Effects of cations upon absorption spectra. Part 4.—Octahedral-tetrahedral equilibria between chloro-nickel(II) complexes in ethylene glycol and glycerol

Abstract

The various chloro-nickel(II) complexes formed in ethylene glycol and glycerol as the concentration of added chloride and the temperature is increased are identified. With all the chlorides investigated, except lithium, the species Ni(solvent)2+x, NiCl(solvent)+y and NiCl2–4 are obtained in ethylene glycol: x is a number between 3 and 6, and y a number between 3 and 5, since ethylene glycol is potentially a bidentate ligand. In the presence of lithium chloride the above specices and NiCl2(solvent)z, where z can be 2, 3 or 4, and NiCl3(solvent)– are detected. In glycerol, the same situation obtains but, since glycerol is potentially tridentate, the various species are written Ni(solvent)2+p, p being 2–6; NiCl(solvent)+q, q being 2–5; and NiCl2(solvent)r, r being 2–4. An octahedral arrangement of chlorine and oxygen is always maintained around nickel except in NiCl2–4 and NiCl3(solvent)–where the arrangement is tetrahedral. An equilibrium between monochloro species and NiCl2–4 is observed with all chlorides, except lithium, in ethylene glycol and glycerol, and ΔH is +14 ± 1 and +15 ± 1 kcal/mol and ΔS+ 41 and +42 cal/mol deg., respectively.