Structure,Chemical Bonding and Properties of CoIn3, RhIn3, and IrIn3

CoIn₃, RhIn₃, and IrIn₃ were synthesized by reacting the elements in sealed tantalum tubes at 1170 K and subsequent annealing at 770 K. The structures of the three compounds (FeGa₃ type, space group P4₂/mnm) were refined from single crystal X-ray data: a = 682.82(6), c = 709.08(7) pm, wR2 = 0.0407, 397 F² values for CoIn₃, a = 698.28(8), c = 711.11(9) pm, wR2 = 0.0592, 418 F² values for RhIn₃, and a = 699.33(5), c = 719.08(5) pm, wR2 = 0.0625, 482 F² values for IrIn₃ with 16 parameters for each refinement. The structures may be considered as an intergrowth of tungsten-like building blocks of indium atoms and AlB₂-like slabs of compositions In&Co, In&Rh, and In&Ir, respectively. These are compared with the related intergrowth variants found for compounds with ordered U₃Si₂ and Zr₃Al₂ type structure. Semi-empirical band structure calculations for RhIn₃ reveal low density-of-states (DOS) at the Fermi level and negative Rh–Rh crystal orbital overlap populations (COOP) indicating antibonding Rh–Rh interactions. The bonding characteristics of CoIn₃, RuIn₃, and IrIn₃ are similar to RhIn₃. Magnetic susceptibility measurements of compact polycrystalline samples of CoIn₃, RhIn₃, and IrIn₃ indicate weak Pauli paramagnetism.