A STUDY OF THERMODYNAMICS IN AXIAL COORDINATION REACTION OF UNSYMMETRICAL DERIVATIVES OF TETRAPHENYLPORPHYRINATOCOBALT(II)

-(4-Acetamidophenyl)-10,15,20-tris(4-methylphenyl) porphyrinatocobalt( II) was synthesized. BY means of spectrophotometer technique, the equi librium constants of the axial coordination reaction were measured bet ween this system and a series of imidazole ligands (2-MeIm, N-MeIm, EM Im, GMZ) which possess different steric hindrances. The results show t hat the size and the position of the substituting group on a ligand in fluence the stability of the axial coordinative product, and the equil ibrium constants appear in the order K-GMZ>KN-MeIm>K2-MeIm>K-EMIm. A l inear relationship was observed between Delta H and T Delta S in both the symmetrical and unsymmetrical systems. The favorable enthalpy chan ge compensates the unfavorable entropy change and the compensatory ent halpy-entropy relationship contributes to the stability of complexes.