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A new series of four binuclear platinum-thallium cyano compounds containing a direct and unsupported by ligands metal-metal bond has been prepared in aqueous solution. The structure of these compounds represented by the formula [(NC) 5 Pt-Tl(CN) n-1 ] (n-1)-(n ) 1-4 for compound I, II, III, and IV, respectively) was determined by means of multinuclear NMR ( 195 Pt, 205 Tl, 13 C) supported by Raman spectroscopy. In addition, a trinuclear complex with the formula [(NC) 5 Pt-Tl-Pt(CN) 5 ] 3-is formed in solutions where the Pt/Tl ratio is larger than 1. The compounds exhibit very large one-bond 195 Pt-205 Tl spin-spin coupling constants, 25-71 kHz; the value for compound I, 71 060 Hz, is the largest reported coupling constant between two different nuclei. The possible reasons for this strong coupling, as well as its variation along the series of the binuclear compounds I-IV, are discussed in terms of the metal-metal bond strength, varying participation of s-electrons in this bond and oxidation state of the metal ions.

The structures of three closely related heterodimetallic cyano complexes, [(NC)(5)Pt-Tl(CN)(n)()](n)()(-) (n = 1-3), formed in reactions between [Pt(II)(CN)(4)](2)(-) and Tl(III) cyano complexes, have been studied in aqueous solution. Multinuclear NMR data ((205)Tl, (195)Pt, and (13)C) were used for identification and quantitative analysis. X-ray absorption spectra were recorded at the Pt and Tl L(III) edges. The EXAFS data show, after developing a model describing the extensive multiple scattering within the linearly coordinated cyano ligands, short Pt-Tl bond distances in the [(NC)(5)Pt-Tl(CN)(n)()](n)()(-) complexes: 2.60(1), 2.62(1), and 2.64(1) A for n = 1-3, respectively. Thus, the Pt-Tl bond distance increases with increasing number of cyano ligands on the thallium atom. In all three complexes the thallium atom and five cyano ligands, with a mean Pt-C distance of 2.00-2.01 A, octahedrally coordinate the platinum atom. In the hydrated [(NC)(5)Pt-Tl(CN)(H(2)O)(4)](-) species the thallium atom coordinates one cyano ligand, probably as a linear Pt-Tl-CN entity with a Tl-C bond distance of 2.13(1) A, and possibly four loosely bound water molecules with a mean Tl-O bond distance of about 2.51 A. In the [(NC)(5)Pt-Tl(CN)(2)](2)(-) species, the thallium atom probably coordinates the cyano ligands trigonally with two Tl-C bond distances at 2.20(2) A, and in [(NC)(5)Pt-Tl(CN)(3)](3)(-) Tl coordinates tetrahedrally with three Tl-C distances at 2.22(2) A. EXAFS data were reevaluated for previously studied mononuclear thallium(III)-cyano complexes in aqueous solution, [Tl(CN)(2)(H(2)O)(4)](+), [Tl(CN)(3)(H(2)O)], and [Tl(CN)(4)](-), and also for the solid K[Tl(CN)(4)] compound. A comparison shows that the Tl-C bond distances are longer in the dinuclear complexes [(NC)(5)Pt-Tl(CN)(n)()](n)()(-) (n = 1-3) for the same coordination number. Relative oxidation states of the metal atoms were estimated from their (195)Pt and (205)Tl chemical shifts, confirming that the [(NC)(5)Pt-Tl(CN)(n)()](n)()(-) complexes can be considered as metastable intermediates in a two-electron-transfer redox reaction from platinum(II) to thallium(III). Vibrational spectra were recorded and force constants from normal-coordinate analyses are used for discussing the delocalized bonding in these species.

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In contrast to what is usually assumed, we have found and proved that thallium(III) forms very strong cyanide complexes in aqueous solution. We have investigated this system using 205T1,13C, and 14N NMR and potentiometry and established the existence of four thallium(III)-cyanide complexes of the composition T1(CN)"3"", = 1-4. We have measured their chemical shifts and spin-spin coupling constants and determined their formation constants at 25 °C in dilute (0.05 M) aqueous solution in the ionic medium ([Na+] = 1 M, [Li+] + [H+] = 3 M, [C104"] = 4 M). The overall formation constants are log ß = 13.2 (1), log ß2 = 26.5 (2), log ß2 = 35.2 (2), and log = 42.6 (2). We have also determined the stability constant for HCN in the same ionic medium, log K" = 10.11 (5). One-bond spin-spin coupling constants between thallium and carbon, 1/(205T1-13C), for the mono-and dicyano complexes of thallium(III) are 14636 and 13749 Hz, respectively, and appear to be the largest known coupling constants between these nuclei. The stability of the T1(CN)"3"" complexes is discussed in terms of their kinetic inertness.

Rates and mechanisms of fluoride exchange reactions between various uranyl fluoro complexes {UO2(H2O)5 - n F n 2- n }, and HF/F- have been studied in aqueous solution using 19F and 17O NMR line broadening technique. A group of 15 different exchange pathways has been identified, and their rate laws and rate constants have been determined. All reactions are first order with regard to the uranyl complex and second order overall. Two pathways dominate:  fluoride exchange between two uranyl complexes, presumably through the formation of a fluoride bridging intermediate/transition state, e.g., UO2F+ + UO2*F2 ⇌ UO2F*F + UO2F+ (k 1,2), and fluoride exchange between a uranyl complex and F-/HF, e.g., UO2F+ + H*F ⇌ UO2*F+ + HF (k 1,HF). The exchange between UO2 2+ and UO2F+ takes place mainly according to UO2 2+ + HF ⇌ UO2F+ + H+ (forward, k‘0,HF; reverse, k 1,HF). Most of these reactions have rate constants, k m,n ≈ 5 × 104 M-1 s-1, at −5 °C. The exchange reactions seem to follow the Eigen−Wilkins mechanism, where the rate determining step is a ligand promoted dissociation of coordinated water. The exchanges involving UO2F n 2- n , n = 4 and 5, are much faster than the others, indicating mechanistic differences. The exchange rate was approximately 3 times faster for reactions involving DF than for HF. The activation parameters have been determined for two reaction pathways.

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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.