The majority of MOFs have been constructed by using rather simple di and tri carboxylic acids as linkers. Whereas, highly connected linkers (containing more than four carboxylic acid groups) can produce stable frameworks with a wider range of topological constructs. In the past, our group has reported a series of 3D MOFs developed from tetrakis(p-carboxyphenyl) silane (TCPS) linker, hexakis(4-carboxyphenyl)disiloxane, and methyl-substituted tetracarboxylic acid siloxane as linkers. Expanding the scope of this work, a series of di, tri, tetra, hexa, and octapodal derivatives of carboxyphenyl silane compounds containing additional amide functionality were synthesized. The tetrapodal linker (L1) was further extended to two amide groups per arm, to increase the arm length of the linker to obtain materials with larger pores. All synthesized linkers were purified, recrystallized, and characterized through NMR spectroscopy, IR spectroscopy, single crystal x-ray diffraction analysis, and mass spectrometry. The crystal structure analysis of tetrapodal linkers (L1, with one amide group per arm and L4, two amide groups per arm) revealed the presence of intermolecular hydrogen bonding between nitrogen atoms of the amide group and hydroxyl groups of carboxylic acid functionality, making them two-dimensional hydrogen-bonded sheets. These linkers were reacted with various metal salts under solvothermal conditions in attempts to obtain novel metal-organic frameworks decorated with amide functional groups, with potential affinity and high selectivity for carbon dioxide gas.

Amide functionalized organosilicon polycarboxylic acid linkers for metal-organic frameworks

ACS Fall 2021

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