Discrete cyclic supramolecules and nanotubes self-assembled to form porous materials. (Invited oral presentation)

Coordination-driven self-assembly of metals and properly designed molecular linkers can lead to the formation of discrete supramolecules of specific geometrical shapes, which can in turn self-assemble into complex crystalline architectures enabling the fabrication of porous materials. We reported the formation of cyclic hexameric structures of Ag(I) or Cu(I) coordinated with multipodal bis(pyrazolyl)methane moiety. The anions play a crucial role in the arrangement of the cyclic hexamers forming two families of permanently porous 3D crystalline structures, that are able to reversibly entrap vapors and gases. The crystalline structures contain cavities with Platonic solid geometries, which can absorb reversibly CO2 and CH4. The localization of the gas molecules within the cavities was investigated by 2D 1H−13C solid state NMR on samples loaded with enriched 13CO2, showing that the cavities are accessible to guest molecules from the gas phase. Moreover, we prepared new 1D metal–organic frameworks formed by the packing of discrete metal-organic nanotubes through weak hydrophobic interactions. The self-assembly process leads to the formation of microcrystals and nanorods depending on the synthesis conditions. The CO2 absorption kinetics drastically increased from the micrometric crystals to the nanorods, highlighting the effects of the particle sizes. We have recently discovered an innovative property of porous materials: the intrinsic dynamics for the presence of fast molecular rotors in their structure with correlation times on the nanosecond scale. Solid state NMR played an important role for the determination of motional trajectories of chemical groups in the frameworks. We achieved the systematic regulation of the rotor speed by the absorption of chemical species such as I2, opening perspectives in responsive materials. Ref. J. Am. Chem. Soc. 2014,136,14883; J. Am. Chem. Soc. 2012,134, 9142; J. Am. Chem. Soc. 2014,136,618.