New Class of Oligonuclear Platinum−Thallium Compounds with a Direct Metal−Metal Bond. 2. Structural Characterization of the Complexes

Abstract

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.

A New Class of Oligonuclear Platinum-Thallium Compounds with a Direct Metal−Metal Bond - 3. Unusual Equilibria in Aqueous Solution

“…However, the structural data discussed in our recent paper [2] show that in all the bimetallic complexes five cyanides are coordinated directly to the Pt-center, and this (NC) 5 PtϪ unit is, in turn, coordinated to the Tl atom. The species [Pt II CN) 5 ] 3Ϫ has not been reported previously and it is likely that it does not exist; accordingly, no formation constant has been measured.…”

“…The trend of the constants follows the normal decrease of the stepwise stability constants, although the decrease is somewhat smaller compared to the corresponding values for the parent complexes, Tl(CN) 2 ϩ (logK 2 ϭ 13.2), Tl(CN) 3 (logK 3 ϭ 8.5). [20] The pronounced weakening of the bond between thallium and cyanide ligands in II and III compared to Tl(CN) 2 ϩ and Tl(CN) 3 , respectively, can be attributed to the strong influence of the (NC) 5 PtϪ unit coordinated to the thallium atom in these complexes.…”

“…Preliminary experiments aimed at finding new complexes [2] indicated that the speciation of the Pt-Tl bimetallic complexes varies at different total concentrations of the . Changing the concentration of any of the components shifted the distribution of the reactants and/or products, and demonstrated the existence of several types of chemical equilibria in the solutions.…”

“…The advantage of these components for a multinuclear NMR study is obvious, all atoms have suitable NMR active nuclei (see in refs. [1] and [2] ). 205 Tl NMR is superior in sensitivity, and its huge chemical shift scale provides slow exchange regimes for the different species, thus allowing to follow the concentration distribution of the formed clusters.…”

“…[4] [5] [6] [7] [8] [9] Recently, we have published a study of new binuclear platinum-thallium cyano compounds containing a direct metalϪmetal bond. [1] Their structure has been studied in solution [2] as well as in the solid state. [10] In the present study a new aspect of these small clustersЈ chemistry is explored, namely their equilibrium behaviour in aqueous solution.…”