Structure refinement of quaternary RE-B-C-Si compounds: Y_3−x(B₁₂)₃(CSi)Si₈ (x ≈ 0.96) and Dy_3−x(B₁₂)₃(CSi)Si₈ (x ≈ 0.90)

We refined the crystal structure of quaternary RE-B-C-Si (RE = Y or Dy) compounds Y_3-x(B₁₂)₃(CSi)Si₈ (x ≈ 0.96) and Dy_3-x(B₁₂)₃(CSi)Si₈ (x ≈ 0.90). Both compounds have a trigonal crystal structure with space group Rm (No. 166). They have previously been assigned as ternary RE-B-Si compounds, but we incorporated carbon to the new structure refinements. The refinement for Y_3-x(B₁₂)₃(CSi)Si₈ achieved a final R1 = 0.0288 for 1178 independent reflections with F₀ > 4σ(F₀) and 0.0431 for all 1484 reflections, and the refinement for Dy_3-x(B₁₂)₃(CSi)Si₈ achieved a final R1= 0.0382 for 2009 independent reflections with F₀ > 4σ(F₀) and 0.0385 for all 2022 reflections. The new structure refinements suggest the presence of (B₁₂)₃-Si-C-(B₁₂)₃ units, which, together with two other units, B₁₂ icosahedron cluster and Si₈ ethane-like cluster, stabilize the RE_3-x(B₁₂)₃(CSi)Si₈ crystal structure.