The enthalpy changes associated with the solution of 5,10,15,20-tetrakis(1′-methylpyrid-4- and 3-yl)porphine tetratosylates in aqueous solutions of magnesium acetate and copper(II) acetate were determined using a calorimetric method with spectrophotometric control at 298.15 K. The enthalpies of protonation of these porphyrins in an aqueous HCl solution were also estimated. In copper(II) acetate solutions, the porphyrin was found to rapidly coordinate with the copper cation. The electronic effects of the tetrapyridyl fragments, differing by heteroatom positions (para- and meta-), were found to influence the enthalpy of the coordination reaction of these ligands with Cu2+ ions. The results indicate that the nature of the porphyrin anion (iodide or tosylate) and the isomerism of the pyridyl substituent significantly affect the thermochemical characteristics of the compound solutions. Specifically, porphyrin-tosylates exhibited substantially better solvation compared to their iodide analogues. This paper presents new experimental data on the thermostability of selected cationic N-methyl-pyridylporphyrins in both inert and oxidizing media. It also examines the influence of porphyrin molecular structure on the thermal degradation onset temperature.
