New Class of Oligonuclear Platinum−Thallium Compounds with a Direct Metal-Metal Bond. 5. Structure Determination of Heterodimetallic Cyano Complexes in Aqueous Solution by EXAFS and Vibrational Spectroscopy

Abstract

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.

Au3-to-Ag3coordinate-covalent bonding and other supramolecular interactions with covalent bonding strength

“…Tz)] 3 , blue regions) during the stacking process and quite small formation energies of $3 kcal mol À1 . Notwithstanding the small magnitude of each constituent force, the overall dimer-of-trimer stabilization magnitude of $65 kcal mol À1 herein is even stronger than those in literature precedents of largely undisputed intermolecular covalent bonds, such as those in d 1 -d 1 or d 9 -d 9 ground-state single bonds, 3 P g or 3 S u + excited-state single bonds in the Hg 2 excimer, or singlet (or triplet) p-stacked pyrene 2 sandwiched excimersall of which attain D e values in the #50 kcal mol À1 range 41,[46][47][48][49][50][51]. The stabilization herein is likewise $2Â higher than that in the claimed polar-covalent bonding reported recently in a heterobimetallic Au 2 CuIm 2 Pz complex (D e ¼ $35-40 kcal mol À1 ).…”

All That Glitters Is Not Gold: A Computational Study of Covalent vs Metallophilic Bonding in Bimetallic Complexes of d10 Metal Centers—A Tribute to Al Cotton on the Tenth Anniversary of His Passing

“…The M-M' systems herein are akin to other systems shown in the literature with varying degrees of metal-metal distances and deviations in geometryone in particular showing rather strong Pt(II)-Tl(III) polar-covalent bonding in [(NC) 5 Pt-Tl(CN) n ] n -complexes discovered by Glaser and co-workers that possess short intramolecular M-M' distances; subsequent computational studies completed by Pyykkö and Patzschke supported the polar-covalent bond argument. [79,80] In Glaser's complexes, the Pt(II)-Tl(III) centers exhibit a difference in electronegativity with corresponding orbital energy mismatch, leading to a significant shortening of M-M' distances. For the closed-shell metal center complexes herein, on the other hand, d 10 All That Glitters Is Not Gold of the lighter metal center to the Au(I) organometallic center, leading to short intramolecular M-M' distances.…”

Solvent Effects on 195Pt and 205Tl NMR Chemical Shifts of the Complexes [(NC)5PtTl(CN)n]n− (n=0–3), and [(NC)5PtTlPt(CN)5]3− Studied by Relativistic Density Functional Theory

“…Solvent effects have been taken into account by using two different approaches. In solution, complexes I , II , III , and V are moderately strongly coordinated by water molecules 3. 10 This first (solvation or coordination) water shell is represented in the computation by explicitly adding water molecules to surround the Tl atom.…”