Supramolecular Aggregation in Organic Solvents of Discrete Copper Complexes Formed with Organosiloxane Ligands

Three complexes of copper with organosiloxane ligands of bis-azomethine type derived from 1,3-bis(3-aminopropyl) tetramethyldisiloxane and 2-hydroxybenzaldehyde (1), 5-nitro-2-hydroxybenzaldehyde (2), and 3,5-di-tert-butyl-2-hydroxybenzaldehyde (3) having well-established structures were investigated for their ability to form aggregates in organic solvents, namely dimethylformamide. The thermal behavior in solid state was investigated by thermogravimetrical analysis (TGA) and differential scanning calorimetry (DSC), the results being correlated with the structure and intermolecular interactions highlighted by crystallographic analysis. The co-existence in these structures of nonpolar 1,3-bis(propyl) tetramethyldisiloxane moiety and a polar one, consisting in metal complexed through hydroxy-azomethine groups, makes them able to self-assemble both in solid state and in solution. The surface activity of the complexes was evaluated by surface tension measurements, whereas the formation of the aggregates in solution was emphasized by UV-Vis spectroscoppy, dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS) analyses. The DSC curves recorded in solution revealed the presence of large endotherms in the range 30-100 degrees C, which prove the presence of the aggregates. The preservation of these assemblies after solvent evaporation was studied by transmission electron microscopy (TEM) and atomic force microscopy (AFM).