Volumetric properties of tetraphenylporphine, their metallo-complexes and some substituted tetraphenylporphines in benzene solution

Densities, apparent molar volumes and partial molar volumes of benzene solutions of tetraphenylporphine, H2TPP, tetraphenylporphine metallo-complexes, MTPP (where M = Ni,Cu,Zn,Pd,Ag, and Cd) and some substituted tetraphenylporphines H2T(i-R)PP (where i = 2-4 and R = -Cl,-CH3, -OCH3), H2T(i-F)PP (where i = 2,3), H2T(3-Br)PP, and H2T(3-I)PP were determined at 25 degrees C. It was found that the partial molar volumes of the studied compounds correlate linearly with the first ionization potential of the corresponding metal atom. The calculated values of the surface and volume accessible to the solvent, and the solvent-excluded volume for different conformations of H2TPP, were compared with experimental data. The volume per molecule for different crystalline forms of H2TPP and MTPP were compared with the partial molar volumes of the corresponding compounds in benzene solutions. The correlation between the partial molar volumes of H2T(3-R)PP and their Van der Waals volumes are presented for R = -H, -F, -CH3, -Cl, -Br, -OCH3, and -I. The experimental data are rationalized in terms of differences in the conformational states of the molecules.