Synthesis, Structure, and Properties of the New Intermetallic Compounds SrPdTl2 and SrPtTl2

The title compounds have been synthesized and characterized structurally and through property measurements and electronic structure calculations. Single-crystal X-ray diffraction analyses reveal that the two compounds crystallize in an orthorhombic system, MgCuAl2 type (Cmcm, Z = 4, a = 4.486(2), 4.491(3) (angstrom), b = 10.991(5), 10.990(6) (angstrom), c = 8.154(1), 8.140(4) (angstrom) for SrPdTl2, and SrPtTl2, respectively). The structure can be directly derived from that of hexagonal SrTl2 (CaIn2 type) in which fourbonded thallium atoms in shared puckered hexagons generate tunnels. The Pd or Pt is encapsulated (with symmetry reduction) on the side of each tunnel within a distorted trigonal prism. Band structure calculations (EHTB) on both SrTl2 and SrPdTl2 demonstrate the effects of the conversion, with strong Pd-Tl bonding and appreciable electron transfer from Tl to Pd. Property measurements show that SrPdTl2 is metallic, as expected.