Comparative solvolytic stabilities of copper(II) nanoballs and dinuclear Cu(II) paddle wheel units

The self-assembly of copper(II) ions and 5-(2-(2-hydroxyethoxy)ethoxy)benzene-1,3-dicarboxylic acid (2) leads to hollow nanoballs in which 12 dinuclear copper(II) paddle wheel units are interconnected via 24 ligands, as determined by single crystal X-ray structure analysis. The nanoball dissociates in aqueous solutions, and in the presence of an excess of ligand it transforms into a three-dimensional network, but is stable in organic solvents. The thermodynamic stability of the nanoball against dissociation in aqueous solution is studied and compared to simple copper(II) paddle wheel complexes. The results reveal enhanced thermodynamic stability of the nanoball as compared to discrete copper(II) paddle wheel complexes due to chelate effects and positive cooperativity.