Synthesis,Structure, Chemical Bonding,and Properties of CaTIn2 (T = Pd,Pt, Au)

The new compounds CaPdIn₂, CaPtIn₂, and CaAuIn₂ were prepared from the elements by reaction in glassy carbon crucibles under flowing argon. They crystallize with the MgCuAl₂ structure type (space group Cmcm), a ternary ordered version of the Re₃B type. The three crystal structures were refined from single‐crystal four‐circle diffractometer data: a = 444.35(7), b = 1038.0(1), c = 781.32(9), wR2 = 0.1352, 455 F² values for CaPdIn₂, a = 439.65(7), b = 1043.8(1), c = 781.22(8) pm, wR2 = 0.0368, 462 F² values for CaPtIn₂, and a = 456.35(5), b = 1074.8(1), c = 759.69(8) pm, wR2 = 0.0640, 763 F² values for CaAuIn₂, with Z = 4 and 16 parameters for each refinement. Structural elements of these compounds are transition metal (T) centered trigonal prisms formed by the calcium and indium atoms. The transition metal and indium atoms form three‐dimensionally infinite TIn₂] polyanions in which the calcium atoms occupy pentagonal channels. First principles calculations of the electronic structures of these materials strongly suggest the idea of an In–In bonded three‐dimensional network. Theoretical charge density as well as COHP analyses reveal that the calcium atom in CaAuIn₂ (isotypic with NaAuIn₂) has not completely lost its two valence electrons. Magnetic susceptibility measurements of compact polycrystalline samples of CaPdIn₂, CaPtIn₂, and CaAuIn₂ indicate weak Pauli paramagnetism. The compounds are metallic conductors with room temperature values for the specific resistivities of 35 ± 10, 20 ± 10, and 25 ± 10 μ Ωcm for CaPdIn₂, CaPtIn₂, and CaAuIn₂, respectively.