Formation of mixed ligand complexes of cobalt(II) with chloride and substituted pyridines in 1,2-dichloroethane

Abstract

Equilibria of a series of complexes of type CoCl 2(R-Py) 2 (where R-Py=2-methyl-(2Me-Py), 3-methyl-(3Me-Py), 4-methyl-(4Me-Py), 4-acetyl-(4ac-Py) and 4-cyanopyridine(4CN-Py), and pyridine(py)) with TBA·Cl (tetrabutylammonium chloride) in 1,2-dichloroethane have been investigated spectrophotometrically. In the presence of excess R-Py, dichloro complex gives rise to a following configurational equilibrium: CoCl 2(RPy) 2+2RPy ⇋ CoCl2(RPy) 4 (tetrahedral) (octahedral) The substitution equilibria of the tetrahedral complexes are written as: CoCl 2(RPy) 2+TBA·Cl ⇋ K 3 (TBA)CoCl 3(RPy)+RPy (TBA)CoCl 3(RPy)+ TBA·Cl ⇋ K 4 (TBA) 2CoCl 4+RPy Stepwise formation constants, log K 3, were determined as 3.48, 3.70 and 4.10 ± 0.03 for 4Me-Py, 3Me-Py and Py, respectively. The constants, log K 4, for 4Me-Py, 3Me-Py, 2Me-Py, Py, rac-Py and 4CN-Py are 0.08, 0.27, 1.18. 0.48, 1.06 and 1.59 ± 0.01, respectively. The constants, log K 3 and log K 4, show linear correlations with the basicity or R-Py, p K b , except for the 2Me-Py complex. Visible and near infrared spectra of the tetrahedral complexes are presented.