Increase in pore size and gas uptake capacity in indium-organic framework materials

We herein report the synthesis and characterization of a new charged metal-organic framework, [Et2NH2]-[In(BPTC)] (InOF-2) (InOF = indium-organic framework; BPTC = biphenyl-3,3',5,5'-tetracarboxylate), featuring an unc-type topology. Interestingly, InOF-2 undergoes a distinct porosity transition on going from a typical reversible type-I N-2 isotherm to a type-IV N-2 isotherm with a hysteresis loop when employing thermal treatment. A Li+-exchanged material [Li-0.9(H3O)(0.1)][In(BPTC)] (InOF-2-Li+) is obtained using an ion-exchange method with BET surface areas estimated to be 1494 m(2) g(-1), and 867 m(2) g(-1) for InOF-2, indicating that the N-2 adsorption capacity of InOF-2-Li+ significantly increases by ca. 72.3%. Meanwhile, H-2 adsorption measurements show a corresponding improvement in H-2 storage capacity (ca. 70.6%) on going from InOF-2 (1.14 wt%) to desolvated InOF-2-Li+ (1.95 wt%) at 1.0 bar and 77 K, which is comparable to the calculated increase in BET surface area. A similar improvement is also confirmed in other single gas adsorption measurements, including CH4 and CO2. Overall, the performance characteristics of InOF-2 and InOF-2-Li+ indicate these two materials to be unprecedented examples for the charged metal-organic frameworks to improve their gas storage capacity with both the thermal treatment and cation-exchange method, showing promise for more applications in producing more porous metal-organic frameworks.