Rare-earth gallium antimonides La13Ga8Sb21 and RE12Ga4Sb23 (RE = La-Nd, Sm): Linking Sb ribbons by Ga-6-rings or Ga-2-pairs

The ternary rare-earth gallium antimonides La13Ga8Sb21 and RE12Ga4Sb23 (RE La-Nd, Sm) have been synthesized through reaction of the elements. The stru ctures of La13Ga8Sb21 (hexagonal, space group D-6h(1)-Pb/mmm, Z = 1, a 17.6 57(2) Angstrom, c = 4.3378(7) Angstrom) and Pr12Ga4Sb23 (orthorhombic, spac e group D-2h(25)-Immm, Z = 2, a 4.2612(3) Angstrom, b = 19.4070(13) Angstro m, c = 26.3972(18) Angstrom) have been determined by single-crystal X-ray d iffraction. Both structures contain groupings of RE6 trigonal prisms that e xtend as columns through sharing of the triangular faces. Isolated trigonal planar GaSb3 units result from centering adjacent trigonal prisms by Ga or Sb atoms. Channels outlined by Sb square ribbons linked through Ga-Ga bond ing enclose the triangular assemblies of trigonal prisms. The Ga-Ga bonding is manifested as Ga-6-rings in La13Ga8Sb21 but as Ga-2-pairs in Pr12Ga4Sb2 3. Structural relationships are described between La13Ga8Sb21 and Ba0.8Hf12 As17.7, and between Pr12Ga4Sb23 and La6MnSb15.