Development of metal-organic nanotubes exhibiting low-temperature, reversible exchange of confined "ice channels".

Nanotubular materials have unique water transport and storage properties that have the potential to advance separations, catalysis, drug delivery, and environmental remediation technologies. The development of novel hybrid materials, such as metal-organic nanotubes (MONs), is of particular interest, as these materials are amenable to structural engineering strategies and may exhibit tunable properties based upon the presence of inorganic components. A novel metal-organic nanotube, (C4H12N2)(0.5)[(UO2)(Hida)(H2ida)]·2H2O (UMON) (ida = iminodiacetate), that demonstrates the possibilities of these types of hybrid compounds has been synthesized via a supramolecular approach. Single-crystal X-ray diffraction of the compound revealed stacked macrocyclic arrays that contain highly ordered water molecules with structural similarities to the "ice channels" observed in single-walled carbon nanotubes. Nanoconfinement of the water molecules may be the cause of the unusual exchange properties observed for UMON, including selectivity to water and reversible exchange at low temperature (37 °C). Similar properties have not been reported for other inorganic or hybrid compounds and indicate the potential of MONs as advanced materials.