The structures of three closely related heterodimetallic cyano complexes, [(NC)5Pt-Tl(CN)n]n- (n = 1-3), formed in reactions between [PtII(CN)4]2- and TlIII cyano complexes, have been studied in aqueous solution. Multinuclear NMR data (205Tl, 195Pt, and 13C) were used for identification and quantitative analysis. X-ray absorption spectra were recorded at the Pt and Tl LIII 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)5Pt-Tl(CN)n]n- complexes: 2.60(1), 2.62(1), and 2.64(1) Å 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 Å, octahedrally coordinate the platinum atom. In the hydrated [(NC)5Pt-Tl(CN)(H2O)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) Å, and possibly four loosely bound water molecules with a mean Tl-O bond distance of about 2.51 Å. In the [(NC)5Pt-Tl(CN)2]2- species, the thallium atom probably coordinates the cyano ligands trigonally with two Tl-C bond distances at 2.20(2) Å, and in [(NC)5Pt-Tl(CN)3]3- Tl coordinates tetrahedrally with three Tl-C distances at 2.22(2) Å. EXAFS data were reevaluated for previously studied mononuclear thallium(III)-cyano complexes in aqueous solution, [Tl(CN)2(H2O)4]+, [Tl(CN)3(H2O)], 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)5Pt-Tl(CN)n]n- (n = 1-3) for the same coordination number. Relative oxidation states of the metal atoms were estimated from their 195Pt and 205Tl chemical shifts, confirming that the [(NC)5Pt-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.
2001. Vol. 40, no 16, 3889-99 p.