ELECTROCHEMICALLY GENERATED COPPER(II), TIN(II), BISMUTH(III) AND ZINC(II) COMPLEXES IN DICHLOROMETHANE CONTAINING TETRABUTYLAMMONIUM PERCHLORATE, TETRAFLUOROBORATE OR HEXAFLUOROPHOSPHATE AS THE ELECTROLYTE

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][ClO4] 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 solvents 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.