Inorganic-organic nanocomposite materials based on macrocyclic compounds

The synthesis, structural characterisation, properties and applications of inorganic-organic hybrid materials (nanocomposites) containing macrocycles are reviewed. Three different ways to prepare such materials are discussed: i) intercalation in layered host solids, ii) entrapping into inorganic matrices generated by sol-gel, and iii) grafting of macrocycles on inorganic surfaces. Macrocyclic compounds, as crown ethers and cryptands, were the guest organic species used in intercalation processes. The host inorganic solids were layered silicates, vanadium pentoxide xerogel, transition-metal dichalcogenides and phosphorus trichalcogenides. The resulting nanocomposites present synergic host-guest properties useful for applications as solid electrolytes, ion-selective membranes and electrochemical sensors. Alternatively, nanocomposites based on macrocycles can be obtained by entrapping of such compounds into inorganic matrices generated by sol-gel, using different organosilanes as precursors (TMOS, TEOS, ETEOS, MAPTMS, etc). Electrodes based on such systems are sensitive to alkaline cations, lead, silver and ammonium ions giving linear potentiometric responses in a wide concentration range. Finally, the grafting of macrocycles on inorganic surfaces is also discussed. Silica can be functionalised by anchorage of macrocycles able to confer specific properties and reactivity to the inorganic substrate. The main applications of this last class of nanocomposites have been found for chromatography purposes, including separation of cations, anions and non-electrolytic organic compounds