UNSPECIFIED. (2000) Kinetics and mechanism for reversible chloride transfer between mercury(II) and square-planar platinum(II) chloro ammine, aqua, and sulfoxide complexes. Stabilities, spectra, and reactivities of transient metal-metal bonded platinum-mercury adducts. INORGANIC CHEMISTRY, 39 (19). pp. 4286-4294. ISSN 0020-1669

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Abstract

The Hg-aq(2+)- and HgClaq+-assisted aquations of [PtCl4](2-) (1), [PtCl3(H2O)](-) (2), cis-[PtCl2(H2O)(2)] (3), trans-[PtCl2(H2O)(2)] (4), [PtCl(H2O)(3)](+) (5), [PtCl3Me2SO](-) (6), trans-[PtCl2(H2O)Me2SO] (7), cis-[PtCl(H2O)(2)Me2SO](+) (8), trans-[PtCl(H2O)(2)Me2SO](+) (9), trans-[PtCl2(NH3)(2)] (10), and cis-[PtCl2(NH3)(2)] (11) have been studied at 25.0 degrees C in a 1.00 M HClO4 medium buffered with chloride, using stopped-flow and conventional spectrophotometry. Saturation kinetics and instantaneous, large UV/vis spectral changes on mixing solutions of platinum complex and mercury are ascribed to formation of transient adducts between Hg2+ and several of the platinum complexes. Depending on the limiting rate constants, these adducts are observed for a few milliseconds to a few minutes. Thermodynamic and kinetics data together with the UV/vis spectral changes and DFT calculations indicate that their structures are characterized by axial coordination of Hg to Pt with remarkably short metal-metal bonds. Stability constants for the Hg2+ adducts with complexes 1-6, 10, and 11 are (2.1 +/- 0.4) x 10(4), (8 +/- 1) x 10(2), 94 +/- 6, 13 +/- 2, 5 +/- 2, 60 +/- 6, 387 +/- 2, and 190 +/- 3 M-1, respectively, whereas adduct formation with the sulfoxide complexes 7-9 is too weak to be observed. For analogous platinum(II) complexes, the stabilities of the Pt-Hg adducts increase in the order sulfoxide much less than aqua < ammine complex, reflecting a sensitivity to the pi-acid strength of the Pt ligands. Rate constants for chloride transfer from HgCl+ and HgCl2 to complexes 1-11 have been determined. Second-order rate constants for activation by Hg2+ are practically the same as those for activation by HgCl+ for each of the platinum complexes studied, yet resolved contributions for Hg2+ and HgCl+ reveal that the latter does not form dinuclear adducts of any significant stability. The overall experimental evidence is consistent with a mechanism in which the accumulated Pt(II)-Hg2+ adducts are not reactive intermediates along the reaction coordinate. The aquation process occurs via weaker Pt-Cl-Hg or Pt-Cl-HgCl bridged complexes.

Item Type:	Journal Article
Subjects:	Q Science > QD Chemistry
Journal or Publication Title:	INORGANIC CHEMISTRY
Publisher:	AMER CHEMICAL SOC
ISSN:	0020-1669
Date:	18 September 2000
Volume:	39
Number:	19
Number of Pages:	9
Page Range:	pp. 4286-4294
Identification Number:	10.1021/ic000320j
Publication Status:	Published
URI:	http://wrap.warwick.ac.uk/id/eprint/12947

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