Thermodynamics and kinetics of the formation of the supramolecular complexes bisacetato(5,10,15,20-tetraphenylporphinate)zirconium(IV) with pyridine and imidazole

The equilibria and rates of step reactions for the formation of the supramolecular complexes of bisacetato(5,10,15,20-tetraphenylporphinate)zirconium(IV) (AcO)₂ZrTPP and bioactive bases pyridine (Py) and imidazole (Im) in toluene were studied using UV-Vis and IR spectroscopy. The step stoichiometric mechanism, including the reversible coordination of two Py molecules (K ₁ = 1.8 × 10⁸ l²/mol²), the equilibrium of the displacement of two AcO⁻ into the second coordination sphere by increasing the concentration of the solvent polar component (K ₂ = 2.4), and the coordination of the third and fourth Py molecules in a one step with the formation of [(Py)₄ZrTPP]²⁺ · 2(AcO)⁻ (K ₃ = 2.8 × 10⁴ l²/mol²), was verified. It was established that the spectrophotometric titration is sensible for the two-stage π-π-complexation of [(Py)₄ZrTPP]²⁺ · 2(AcO)⁻ with Py molecules (K ₄ = 29 l/mol and K ₅ = 1.8 l/mol). It was shown that the stronger base Im reacts irreversibly with (AcO)₂ZrTPP. The thermodynamic and optical characteristics of (AcO)₂ZrTPP required for using the complex in the detection of bioactive bases were studied.