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, MgCuAl(2) type (Cmcm, Z = 4, a = 4.486(2), 4.491(3) A, b = 10.991(5), 10.990(6) A, c = 8.154(1), 8.140(4) A for SrPdTl(2), and SrPtTl(2), respectively). The structure can be directly derived from that of hexagonal SrTl(2) (CaIn(2) type) in which four-bonded 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 SrTl(2) and SrPdTl(2) demonstrate the effects of the conversion, with strong Pd-Tl bonding and appreciable electron transfer from Tl to Pd. Property measurements show that SrPdTl(2) is metallic, as expected.