Synthesis, structure, chemical bonding, and properties of CaTIn2 (T = Pd, Pt, Au)

The new compounds CaPdIn2, CaPtIn2, and Ca\AuIn2 were prepared from the ele ments by reaction in glassy carbon crucibles under flowing argon. They crys tallize with the MgCuAl2 structure type (space group Cmcm), a ternary order ed 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, 55 F-2 values for CaPdIn2, a = 439.65(7), b = 1043.8(1), c = 781.22(8) pm, wR2 = 0.0368, 462 F-2 values for CaPtIn2, and a = 456.35(5), b = 1074.8(1), c = 759.69(8) pm, wR2=0.0640, 763F(2) val ues for CaAuIn2. with Z=4 and 16 parameters for each refinement. Structural elements of these compounds are transition metal (T) centered trigonal pri sms formed by the calcium and indium atoms. The transition metal and indium atoms form three-dimensionally infinite [TIn2] polyanions in which the cal cium atoms occupy pentagonal channels. First principles calculations of the electronic structures of these materials strongly suggest the idea of an I n-In bonded three-dimensional network. Theoretical charge density as well a s COHP analyses reveal that the calcium atom in CaAuIn2 (isotypic with NaAu In2) has not completely lost its two valence electrons. Magnetic susceptibi lity measurements of compact polycrystalline samples of CaPdln(2), CaPtIn2, and CaAuIn2 indicate weak Pauli paramagnetism. The compounds are metallic conductors with room temperature values for the specific resistivities of 3 5 +/- 10, 20 +/- 10, and 25 +/- 10 mu Omega cm for CaPdIn2, CaPtIn2, and Ca AuIn2, respectively.