Metal-Organic Framework-Based Selective Molecular Recognition of Organic Amines and Fixation of CO2 into Cyclic Carbonates

Synthesis and structural depiction of two new metal-organic frameworks (MOFs), namely, [{Zn(L)(oba)}center dot 4H(2)O](alpha) (Zn-MOF-1) and [{Cd-1/2(L)(1/2)(nipa)(1/2)(H2O)(1/2)}center dot(DMF)(1/2)(H2O)](alpha) (Cd-MOF-2) (where L = N-2,N-6-di(pyridin-4-yl)naphthalene-2,6-dicarboxamide, 4,4'-H(2)oba = 4,4'-oxybisbenzoic acid, and 5-H(2)nipa = 5-nitroisophthalic acid) are reported. Both Zn-MOF-1 and Cd-MOF-2 have been prepared by reacting ligand L and coligand 4,4'-H(2)oba or 5-H(2)nipa with the respective dihydrates of Zn(OAc)(2) and Cd(OAc)(2) (OAc = acetate). Crystal structure X-ray analysis discloses that Zn-MOF-1 displays an overall 2D -> 3D interpenetrated framework structure. The topological analysis by ToposPro suggests a (4)-connected uninodal sql topology with a point symbol of {4(4).6(2)} having 2D + 2D parallel polycatenation. However, crystal packing of Cd-MOF-2 adapted a porous framework architecture and was topologically simplified as (3,4)-connected binodal 2D net. In addition, both Zn-MOF-1 and Cd-MOF-2 were proved to be multifunctional materials for the recognition of organic amines and in the fixation of CO2 to cyclic carbonates. Remarkably, Zn-MOF-1 and Cd-MOF-2 showed very good fluorescence stability in aqueous media and have shown 98 and 97% quenching efficiencies, respectively, for 4-aminobenzoic acid (4-ABA), among all of the researched amines. The mechanistic study of organic amines recognition proposed that fluorescence quenching happened mainly through hydrogen-bonding and pi-pi stacking interactions. Additionally, cycloaddition of CO2 to epoxide in the presence of Zn-MOF-1 and Cd-MOF-2 afforded up to 96% of cyclic carbonate within 24 h. Both Zn-MOF-1 and Cd-MOF-2 exhibited recyclability for up to five cycles without noticing an appreciable loss in their sensing or catalytic efficiency.