Thermodynamics of formation of molecular synthetic metalloporphyrin complexes with pyridine in benzene and in chloroform at 298.15 K

Microcalorimetric titration was used to determine the thermodynamic charact eristics (K-C, DeltaH, and DeltaS) for the axial coordination of pyridine b y the metal complexes of synthetic porphyrins (ZnTBP, ZnTPTBP, MgTPTBP, and CuTPTBP) in benzene and in chloroform at 298.15 K. The capability of the m etalloporphyrins under study to coordinate pyridine in chloroform decreases as follows: ZnTPP > ZnTBP > ZnTPTBP > MgTPTBP > CuTPTBP. The complicated c ourse of the studied processes was shown to be determined by the electronic structure of the central metal atom, the nature of the porphyrin macrocycl e, and by the specific solvation interactions of metalloporphyrin and pyrid ine with the solvent molecules.