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

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.