SYNTHESIS, STRUCTURAL STUDIES AND APPLICATION OF CARBOXYLIC ACID BASED SUPRAMOLECULES

Abstract

Supramolecular chemistry can be considered as a modern day approach to design and synthesize new solids materials with desired physical and chemical properties. A metal organic framework is one of the significant classes of supramolecular chemistry which deals the synthesis of multifunctional materials with tuneable properties. For the exploration of possible structural diversity, semi-flexible/flexible carboxylic acid based ligand was used as building block because of the following reasons:- These ligands contains –CH2- group between two aromatic rings that can provide a subtle conformation adaptation. Presence of two or more carboxylic groups in the ligand offers suitable number of oxygen atoms which can easily satisfy the coordination number of metal centre. These ligands contains highly conjugated system and mainly responsible for fluorescent property. Apart from these, these ligands are novel and reported first time in this work for the generation of novel metal organic frameworks. The first chapter of thesis is the general introduction and presents an up to date survey of literature related to the synthesis of various rigid/flexible/semi-flexible ligands and their metal organic frameworks with metal ions. The different types of metal organic frameworks related to the present research have been posed in the context of the cited work. The second chapter of thesis deals with the synthesis of two novel three dimensional metal organic frameworks (MOFs) based on 5,5′,5″-(2,4,6-trimethyl-1,3,5-pheneylene)tris(methylene)tris(azanediyl)triisophthalic acid (H6L) ligand, {[Zn4(L)1/3(H2O)4]6+ [S]}n (2a) and {[NaCd2(L)(DMF)3]-·(Me2NH2+)(3DMF)}n (2b), where S in 2a is a squeezed solvent molecule, DMF = dimethylformamide, under solvothermal conditions. MOF- 2a is a three dimensional porous metal organic framework containing paddle wheel binuclear [Zn2(COO)4 and Zn2(COO)3] secondary building units (SBUs). Topological analysis shows that the whole network can be viewed as a (3, 3, 3, 4)-connected four nodal net with point symbol of {3.16^2}5{3^3.16^2.17} which is a novel topological type. MOF-2b is a three dimensional intrapenetrating metal organic frameworks with Cd2Na trinuclear secondary building units (SBUs). Topological study shows that the whole network can be viewed as a (3, 4, 5, 10)-connected four nodal net with point symbol of {3.4.5^2.6^2} {3.4^4.5^3.6^2} {3.4^8.5^5.6^24.7^5.8^2} {4^3} which is a novel topological type. Thermal study reveals that both MOFs are stable upto 350 oC. In photoluminscent spectrum, the emission peak of free ligand (H6L) appeared at 430 nm (λex = 340 nm), which can be attributed to π* → n or π* → π transitions while emission peaks in emission spectra of 2a and 2b were obtained at 450 nm (λex ii = 365 nm) and 443 nm (λex = 365 nm), respectively. Moreover, the enhancement of emission peaks was also observed in comparison of free ligand, which makes them more suitable for photochemical applications. The sensing results showed that both MOFs act as selective sensor towards phenolic nitro explosive [nitrophenol (NP), dinitrophenol (DNP) and trinitrophenol (TNP)]. Furthermore, 2b showed the selective adsorption of CO2 while N2 molecules adsorbed only on surface and typically behave like ultramicroporous material. By contrast, 2a showed selectivity towards N2 molecules at 77K. The third chapter of thesis deals with the synthesis of two novel three dimensional metal organic frameworks (MOFs) based on 4,4',4''-(((2,4,6-trimethylbenzene-1,3,5-triyl)tris(methylene))tris(azanediyl))tribenzoic acid (H3L) ligand, {[Zn4(L)2(NO3)(H2O)3] (NO3)}n (3a) and {[Cd4(L)2(NO3)(DMF)8(H2O)](NO3)(DMF)2}n (3b) where DMF = dimethylformamide, under solvothermal conditions. MOF- 3a is a twofold interpenetrating three dimensional porous metal organic framework containing paddle wheel binuclear [Zn2(COO)3] secondary building units (SBUs). Topological analysis is shows that the whole network can be viewed as a (3, 4, 6)-connected three nodal net with point symbol of {3.16^2}5{3^3.16^2.17} which is a novel topological type. MOF- 3b is also a twofold interpenetrating three dimensional porous metal organic framework containing paddle wheel binuclear [Cd2(COO)3] secondary building units (SBUs) but both interpenetrating frameworks are parallel to each other. Topological analysis shows that the whole network can be viewed as a (3, 6)-connected two