Temperature dependence study of five-coordinate complex formation of zinc(II) octaethyl and tetraphenylporphyrin

Five coordinate complex formation of zinc(II)–octaethylporphyrin (Zn(OEP)) and zinc(II)–tetraphenylporphyrin (Zn(TPP)) have been studied in the presence of seven systematically selected electron donor molecules. Stability constants in toluene were determined at various temperature ranged between 20 and 60°C by absorption and steady-state fluorescent measurements from which thermodynamic parameters were determined. Depending on the porphyrin and the axial ligand the entropy is changing between −127 and −61 J mol−1 K−1 while the enthalpy is ranging from −49 to −24 kJ mol−1.