Effects of cations upon absorption spectra. Part 2.—Formation of tetrahedral tetrachloromickelate(II) in aqueous solution

Abstract

The conditions required for the ready conversion of nickel(II) in aqueous solution into the tetrahedral complex tetrachloronickelate(II) are reported, viz., the presence of tetramethylammonium chloride (>5M) and temperatures in excess of 40°C. The corresponding bromo and iodo complexes could not be formed even in saturated solutions of tetramethylammonium bromide and iodide, respectively, at their boiling points. The chloro complex could not be obtained in the presence of tetraethyl and other larger substituted ammonium chlorides nor with alkali and alkaline earth chlorides. The equilibrium [Ni(H₂O)₅CI]⁺(octahedral)⇌ NiCI^2–₄(tetrahedral) was established and ΔH calculated to be 40 ± 2 kcal/mole. The special role of the tetramethylammonium cation is discussed.