Translational symmetries in the linear-chain semiconductors K4[Pt2(P2O5H2) 4X]·nH2O (X = Cl, Br, I)

The solid-state structures of the linear-chain semiconductors K4[Pt2(P2O5H2) 4X]·H2O (X = Cl, Br, I), abbreviated Pt2Cl, Pt2Br, and Pt2I, have been studied. The X-ray crystal structures of Pt2Cl at 300 and 22 K and of Pt2Br at 19 K are reported. These structures show that Pt2Cl is a composite of alternating units of Pt2 and Pt2Cl2 with (AABCCB)n translational symmetry. The X-ray structure of Pt2Br, on the other hand, shows equivalent Pt-Pt bonds and two slightly different Pt-Br bonds. Raman data confirm the composite Pt2/Pt2Cl2 structure for Pt2Cl and indicate that the Pt2Br species is comprised of dimeric units with nearly equal Pt-Pt bonds. The Pt2Br structure is viewed as involving a slight distortion from idealized (AAB)n toward (AABCCB)n translational symmetry. Structural studies of Pt2I were attempted; however, all crystals were twinned. Magnetic susceptibility, microwave conductivity, ESCA, and reflectance spectroscopy measurements are reported for Pt2Br; the material is a semiconductor, with σ = 10-3 Ω-1 cm-1 at 300 K, a bandgap of 0.08 eV, and a bandwidth greater than 0.05 eV. © 1988 American Chemical Society.link_to_subscribed_fulltex