SYNTHESIS AND STRUCTURAL STUDIES OF METAL ORGANIC FRAMEWORK USING SULFONATES AS A BUILDING BLOCK

Abstract

The metal-organic framework can be seen as a modern approach in designing and synthesizing new solid materials with the desired physical and chemical properties. In the metal-organic framework, a component with a proton donor and an acceptor may exhibit a range of non-covalent interactions. In the context, sulfonic acid is an essential ligand for the formation of diverse supramolecular architectures. For the sake of convenience, the work represented in the thesis has been divided into the following chapters: The first chapter of the thesis includes the brief introduction and literature survey regarding the metal-organic framework having sulfonates and different N–heterocyclic ligands showing the properties of gas adsorption, proton conductivity and sensing of nitroaromatic compounds. In the second chapter of the thesis, various zinc and cadmium containing metal-organic frameworks viz., [Zn·AHP·1,5-NDS·DMF] (2a), [Zn·AHP·4-SBA(DMA)2] (2b), [Zn·AHP·3-SBA] (2c), [Cd(AHP)21,5-NDS(DMF)2] (2d), [Cd·AHP·1,5-NDS] (2e),[Cd·AHP·2,6-NDS·DMF(H2O)2] (2f), [Cd·AHP·SIA(H2O)2] (2g) and [Cd·AHP·SSA(DMF)2H2O] (2h) using the semi-rigid 1,1′-(anthracene-9,10 diylbis(methylene))bis(pyridin-1-ium-4-olate) ligand (L = AHP) and various sulfonic acid analogs [1,5-naphthalenedisulfonic acid (1,5-NDS), 3-sulfobenzoic acid (3-SBA), 4 sulfobenzoic acid (4-SBA), 5-sulfosalicylic acid (SSA), 5-sulfoisophthalic acid (SIA) and 2,6-naphthalenedisulfonic acid (2,6-NDS)] have been synthesized by a hydrothermal method. They have been characterized by powder X-ray diffraction thermogravimetric analysis and single-crystal X-ray diffraction methods. The X-ray studies showed that 2b, 2d, and 2h have two-dimensional architectures, whereas 2a, 2c, 2e, 2fand 2g have three-dimensional structures. The topological analysis demonstrated that all the zinc-containing MOFs have a hexagonal (hcb) net topology with the point symbol of the framework being {63} whereas cadmium-containing 2d has an sql net topology with the point symbol of the framework being {44·62} and 2e has a hcb net topology with the point symbol of the framework being {63}. Since all synthesized MOFs have fluorescence properties, they have been used as imaging agents for MCF7 cells. The cytotoxic experiments show that more than 92% of cells survive at the dose 100 μg ml−1. The cell imaging results show that the MOF particles were found in the cytoplasm rather than in the nucleus and these can be used further as a conjugate with any known anti-cancer drugs in cellular distribution. The emission properties of these MOFs have been utilized for the detection of an herbicide (simazine) as well as nitroaromatic compounds. The quenching constant for PA (picric acid) in 2g was found to be 5.01 × 104 M−1, which may be due to the interaction of picric acid and co-ligands present in 2g. semi-rigid The third chapter of thesis deals with solvothermal reaction of cobalt nitrate/copper nitrate with 1,1'-(anthracene-9,10-diylbis(methylene))bis(pyridin-1-ium-4-olate) (L=AHP) ligand and disulfonates [(1,5-naphthalenedisulfonic acid (1,5-NDS)/2,6 naphthalenedisulfonic acid (2,6-NDS)] resulted in the formation Co(II)/Cu(II) containing metal-organic framework namely [Cu2(AHP)2(H2O)2(1,5-NDS)] (3a), [Cu.AHP(H2O)0.5(2,6 NDS)0.5] (3b), [Co.AHP.1,5-NDS] (3c), [Co(AHP)2.5DMA(1,5-NDS)2(DMA)(H2O)3] (3d) and [Co(AHP)3(2,6-NDS)] (3e). These MOFs have been structurally characterized by different methods, including single-crystal X-ray diffraction. The structural analysis revealed that the number of coordinated AHP ligand is different in different MOFs and each coordinated AHP ligand is actively involved in the formation of one dimensional chain. Also, the presence of 1,5-NDS/2,6-NDS, either in coordinated or free form (lattice) plays an important role in increasing the dimensionality