✍ Scribed by Eiki Itabashi; Shigero Ikeda
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It has been shown by several groups of investigators 1 -7 that aqueous solutions of nickel(II) in the presence of pyridine, o-phenylenediamine, ethylenediamine, triethylenetetramine, chloride ion, thiocyanate ion, etc. give a catalytic polarographic wave which occurs at less negative potentials than that for the usual hydrated nickel(II) reduction wave.
The polarographic studies of nickel(II) in the presence of chloride ion have been carried out in both aqueous and acetonitrile media.
In the presence of high concentrations of chloride ion, the reduction wave of nickel(II) shifts to less negative potentials and shows that the electrode reaction takes place with greater reversibility. This behavior has been attributed to the formation and reduction of tetrachloronickel(II) ion 8,9.
Nelson and Iwamoto 6 studied the polarographic behavior of nickel(II) in acetonitrile in the presence of chloride ion, and concluded that nickel(II) in a 0.1 M Et4NC104 electrolyte solution containing ~mall amounts of chloride ion gave a double wave; the first step involved the reversible reduction of the four nickel(II)chloride complexes, NiC1 +, NiCI2, NiClf and NiC12-, and the second step involved the reduction of the hydrated nickel(II). The catalytic nature of the first step was also discussed.
During the study of the effect of the cation of the supporting electrolyte upon the electrode reaction of metal complexes in non-aqueous media 1°'11, it was found that an acetonitrile solution of nickel (II) in the presence of small amounts of chloride, bromide and iodide ions gave a catalytic pre-wave; the activity of halide ions was dependent on the nature of the cation of the supporting electrolyte employed.
The present paper reports on the results of the study on the effect of cations on the catalytic pre-wave of nickel(II) in acetonitrile containing halide ion.
EXPERIMENTAL
Purified acetonitrile was obtained by the procedure given in the previous report 11.
Lithium perchlorate, tetraethylammonium perchlorate (Et4NC104) and tetra-n-butylammonium perchlorate (n-BuaNC104) were prepared by neutralizing the respective hydroxide solutions with dilute perchloric acid. The dried perchlorate
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