Inorganic Chemistry, Vol.56, No.4, 2188-2197, 2017
Water-Stable In(III)-Based Metal-Organic Frameworks with Rod-Shaped Secondary Building Units: Single-Crystal to Single-Crystal Transformation and Selective Sorption of C2H2 over CO2 and CH4
Three new water-stable In(III)-based metalorganic frameworks, namely, [In-3(TTTA)(2)(OH)(3)(H2O)]center dot(DMA)3 (BUT-70, DMA = N,N-dimethylacetamide), [In-3(TTTA)(2)(CH3O)(3)] (BUT-70A), and [In-3(TTTA)(2)(OH)(3)] (BUT-70B), with rod-shaped secondary building units (SBUs) and an new acrylate-based ligand, (2E,2'E,2 '' E)-3,3',3 ''-(2,4,6-trimethylbenzene-1,3,5-triyl)-triacrylate (TTTA(3)) were obtained and structurally characterized. BUT-70A and -70B were generated in a single-crystal to single-crystal transformation fashion from BUT-70 through guest exchange followed by their removal. The solvents used for guest exchange were methanol and dichloromethane, respectively. Single-crystal structure analyses show that the guest exchange and removal process is accompanied by the substitution of coordinated water molecules of In(III) centers with uncoordinated carboxylate O atoms of TTTA(3) ligands. Moreover, hydroxyl groups bridging two In(III) centers are also replaced by methoxyl groups in the transformation from BUT-70 to -70A. Overall, three metalorganic frameworks (MOFs) are constructed by infinite chains consisting of corner-sharing InO4(OR)(2) (R = H or Me) octahedral entities, which are interconnected by TTTA(3) ligands to form three-dimensional frameworks. Unlike most reported MOFs with infinite chains as SBUs, such as well-known MIL-53 and M-MOF-74, which have one-dimensional channels along the chain direction, the BUT-70 series contain two-dimensional intersecting channels. The BrunauerEmmettTeller surface area and pore volume of BUT-70A were estimated to be 460 m(2) g(1) and 0.18 cm(3) g(1), respectively, which are obviously lower than those of BUT-70B (695 m(2) g(1) and 0.29 cm(3) g(1)). Gas adsorption experiments demonstrated that BUT-70A and -70B are able to selectively adsorb C2H2 over CO2 and CH4. At 1 atm and 298 K, BUT-70A uptakes 3.1 mmol g(1) C2H2, which is 3.6 times that of the CO2 uptake and 7.2 times that of the CH4 uptake. Compared with BUT-70A, BUT-70B presents an even higher C2H2 uptake of 3.9 mmol g1 at the same conditions, but slightly lower Ideal Adsorbed Solution Theory C2H2/CO2 and C2H2/CH4 selectivities.