Syntheses And Properties Of Metal-Organic Frameworks Based On 5-(6-Carboxynaphthalen-2-yl)Isophtahalic Acid Ligand

In this paper, we designed and synthesized a new unsymmetrical tricarboxylic acid ligand (5-(6-carboxynaphthalen-2-yl)isophtahalic acid, H3L) successfully. Seven metal-organic frameworks (MOFs) have been solvothermally synthesized with transition metal salts, main group metal salts, lanthanide metal salts and characterized by single crystal X-ray diffraction, powder X-ray diffraction, TGA, FTIR, elemental analysis. In addition, luminescent properties and gas adsorption of the MOFs were investigated.1. Based on (5-(6-carboxynaphthalen-2-yl)isophtahalic acid, three transition metal MOFs were synthesized:[Cd3L2(H2O)3]-6DMF (1), [Cd3L2(H2O)4]-3DMA (2), [ZnL]·(CH3)2NH2+·DMF (3).1-3 featured a three-dimensional (3D) (3,6)-connected net with Schlafli symbol of (45.64.86)(43)2, (612.83)(63)2 and (4.62)2(42.610.83), respectively. Furthermore, the luminescent properties of 1-3 were investigated, they were blue-shift obviously compared to the ligand.2. Based on (5-(6-carboxynaphthalen-2-yl)isophtahalic acid, one main group metal MOF was synthesized:[PbL]·H3O+·DMA (4). A single-crystal X-ray diffraction analysis revealed that 4 crystallizes in the monoclinic space group P21/c with 3D supramolecular frameworks. Thermogravimetric analysis showed that 4 is the most stable of the four MOFs. Besides, the fluorescent properties of compound 4 was studied, the results show that it was red-shift obviously compared to the ligand.3. Based on (5-(6-carboxynaphthalen-2-yl)isophtahalic acid, three lanthanide organic frameworks were synthesized:[LnL(H2O)2]·DMF·H2O (Ln= Eu (5), Tb (6), and Ho (7)). A single-crystal X-ray diffraction analysis revealed that these three MOFs are isostructural except the lanthanide ions used, displaying a 3D network with (3,6)-connected flu-type topology. The compounds exhibited selective adsorption toward CO2 over CH4 at ambient temperature, and different luminescent response to small molecules.