Thermodynamics of porphyrin sublimation

The saturated vapor pressures of tetraphenylporphyrin H2TPP, its four-coord inated metallo-complexes MTPP (M = Ni, Cu, Zn, Pd, Ag, Cd) and some phenyl- substituted derivatives H2T(R)PP (R = 2-, 3-, 4-CH3; 2-, 4-F; 2-, 3-, 4-Cl; 3-, 4-Br; 3,5-C(CH3)(3)) have been measured using the inert gas flow metho d. The values of sublimation enthalpy Delta H-sub(m) and entropy Delta S-su b(m) are calculated. On the basis of the kinetic vapor pressure dependence, the start temperatures of thermal destruction of the investigated porphyri ns are determined. The temperatures of melting of the tetraphenylporphyrin metallo-complexes measured by the DSC method are in linear correlation with the Delta H-sub(m) values. The correlation between the thermodynamic funct ions of porphyrin sublimation (Delta H-sub(m), Delta S-sub(m), Delta (sub)G (m)) and the literature data on the crystal structure of the compounds is c onsidered. The Delta H-sub(m) values obtained by some authors by different methods are compared with the results of our investigations. Possible reaso ns for discrepancies in the results are discussed. Copyright (C) 2000 John Wiley & Sons, Ltd.