Electrochemically generated copper(II), tin(II), bismuth(III) and zinc(II) complexes in dichloromethane containing tetrabutylammonium perchlorate, tetrafluoroborate or hexafluorophosphate as the electrolyte

Abstract

Oxidation of M(amalgam)(M = Cu, Sn, Bi or Zn) electrodes under direct current and differential pulse polarographic or cyclic voltammetric conditions in dichloromethane containing 0.2 mol dm^–3[NBu₄][PF₆], [NBu₄][BF₄] or [NBu₄][CIO₄] as an electrolyte generates weakly solvated and therefore very reactive Cu²⁺, Sn²⁺, Bi³⁺ and Zn²⁺ cations. Since the kinetics of nucleation and precipitation of the usually formed insoluble salts is slow on the voltammetric time-scale, data on the formation of complexes with the electrolyte anions can be obtained. A general order of stability, [PF₆]^–[BF₄]^– < [ClO₄]^–, was found for all metals. However, since the Zn (amalgam)→ Zn²⁺ oxidation process is completely irreversible, quantitative stability constant data on the complexes formed with Zn²⁺ could not be obtained. From these and other data it is concluded that [PF₆]^– generally seems to represent an example of a very weak ligand for metal cations in relatively non-co-ordinating solvent such as dichloromethane. Mechanical transfer of small amounts of metallic Sn and Pb onto a platinum electrode and use of the method of abrasive stripping voltammetry also enabled stability constant data to be obtained. Data for [BF₄]^– complexes with Sn²⁺ and Pb²⁺ thus obtained are in excellent agreement with those derived from the use of amalgam electrodes.