Ligand substitution equilibrium in the macrocyclic molybdenum(V) complex

The thermodynamics of the reaction of tetraphenylporphyrin(oxo)(hydroxo)molybdenum with imidazole (Im) in toluene was studied spectrophotometrically in a polythermal mode. It was established that the reaction of Im with O=Mo(OH)TPP includes several stages, two of which can be studied by spectrophotometrical titration. The first equilibrium stage is Im coordination to the eighth coordination site (K ₁ = 1.85 × 10³ l/mol), the second stage is the coordination of the second Im molecule with the displacement of OH^? into the outer sphere (K ₂ = 4.80 × 10² l/mol). The enthalpy and entropy contributions to the stability constant of tetrapheny lporphyrin molybdenum(V) complexes with Im were determined.