Reversible binuclear Cu(II) complex formation in a new sonogel-cryptand hybrid material

New hybrid materials are obtained by embedding Cu(II) complexes of the open-chain triethylenetetraamine ligand (tren) or a related binucleating cryptand containing two tren subunits in sonogel matrixes prepared from tetraethoxysilane (TEOS) or methyltriethoxysilane (MTEOS). The effectiveness of trapping depends on both the matrix and the nature of the complex. The chemical behavior and textural parameters of the different samples are explained according to a textural model with three different types of sites for trapping. The most promising samples for sensing purposes are TEOS-based silica sonogel matrixes containing the binuclear Cu(II) cryptate, where reversible reactions with small ions (H+-, Cu2+, N3(-)) take place in a way similar to that observed in solution. However, successive reaction cycles lead to the partial loss of the trapped cryptand. Leaching becomes less important when the sonogel is prepared from TEOS and a salt of the protonated cryptand. In this case, the texture of the matrix is more suitable for cryptand trapping, and treatment with solutions containing Cu2+, N-3(-), or H+ leads to a larger number of reversible complex formation-decomposition processes.