STRUCTURE, CHEMICAL BONDING, AND PROPERTIES OF COIN3, RHIN3, AND IRIN3

CoIn3, RhIn3, and IrIn3 were synthesized by reacting the elements in s ealed tantalum tubes at 1170 K and subsequent annealing at 718 K, The structures of the three compounds (FeGa3 type, Space group P4(2)/mnm) were refined from single crystal X-ray data: a = 682.82(6), c = 709.08 (7) pm, wR2 = 0.0407, 397 F-2 values for CoIn3, a = 698.28(8), c = 711 .11(9) pm, wR2 = 0.0592, 418 F-2 values for RhIn3, and a = 699.33(5), c = 719.08(5) pm, wR2 = 0.0625, 482 F-2 values for IrIn3 with 16 param eters for each refinement. The structures may be considered as an inte rgrowth of tungsten-like building blocks of indium atoms and AlB2-like slabs of compositions In square Co, In square Rh, and In square Ir, r espectively. These are compared with the related intergrowth var iants found for compounds with ordered U3Si2 and Zr3Al2 type structure. Sem i-empirical band structure calculations for RhIn3 reveal low density-o f-states (DOS) at the Fermi level and negative Rh-Rh crystal orbital o verlap populations (COOP) indicating antibonding Rh-Rh interactions. T he bonding characteristics of CoIn3, RuIn3, and IrIn3 are similar to R hIn3. Magnetic susceptibility measurements of compact polycrystalline samples of CoIn3, RhIn3. and IrIn3 indicate weak Pauli paramagnetism.