Two Robust Porous Metal-Organic Frameworks Sustained by Distinct Catenation: Selective Gas Sorption and Singile-Crystal-to-Single-Crystal Guest Exchange

Assembly of copper(1) halide with a new tripodal ligand, benzene-1,3,5-triyl triisonicotinate (BTTP4), afforded two porous metal-organic frameworks, [Cu2I7(BTTP4)]superset of 2CH(3)CN (1.2CH(3)CN) and [CuBr-(BTTP4)superset of(CH3CN center dot CHCl3 center dot H2O) (2.solvents), which have been characterized by IR spectroscopy, thermogravimetry (TG), single-crystal, and powder X-ray diffraction (PXRD) methods. Compound 1 is a polycatenated 3D framework that consists of 2D (6,3) networks through inclined catenation, whereas 2 is a doubly interpenetrated 3D framework possessing the ThSi2-type (ths) (10,3)-b topology. Both frameworks contain 1D channels of effective sizes 9 x 1.2 and 10 x10 angstrom(2), which amounts to 43 and 40% space volume accessible for solvent molecules, respectively. The TG and variable-temperature PXRD studies indicated that the frameworks can be completely evacuated while retaining the permanent porosity, which was further verified by measurement of the desolvated complex [Cu2I2(BTTP4)] (1'). The subsequent guest-exchange study on the solvent-free framework revealed that various solvent molecules can be adsorbed through a single-crystal-to-single-crystal manner, thus giving rise to the guest-captured structures [Cu2I2 (BTTP4)superset of C6H6 (1.benzene), [Cu2I2 (BTTP4)superset of 2C(7)H(8) (1.2 toluene), and [Cu2I2(BTTP4)]superset of 2C(8)H(10) (1.2 ethylbenzene). The gas-adsorption investigation disclosed that two kinds of frameworks exhibited comparable CO2 storage capacity (86-111 mLg(-1) at 1 atm) but nearly none for N-2 and H-2, thereby implying its separation ability of CO2 over N-2 and H-2. The vapor-adsorption study revealed the preferential inclusion of aromatic guests over nonaromatic solvents by the empty framework, which is indicative of selectivity toward benzene over cyclohexane.