Tl−Pt(CN)5 in the Solid State—A Multimethod Study of an Unusual Compound Containing Inorganic Wires

Abstract

The crystal and molecular structure of a polycrystalline powder with a metal-metal bond and the composition TlPt(CN)5 has been determined by combining results from X-ray powder diffraction (XRD), extended X-ray absorption fine structure (EXAFS) and vibrational spectroscopic studies. The XRD data gave the tetragonal space group P4/nmm (No. 129), with a= 7.647(3), c=8.049(3) A, Z=2, and well-determined positions of the heavy metal atoms. The Pt-TI bond length in the compound is 2.627(2) A. The platinum atom coordinates four equivalent equatorial cyano ligands, with a fifth axial CN ligand and a thallium atom completing a distorted octahedral coordination geometry. The Tl-Pt(CN)5 entities are linked together in linear -NC-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 compound. A three-dimensional network is formed by the four equatorial cyano 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 atoms. The excessive multiple scattering was evaluated by means of the FEFF program. 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. Factor group theory shows that a structural unit larger than the crystallographic unit cell must be used to assign vibrational bands. Intra- and intermolecular force constants have also been calculated. The compound exhibits red luminescence at 700 +/- 3 nm in glycerol and has a corresponding excitation 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 degrees C. However in presence of water, a two-electron transfer between the metal atoms results in the cleavage of the metal-metal bond at 80 degrees C, forming a Pt(IV) pentacyanohydrate complex and a monovalent thallium ion.

Structure Studies of Dimeric [Pt2(CN)10]4- Pentacyanoplatinum(III) and Monomeric Pentacyanoplatinum(IV) Complexes by EXAFS, Vibrational Spectroscopy, and X-ray Crystallography

“…Preparations. Aqueous solutions of the complexes [Pt(CN) 5 (OH)] 2- and [Pt(CN) 5 (H 2 O)] - were obtained as described previously from redox decomposition of the solid TlPt(CN) 5 compound. , The [Pt 2 (CN) 10 ] 4- complex can be prepared in aqueous solution either from a redox reaction occurring between the [Tl III (CN) n ] 3- n and [Pt(CN) 4 ] 2- (in excess) complexes 15 or by photoredox decomposition of a trinuclear [(NC) 5 Pt−Tl−Pt(CN) 5 ] 3- complex in aqueous solution . The [Pt(CN) 5 I] 2- complex was prepared according to a procedure described in the literature .…”

“…Pt L III -edge EXAFS data were collected in transmission mode at the Stanford Synchrotron Radiation Laboratory (SSRL) at the experimental station 4-1. The experimental conditions were similar to those described previously. ,, The energy calibration was made by simultaneously scanning a Pt foil for which the first inflection point was set to 11 564 eV. In the samples containing thallium, the usable range for the Pt L III -edge EXAFS measurements is limited to k ≈15 Å -1 by the Tl L III -edge at 12 658 eV.…”

“…Linear configurations of ligand atoms, as for the cyano ligands, are known to enhance the multiple scattering by forward scattering of the intervening atom . To be able to extract reliable structural parameters from the complexes in the current study, we developed and carefully tested models by means of the ab initio FEFF code, describing the strong multiple scattering as a sum of contributions from separate selected backscattering pathways with a minimum of parameters. , …”

4 Aluminium, gallium, indium and thallium

“…The compound is stable to 520 ЊC! 170 Another equally amazing structure involves four bridging Tl() ions sandwiched by two tetraalkynylplatinate [Pt(CCR) 4 ] 2Ϫ fragments. Each Tl() was sited away from the Pt fragments and interacted asymmetrically with four alkynyl ligands, the bonding was described as {µ 3 -η 2 :σ-Pt:η 2 (Tl,Tl)}, forming an approximately square-pyramidal geometry with the TI at the apex.…”

16 The noble metals

“…If water is present the compound becomes Tl[Pt(CN) 5 (H 2 O)]. 179 In parallel work, using EXAFS methods on Tl()-Pt() cyanide complexes showed that the Pt-Tl bonds were about 262 pm long, while 13 C, 195 Pt and 203 Tl NMR spectra showed that a two-electron redox process to Pt() and Tl() occurred in solution with the Pt-Tl complexes as intermediates. 180 Further developments have come from the reactions of various Tl() complexes containing dmso and/or en with [Pt(CN) 4 ] 2Ϫ and cyanide to give such species as [(NC) 5 PtTl(en) 2 ] ϩ with direct Pt-Tl unsupported bonds that are also stable in solution.…”