The thermodynamic characteristics of step complex formation in the (5,10,15,20-tetraphenylporphyrinato)(chloro)indium(III)-pyridine-toluene system

The thermodynamic characteristics, step mechanism, and spectral manifestations of step reactions between (5,10,15,20-tetraphenylporphyrinato)(chloro)indium(III) ((Cl)InTPP) and organic base pyridine (Py) in inert toluene were studied using spectrophotometric titration and physicochemical analysis of intermediate forms. The coordination of Py molecule (K (1) = 9.45 x 10(2) l/mol at 298 K) with the formation of (Cl)(Py)InTPP, the substitution of Cl- in (Cl)(Py)InTPP with the second Py molecule (K (2) = 2.3 x 10(2) l/mol), and the coordination of the third Py molecule to produce [(Py)(3) InTPP](+) center dot Cl- (K (3) = 8.7 l/mol) were observed at the first, second, and third steps, respectively. The fourth reaction stage most likely corresponds to pi-pi complex formation equilibrium between the aromatic complex and pyridine with a 1: 2 stoichiometry. The thermodynamic parameters of step reactions Delta H (a similar to) and Delta S (a similar to) well correspond to the stoichiometric mechanism of the reaction. Prospects for the use of the metalloporphyrin as a receptor of organic N-bases are considered.