Mutual effects of equatorial and axial ligands on the stability of praseodymium(III) and samarium(III) phthalocyanine complexes

Abstract

The nature of axial ligand in lanthanide(III) phthalocyanine complexes markedly affects their physicochemical properties. The role of axially coordinated anion in the stability of coordination sphere was determined by the example of praseodymium(III) and samarium(III) phthalocyanine complexes (X)LnPc (X = Cl–, Br–, AcO–). The synthesis and the results of dissociation kinetics study of the complexes under the action of AcOH in ethanol solution were presented. Stability parameters for the complexes, kinetic equations, and activation parameters for the dissociation of coordination centers were determined. Effect of the axial ligand on the strength of macrocycle binding and the stoichiometric mechanism of complex dissociation reaction was considered. The state of axial bond in the complexes was shown to determine the value of reaction order toward acid (1 or 2) and the nature of rate-limiting step of the reaction: with participation of molecule or ionized in the axial direction complex.