Thermophysical and structural properties of crystalline solvates of tetraphenylporphyrin and their zinc, copper and cadmium metallo-complexes

Abstract

The results of a thermochemical and structural investigation of the process of desolvation of crystalline solvates of tetraphenylporphyrin H 2TPP with o-, m-xylene; zinc(II) tetraphenylporphyrin ZnTPP with benzene, toluene, o-, m-, p-xylene; cadmium(II) tetraphenylporphyrin CdTPP and copper(II) tetraphenylporphyrin CuTPP with o-, m-xylene are reported. Thermogravimetry and differential scanning calorimetry were used to determine the stoichiometry of crystalline solvates, the energy of activation and the heat effect of the desolvation process. The lattice parameters of the unsolvated crystalline CdTPP, ZnTPP and crystalline solvates of ZnTPP with p-xylene and CuTPP with m-xylene were determined using the X-ray powder diffraction method and the algorithm of Ito. The stoichiometry 1:1 for crystalline solvates [ZnTPP+( p-xylene) 1] and [CuTPP+( m-xylene) 1] was observed. The values of free volume per solvent molecules V free defined as the difference between volume of unit cell of crystalline solvate and the sum of the volume of a unit cell of unsolvated phase of an investigated compound and Van der Waals volume of solvent molecules were calculated. The packing coefficients K chan of the solvent molecules located in channels of the porphyrin matrix were also calculated. For ZnTPP crystalline solvates, we found the correlations between heat of desolvation and free volume per guest molecules of unit cell, as well as between the coefficient of channel packing and the temperature for which the half-lifetime of desolvation phase is equal to 60 min. A linear kinetic compensation effect for the crystalline solvates studied was found.