Relation between the pressure effect and the structure of solvent molecule : pressure effects on the various alcoholic solutions of cobaltous chloride (II) and cobaltous bromide (II)

Cobaltous chloride and cobaltous bromide show blue color in alcohols with the carbon number larger than one. Their absorption spectra have the maxima at 660 mμ and 670 mμ, respetctively. At high pressure, these blue colors disappear and the extent of the pressure effect is much dependent on the molecular structure of the solvent. Considering these phenomena to be caused by the shift of the following chemical equilibria : CoCl_2X_2+(n-2)X=CoX_n^2++2Cl^-, CoBr_2X_2+(n-2)X=CoX_n^2++2Br^-, where X represents a solvent molecule and n is 4 or 6, the author has discussed the existence of the above equilibria at normal pressure and concluded that the equilibrium constants are much dependent on the molecular structure of the solvent. In primary alcohols, the values of ΔV have the same order of magnitude (-200～-400cc/mole) as those expected from a dielectric consideration and increase rapidly with the increase of the pressure, whereas in secondary alcohols they are large and do not change with the variations of the pressure. The author interprets these tendencies as due to the particular solvation to the Co^2+ ion by the alcohol molecules