The composition and structure of Fe(TAPPI)], where H2(TAPPI) = tetrakis(p-trimethylammoniophenyl)porphyrin, were established by elemental anal., magnetic susceptibility measurement, and IR and UV spectrometry. The pH titration curves indicated that there is an equilibrium between the monomer and dimer of Fe(TAPPI) in the aqueous solution at different pH values. The polymerisation nos. and dimerization equilibrium constants at constant ionic ionic strength and the thermodn. parameter of polymerisation reaction were obtained from spectrophotometric pH titration curves. The equilibrium constants of reaction between Fe(TAPPI) dimer and different axial ligands (imidazole, 1-methylimidazole, L-histidine and pyridine) and their thermodn. parameters in H2O and H2O-dioxane mixed solvent were determine by spectrophotometry. The thermodn. parameters are discussed.

Key words: PORPHINE P, THERMODYNAMIC PROPERTIES, COMPLEX COMPOUNDS, TRIMETHYLALKYLAMMONIUM, IODIDE, EQUILIBRIUM CONSTANT, POLYMERIZATION