Volumetric properties of tetraphenylporphyrin, octaethylporphyrin, and their metallo complexes in organic solvents

Densities, apparent molar volumes, and partial molar volumes were determine d for (a) tetraphenylporphyrin, H2TPP, and ZnTPP in several organic solvent s and (b) H2TPP, octaethylporphyrin, H2OEP, and the metallo complexes MTPP and MOEP (where M = Zn, Cu, Ni, Pd. Cd, Ag) in benzene and chloroform solut ions at 25 degreesC. The effect of solute-solvent interactions on molecular packing was followed by examining changes in the ratios of van der Waals v olumes to the partial molar volumes of solute and solvent. Using this metho d. the volumetric properties of H2TPP were compared with those of the macro molecules 18-crown-6-ether, cryptand-222, and C60. For benzene solutions of MOEP metallo complexes, the linear dependence between the partial molar vo lumes and the half-wave oxidation potentials was determined. It was found t hat the partial molar volumes of MTPP in the chloroform solution correlate linearly with the distance between the metal atom and the nitrogen atom of the pyrrole moiety of the metallo complex.