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Layered Rare-Earth Gallium Antimonides REGaSb2 (RE = La−Nd, Sm)

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posted on 23.01.2001, 00:00 authored by Allison M. Mills, Arthur Mar
The ternary rare-earth gallium antimonides, REGaSb2 (RE = La−Nd, Sm), have been synthesized through reaction of the elements. The structures of SmGaSb2 (orthorhombic, space group -C2221, Z = 4, a = 4.3087(5) Å, b = 22.093(4) Å, c = 4.3319(4) Å) and NdGaSb2 (tetragonal, space group -I41/amd, Z = 8, a = 4.3486(3) Å, c = 44.579(8) Å) have been determined by single-crystal X-ray diffraction. The SmGaSb2-type structure is adopted for RE = La and Sm, whereas the NdGaSb2-type structure is adopted for RE = Ce−Nd. The layered SmGaSb2 and NdGaSb2 structures are stacking variants of each other. In both structures, two-dimensional layers of composition [GaSb] are separated from square nets of Sb atoms [Sb] by RE atoms. Alternatively, the structures may be considered as resulting from the insertion of zigzag Ga chains between [RE Sb2] slabs. In SmGaSb2, all of the Ga chains are parallel and the [SmSb2] layers are stacked in a ZrSi2-type arrangement. In NdGaSb2, the Ga chains alternate in direction, resulting in a doubling of the long axis relative to SmGaSb2, and the [NdSb2] layers are stacked in a Zr3Al4Si5-type arrangement. Extended Hückel band structure calculations are used to explain the bonding in the [GaSb2]3- substructure.