Syntheses, Structures and Sorption Properties of Three Isoreticular Trinuclear Indium-Based Amide-Functionalized...

Amide-functionalized metal-organic frameworks (AFMOFs) as a subclass of MOF materials have received great interest recently because of their intriguing structures and diverse potential applications. In this work, solvothermal reactions between indium nitrate and two mixed-linkers afforded two new isoreticular 8-connected trinuclear indium-based AFMOFs of [(In₃ O)(OH)(L2)₂ (IN)₂ ]⋅(solv)_x (2-In) and [(In₃ O)(OH)(L2)₂ (AIN)₂ ]⋅(solv)_x (NH₂ -2-In) (H₂ L2=4,4'-(carbonylimino)dibenzoic acid and HIN=isonicotinic acid or HAIN=3-aminoisonicotinic acid), respectively. Moreover, by means of reticular chemistry, an extended network of [(In₃ O)(OH)(L3)₂ (PB)₂ ]⋅(solv)_x (3-In) (H₂ L3=4,4'-(terephthaloylbis(azanediyl))dibenzoic acid, HPB=4-(4-pyridyl)benzoic acid) was also successfully realized after prolongation of the former dicarboxylate linker and HIN, resulting in a truly 8-connected isoreticular AFMOF platform. These frameworks were structurally determined by single-crystal X-ray diffraction (SCXRD). Sorption studies further demonstrate that 2-In and NH₂ -2-In exhibit not only high surface areas and pore volumes but also relatively high carbon capture capabilities (the CO₂ uptakes reach 60.0 and 75.5 cm³  g^-1 at 298 K and 760 torr, respectively) due to the presences of amide and/or amine functional groups. The selectivity of CO₂ /N₂ and CO₂ /CH₄ calculated by IAST are 10.18 and 12.43, 4.20 and 4.23 for 2-In and NH₂ -2-In, respectively, which were additionally evaluated by mixed-gases dynamic breakthrough experiments. In addition, high-pressure gas sorption measurements show that both materials could take up moderate amounts of natural gas.