Pressure Effects on the Complexes of Cobalt(ll) Chloride in Acetone Solution

Abstract

The effects of pressure on the visible absorption spectra of the complexes of cobalt(II) chloride in acetone solution were studied up to 8000kg/cm2 at room temperature by using a high pressure optical vessel with sapphire windows.
The following two kinds of equilibria are found to coexist:
CoC12(Ac)2 + 4Ac ↔ Co(Ac)62+ + 2Cl-(1)
CoC12(Ac)2 + Cl-↔ CoCl8(Ac)- + Ac(2)
where Ac denotes an acetone molecule. The former is an equilibrium between the species which have four and six coordination. The latter is an equilibrium between the species with different ligands, Which has not been observed in any kind of alcohol solution.
As log K1 exhibited curvature against pressure, quadratic functionality (6), which is most common now in use, and equation(7), Hamann's equation newly proposed, were applied to the relation. Both ef the results are shown in Fig. 3.
Since equilibrium (1) forms ions, ΔV1 is large negativevalue as expected from ion-solvent interaction. Also ΔV1 has rather large pressure dependence as listed in Table 1. While equilibrium (2) is scarcely affected by pressure.