Tl-Pt(CN)(5) in the solid state - A multimethod study of an unusual compound containing inorganic wires

The crystal and molecular structure of a polycrystalline powder with a meta l-metal bond and the composition TlPt(CN)(5) has been determined by combini ng results from X-ray powder diffraction (XRD), extended X-ray absorption f ine structure (EXAFS) and vibrational spectroscopic studies. The XRD data g ave the tetragonal space group P4/nmm (No. 129). with a = 7.647(3), c = 8.0 49(3) Angstrom, Z = 2, and well-determined positions of the heavy metal ato ms. The Pt-Tl bond length in the compound is 2.627(2) Angstrom. The platinu m atom coordinates four equivalent equatorial cyano ligands, with a fifth a xial CN ligand and a thallium atom completing a distorted octahedral coordi nation geometry. The Tl-Pt(CN)(5) entities are linked together in linear -N C-Pt-Tl-NC-Pt-Tl chains through the axial cyano ligand. These linear "wires " are the essential structural features and influence the properties of the com-pound. A three-dimensional network is formed by the four equatorial cy ano ligands of the platinum atom that form bridges to the thallium atoms of neighbouring antiparallel chains. The platinum atom and the five nitrogen atoms from the bridging cyano groups form a distorted octahedron around the thallium atom. EXAFS data were recorded at the Pt and Tl L-III edges for a more complete description of the local structure around the Pt and Tl atom s. The excessive multiple scattering was evaluated by means of the FEFF pro gram. Raman and infrared absorption spectroscopy reveal strong coupling of the vibrational modes of the TlPt(CN)(5) entities, in particular the metal - metal stretching mode, which is split into four Raman and two IR bands. F actor group theory shows that a structural unit larger than the crystallogr aphic unit cell must be used to assign vibrational bands. Intra- and interm olecular force constants have also been calculated. The compound exhibits r ed luminescence at 700+/- 3 nm in glycerol and has a corresponding excitati on maximum at 240 nm. X-ray photoelectron spectra (XPS) show that the metal atoms have intermediate oxidation states, Pt3.2+ and Tl1.6+, between those in the parent Pt-II and Tl-III species and the decomposition products, Pt- IV and Tl-I. The solid compound TlPt(CN)(5) is stable to 520 degreesC. Howe ver in presence of water, a two-electron transfer between the metal atoms r esults in the cleavage of the metal-metal bond at 80 degreesC, forming a Pt -IV pentacyanohydrate complex and a monovalent thallium ion.