Octahedral cobalt(III) complexes in dipolar aprotic solvents. VI. Spectrophotometric determination of ion association of halide ions with cis-chlorodimethylformamidebisethylenediaminecobalt(III) ion and cis-chlorobromobisethylenediaminecobalt(III)ion in anhydrous NN-dimethylformamide

Abstract

Using a spectrophotometric technique the ion association constants for three systems of octahedral cobalt complexes and halide ions have been determined at three temperatures in NN-dimethylformamide. The values of K, ΔHº, and ΔSº for each system have been calculated. At 30º they are as follows: cis-[CoCl(DMF) en₂]²⁺ + Cl^- ↔ ion pair K=1.51±0.03 x 10⁴ 1.mole^-1(ΔH⁰= 0.93 ± 0.02 kcal mole^-1,ΔSº= 22.l+0.4 e.u) cis-[CoCl(DMF) en₂]²⁺+2Cl- ↔ ion triplet K= 1.21±0.05 X 10⁶ 1.² mole^-2(ΔHº=-3.8±0.lkcal mole^-1, ΔSº=15.41± 0.5 e.u) cis-[CoCl(DMF) en₂]²⁺+Br^- ↔ ion pair K= 9.20±0.18 X 10³ 1.¹ mole^-1(ΔHº=-7.2±0.lkcal mole^-1, ΔSº=42± 1.0 e.u) cis-[CoBrCl en₂]⁺ + Br^- ↔ ion pair K = 690±l41. mole^-1 (ΔHº = 1.27±0.03 kcal mole^-1, ΔSº= 8.8±0.2 e.u.) The dependence of the measured K, the association constant, on the wavelength of measurement, small amounts of water in the solvent, and the anion of the complex salt, has also been investigated.