Octakis(Carboxyalkyl-Thioethyl)Silsesquioxanes and Derived Metal Complexes: Synthesis, Characterization and Catalytic Activity Assessments

Two octakis(carboxyalkyl-thioalkyl)silsesquioxanes (COOH-PSx) were obtained by click photo-induced thiol-ene addition reactions between octavinyl-T8-silsesquioxane and thioalkylcarboxylic acids. Their structures were confirmed by elemental and spectral analyses and in one case by single-crystal X-ray diffraction. The natrium salts of COOH-PSx were used as very efficient ligands for Cu, Ni and Cd ions. The formation of transition metals complexes was confirmed by FT-IR spectroscopy, showing the coordination pattern, and by EDX semiquantitative elemental analysis. They were analyzed in terms of thermal stability, morphology and moisture sorption. The catalytic activity was tested in alkaline decomposition of hydrogen peroxide, the copper complexes showing the best activity, that is 40% conversion after ~ 40 min. A copper complex was also efficient as catalyst in photodecomposition of Congo Red under UV light, without additional oxidation agents or pH adjustments, showing discoloration efficiency of ca. 89% after 145 min and recycling ability. Thus, the results indicated the compounds reported here, obtained by simple and reproducible synthetic protocols, as efficient, stable and re-usable heterogeneous catalyst. The possibilities of structural diversification (by the nature of the functional groups and the metal ion) are wide and of the application potential.