Octahedral–tetrahedral co-ordination equilibria of cobalt(II) and nickel(II) chlorides in non-aqueous solvents containing mercuric chloride or aluminium trichloride

Abstract

Addition of mercuric chloride to a solution of cobalt(II) chloride in acetonitrile assists in the formation of the pink octahedral complex (CoCl,5CH₃CN)⁺ which on being heated, accepts chloride to form the blue tetrahedral complex CoCl₂,2CH₃CN. Addition of aluminium trichloride to nickel(II) chloride solution in dimethylformamide aids the formation of tetrahedral species particularly at high temperatures. At a little below room temperature octahedral species are formed. Equilibrium constants, heats of reaction, and enthalpy and entropy changes for these halide-ion transfer equilibria have been evaluated.