of the frameworks. The characterized MOFs have been tested for their proton conductivity property and dye degradation ability. The presence of free water and 1, 5-NDS in the cavity of 3d encouraged us to perform the proton conductivity measurement for this MOF. 3d seems to maintain its framework structure in a variety of humid environments and ensures smooth conduction pathways mediated by water molecules. Depending on the temperature and humidity levels, this MOF performed moderate to high proton conductivity (6.96x10-4 to 1.95x10-3 S cm-1). Out of these MOFs, only 3a shows the degradation of methylene blue (about 82%) in the presence of hydrogen peroxide (H2O2). The increase of degradation activity in the presence of H2O2 indicated the formation of hydroxyl radical in the reaction process. The fourth chapter of the thesis deals with the synthesis of 9,10-bis[(1H-imidazol-1 yl)methyl] anthracene(BIA) ligand. The synthesized BIA ligand was used for the formation of MOFs using different metal salts, viz., MnCl2.4H2O, Co(NO3)2·6H2O, Cu(NO3)2·3H2O and different sulfonic acids (1,5-naphthalenedisulfonic (1,5-NDS) and 5-sulfoisophthalic acid (SIA)). The hydrothermal reaction of above components resulted in the formation of four novel metal-organic frameworks namely, [Cu.BIA.1,5-NDS.DMF] (4a), [Mn(BIA)0.5(1,5 NDS)0.5DMA] (4b), [Co(BIA)1.5(SIA)2DMF.EtOH] (4c) and [Co.BIA.1,5-NDS.DMA] (4d), where DMF denotes dimethylformamide. These metal coordination polymers were characterized by elemental analysis, thermo-gravimetric analysis and single-crystal X-ray iv diffraction technique. Suitable crystals of 4a-4d for single crystal X-ray measurements were grown in mixed solvents (DMF/DMA and MeOH/EtOH). TGA analysis revealed that all the MOFs show regular weight loss with temperature due to the presence of large voids having a large number of solvents and stable upto 350 oC. We have also calculated the approximate size of all MOFs (4a-4d) from the Debye Scherer formula, which shows that these MOFs have a particle size in the nano range (lesser than 90 nm) and these MOFs have highly fluorescent behavior which is suitable for biological applications. Further, when HeLa cells were incubated with MOFs and observed under an inverted microscope, most of them exhibited green colored fluorescence. Upon merging both bright field and fluorescent images, the MOFs were found to be scattered in the cytoplasm rather than in the nucleus. The fifth chapter of the thesis deals with the synthesis of flexible methylene bis(pyrazole) (MBPz) and sulfonates ligand i.e. 5-sulphoisothalic acid (SIA), 3-Sulfobenzoic acid (3-SBA), 4-Sulfobenzoic acid (4-SBA) and 2,6-Naphthalenedisulfonic acid (2,6-NDS). By using these ligands, five new metal-organic frameworks, namely [Cu.SIA.MBPZ(H2O)2] (5a), [Ni(2,6 NDS)0.5MBPZ.(H2O)3] (5b), [Cd.2,6-NDS(MBPZ)2] (5c), [Cd2.4-SBA(MBPZ)2] (5d) and [Cd.3-SBA(MBPZ)2] (5e) have been synthesized. The crystal structure analysis revealed that the use of different sulfonic acid resulted in the different architectures ranging from one dimensional to a three-dimensional supramolecular structure. Hirshfeld surface analysis plot reveals the intermolecular interaction in which sulfonates participates with itself, with other organic molecules and also solvent molecule in the crystal structure suggested that the hirshfeld dnorm surface of sulfonates mainly covered by O···H/H···O, C···H/H···C and H···H interaction. A thermal study suggested that both MOFs are stable upto 530 oC. The adsorption isotherm of N2 for 5c and 5d at 77K shows typical type I behavior. Compared with the N2 adsorption, 5c and 5d showed limited CO2 uptakes at 1 bar and 298 K. The materials and the reagents, synthetic procedure, experimental details and different types of spectroscopic measurements for all the compounds, including the ligands and MOFs reported in chapter 2-5, have been provided in the sixth chapter of the thesis.