Water-Stable In(III)-Based Metal-Organic Frameworks with Rod-Shaped Secondary Building Units: Single-Crystal to Single-Crystal Transformation and Selective Sorption of CH over CO and CH.

Three new water-stable In(III)-based metal-organic frameworks, namely, [In(TTTA)(OH)(HO)]·(DMA) (BUT-70, DMA = N,N-dimethylacetamide), [In(TTTA)(CHO)] (BUT-70A), and [In(TTTA)(OH)] (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) 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 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 metal-organic frameworks (MOFs) are constructed by infinite chains consisting of corner-sharing InO(OR) (R = H or Me) octahedral entities, which are interconnected by TTTA 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 Brunauer-Emmett-Teller surface area and pore volume of BUT-70A were estimated to be 460 m g and 0.18 cm g, respectively, which are obviously lower than those of BUT-70B (695 m g and 0.29 cm g). Gas adsorption experiments demonstrated that BUT-70A and -70B are able to selectively adsorb CH over CO and CH. At 1 atm and 298 K, BUT-70A uptakes 3.1 mmol g CH, which is 3.6 times that of the CO uptake and 7.2 times that of the CH uptake. Compared with BUT-70A, BUT-70B presents an even higher CH uptake of 3.9 mmol g at the same conditions, but slightly lower Ideal Adsorbed Solution Theory CH/CO and CH/CH selectivities.