Aggregation of Cobalt (II) Tetrasulfonated Phthalocyanine in Methanol- Water Solutions

Abstract : Metal complexes of tetrasulfonated phthalocyanine (TSPC) are of interest as oxidation and hydrolysis catalysts for thioethers and organophosphonates. Since metal TSPC complexes aggregate in aqueous solution, it was necessary to determine the dimerization constant as a prerequisite to establishing the efficiency of the monomeric TSPC complexes as catalysts. Since these complexes will be used in mixed solvents to dissolve thioethers, the aggregation of the Cobalt (II) TSPC (CoTSPC) was measured in methanol-water solutions at various temperatures. The dimerization constant was determined by a nonlinear least-squares fit of absorbance versus concentration of CoTSPC. Values of the molar absorption coefficients for the monomer and dimer at 662 nm are 9.6 + or - 100,000/M and 7.5 + or - 80,000/M/cm, respectively, with the error representing the standard deviation of four solutions measured at five-degree intervals over the range 15-45 C. The dimerization of CoTSPC in the presence of methanol was measured over the same temperature range with methanol percent mole fraction from 0.4 to 9.8. The temperature dependence of the free energy of dimerization in methanol-water was expressed as delta F = A + BT + CT sq. indicating that the heat capacity of dimerization was linearly dependent on temperature. In pure water the heat capacity of dimerization was zero.