a</i> = 751.3(2), <i>c</i> = 1507.1(5) pm, <i>wR</i>₂ = 0.0724, 471 <i>F</i>² values for PrRu₄B₄, <i>a</i> = 751.0(2), <i>c</i> = 1506.9(6) pm, <i>wR</i>₂ = 0.0598, 384 <i>F</i>² values for NdRu₄B₄, and <i>a</i> = 749.1(1), <i>c</i> = 1506.0(3) pm, <i>wR</i>₂ = 0.0759, 413 <i>F</i>² values for SmRu₄B₄, with 18 variables per refinement. Striking structural motifs of the <i>RE</i>Ru₄B₄ 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<b>·</b>mol^-1. Chemical bonding analyses shows substantial Ru-B and B-B bonding within the [Ru₄B₄] substructure.Read less <