New class of oligonuclear platinum-thallium compounds with a direct metal-metal bond. 2. Structural characterization of the complexes

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-T1(CN)(n-1)]((n-1)-) (n = 1-4 for compound I, II, III, and IV, respectively) was determined by means of multinuclear NMR (Pt-195, Tl-205, C-13) 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 Pt-195-Tl-205 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.