Molecular Recognition of Aromatics in Spherical Nanocages.

Abstract

In general, due to the lack of efficient specific molecular interactions, achieving host-guest molecular recognition inside large and neutral metal organic cages (MOCs) is challenging. Preferential molecular recognition of aromatics using the internal binding sites of interlocked icosahedral (i.e., spherical) M12L8MOCs within poly-[n]-catenane (1) is reported. The guest absorption has been monitored directly in the solid-state by consecutive single-crystal-to-single-crystal (SCSC) reactions in a gas-solid environment, using single-crystal X-ray diffraction (SC-XRD) experiments. The preferential guest uptake is corroborated by Density Functional Theory (DFT) calculations by determining the host-guest interaction energy (Ehost-guest) with the nitrobenzene (NB) >> p-xylene (p-xy) >> o-dichlorobenzene (o-DCB) trend (i.e., from 44 kcal/mol to 25 kcal/mol), assessing the XRD outcomes. Combining SC-XRD, DFT and solid-state 13C NMR, the exceptional stability of the M12L8 cages, together with the guest exchange/release properties are rationalized by the presence of mechanical bonds (efficient π-π interactions) and by the pyridine's rotor-like behaviour (with 3 kcal/mol rotational energy barrier). The structure-function properties of M12L8 makes 1 a potential candidate in the field of molecular sensors.