Effects of cations upon absorption spectra. Part 1.—Tetrahedral bromo and iodo complexes of nickel(II) in acetone

Abstract

The formation of the tetrahedral complexes [NiBr₃(solvent)]^–, NiBr^2–₄, [NiI₃(solvent)]^– and NiI^2–₄ in acetone in the presence of the bromides and iodides of lithium and various quaternary ammonium cations has been investigated. The tri-halogeno species is unaffected by the counter ion but the extent of formation of the tetra-halogeno species is dependent upon the size of the counter ion: the results with lithium are anomalous. The data is interpreted in terms of the presence of the solvent-shared ion pair [NiX₄(solvent)R₄N]^–. An explanation of the lithium results is given. In solutions containing only nickel, bromide and the counter ion, and at Br/Ni mole ratios in excess of 3 the two species equilibrium tri ⇌ tetra is established; when perchlorate is also present at least one octahedral species is always evident.