Porous Molecular Crystals by Macrocyclic Coordination Supramolecules

摘要

In this study, we show how the combination of metal ions, counter-anions and opportunely functionalized and preorganized ligands gives rise to two distinct supramolecular isomers, coordination polymeric chains and hexameric macro-cycles. The hexamers then aggregate to form a cubic structure exhibiting permanent microporosity. The supramolecular assemblies are formed with Ag~+, thioether functionalized bis(pirazolyl)methane ligands and CF_3SO_3~-/PF_6~- as the counter-anions. Five different ligands were prepared by modifying the peripheral thioether moiety with naphthyl, methoxy, m-Me, p-Me and F groups (L~(SNf), L~(SPhOMe), L~(SPhm-Me), L~(SPhp-Me), and L~(SPhF)). Helicoidal coordination polymeric chains are formed with CF_3SO_3~- (general formula [Ag(L)]_n(CF_3SO_3)_n), whereas macrocyclic hexamers are formed with PF_6~- (general formula [Ag(L)]_6(PF_6)_6). The macrocycles self-assemble into ordered capsules with the shape of a tetrahedron, and the overall framework is sustained by Ag~+...(PF_6~-)...Ag~+ contacts. The capsules generate a highly symmetric structural arrangement, which is characterized by permanent microporosity arising from two distinct types of microporous chambers in the structure. The gas absorption isotherms show that the materials can selectively adsorb CO_2 and N_2O over CH_4 and N_2. The modulation of the microporosity of the materials is achieved by the different thioether functionalization of the ligands L~(SNf), L~(SPhOMe), L~(SPhm-Me), and L~(SPhF). The diffusion and localization of the gas molecules within the cavities were investigated by 2D ~1H-~(13)C solid state NMR on samples loaded with enriched ~(13)CO_2, showing that both types of cavities are accessible to guest molecules from the gas phase.