Tb16Br23B4: Endohedrale Bor‐Atome in tetrameren Terbiumclustern

Tb₁₆Br₂₃B₄: Tetrameric Terbium Clusters with Endohedral Boron Atoms The new cluster compound Tb₁₆Br₂₃B₄ was prepared from a stoichiometric mixture of Tb‐metal, TbBr₃ and B‐powder under Ar‐atmosphere in sealed Ta ampoules at 920–950 °C. It crystallizes monoclinic in the space group C2/m with a = 17.523(4) Å, b = 12.008(2) Å, c = 11.901(2) Å und β = 103.95(3)°. In the crystal structure B‐centered Tb₆ octahedra are connected via common edges to form tetrameric units. The Br atoms connect the Tb₁₆B₄‐clusters 3‐dimensionally coordinating the unoccupied edges and corners of the octahedra. Tb₁₆Br₂₃B₄ is a semiconductor with an electrical band gap of E_g = 0.4 eV. The magnetic susceptibility follows a Curie‐Weiss law corresponding to an effective magnetic moment μ_eff = 9.55 μ_B at high temperatures with an antiferromagnetic ordering below 20 K.