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 NiCl^2–₄ 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 NiCl^2–₄ and NiCl₃(solvent)^–where the arrangement is tetrahedral. An equilibrium between monochloro species and NiCl^2–₄ 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.