Titration calorimetric investigation of interactions of zinc(II), nickel(II), and copper(II) tetraphenylporphine complexes with pyridine in three solvents

Titration calorimetry was used in a thermodynamic study on the interactions of pyridine (Py) with zinc(II)-tetraphenylporphine (ZnTPP), nickel(II)-tetraphenylporphine (NiTPP), and copper(II)-tetraphenylporphine (CuTPP) in benzene, chloroform, and carbon tetrachloride solutions. The coordinating properties of the metalloporphyrins in relation to pyridine were found to diminish in the order ZnTPP > CuTPP > NiTPP. Solvation effects were estimated from the interactions between metalloporphyrins (MP) and Py. The more negative values of the enthalpy and entropy of reaction of ZnTPP with Py, following the order of solvents CCl4 > C6H6 > CHCl3, was found to be related to the different types of (MP-solvent) and (Py-solvent) interactions. The NiTPP and CuTPP complexes showed the opposite trend.