nodal net with point symbol of {4^3.6^12}{4^3}2 which is assigned to a novel topological type. Thermal study reveals that both MOFs are stable upto 430 oC. Comparison of gas adsorption behavior shows that both MOFs (3a & 3b) are microporous in nature and showed selectivity toward CO2 over N2 gas at 273K. The fourth chapter of thesis deals with the synthesis of novel semi flexible ligand 9,10-bis((4-carboxylato-pyridinil)methyl)anthracene (cpma) which is further used with chloride/ nitrate salts of transition metals ions [Cu(II), Zn(II), Cd(II)] to form three new coordination polymers (CPs) (4a – 4c) with 2D, 1D and 0D frameworks by solvothermal technique. CP- 4a is 2D chain. Each completely deprotonated cpma ligand coordinated with Cu(II) metal centre in two different coordination modes:- μ4-η1:η1:η1:η1 and μ4-η1:η0:η1:η1. Topological study shows that the whole network can be viewed as a (3, 3)-connected two nodal net with point symbol of {3.4.5}2{3} which is a novel topological type. CP- 4b is a 1D chain. The Zn(II) metal is four coordinated and has a distorated tetragonal [ZnO2Cl2] environment comprising of two carboxylate O atoms of two cpma moieties and two chloride ions. In CP-4b, the cpma moiety acts a μ-linker with its two COO− groups acting in monodentate mode. The μ-cpma linkers iii multiply interconnect to adjacent Zn(II) centers to generate a 1D chain structure. The completely deprotonated cpma ligand coordinates to two Zn(II) ions in a μ4-η1:η0:η1:η0 coordination mode. Topological study showed that such chains are composed of the 2-connected Zn nodes and the μ-cpma linkers and are classified as a uninodal 2-connected net. The CP-4c coordination polymer has a discrete dimeric structure. Single crystal X-ray structural analysis showed that asymmetric unit of 4c consists of one Cd(II), one completely deprotonated ligand cpma, one bromide anion and one nitrate anion. The μ-cpma moiety acts as a μ linker via one bidentate and one monodentate COO- groups and overall ligand act as tridentate ligand. The completely deprotonated L ligand coordinates to two Cd(II) cations in a μ4-η1:η0:η1:η1 coordination mode. Further, the appropriate particle size of all CPs was calculated by the PXRD pattern using Debye−Scherrer equation and found that all the CPs are of nano range. Upon incubation of these fluorescent nano CPs with the HCT-15 cell line, the MTT assay has revealed least toxicity of all nano CPs even at highest concentration of 25 μM observed for 24 hours, indicating a high degree of biocompatibility of these nano CPs. These nano CPs were evaluated in live-cell imaging assays using HCT-15 as a model cell-line and showed that CP- 4b has richest fluorescence potential. The fifth chapter of thesis deals with the synthesis of a series of lanthanide based metal organic frameworks {[Ln(cpma)3/2(H2O)2]·(NO3)2} {cpma = 9,10-bis((4-carboxylato-pyridinil)methyl)anthracene) (Ln = Y, La, Nd, Sm, Eu, Gd, Tb and Dy) from novel semi-flexible ligand (cpma), under solvothermal conditions. All these are isostructural, three dimensional (3D) porous metal organic framework with one dimensional channel and form (4, 4, 6)-connected, three nodal net with new topology. {[Sm(cpma)3/2(H2O)2]·(NO3)2} (5d) was selected as a representative example for nitro explosive sensing and adsorption studies. Thermal study reveals that MOF – 5d is stable up to 450 oC. Solid state emission study showed that enhancement of emission peaks in 5d, in comparison of free ligand, makes them more suitable for photochemical applications. Fluorescence sensing results suggested that MOF – 5d act as selective sensor for picric acid out of other nitro aromatics. Furthermore, Comparison of gas adsorption study shows that MOF- 5d is highly selective towards CO2 gas than other gases (N2 and CH4 ) at 273K. The sixth chapter of thesis deals with the reaction of novel semi flexible ligand 9,10-bis((4-carboxylato-pyridinil)methyl)anthracene (cpma) with chloride salts of lanthanides to forms 1D/ 3D MOFs (6a – 6h) by solvothermal technique. 6a – 6c are 3D MOFs have {[Ln(cpma)(H2O)2]·Cl3}n general formula and (3,8) connectivity with 2 nodel net which is a novel topology. 6d – 6f are 1D MOFs have {[Ln(cpma)2(H2O)4]·Cl3·DMF·EtOH·(H2O)3}n iv general formula and (2, 4) connectivity with 2 nodel net. 6g, 6h have {[Ln(cpma)(H2O)4]·Cl3}n general formula and (4, 4) connectivity with 2 nodel net which is also a novel topology. TGA analysis show that all the MOFs show regular weight loss with temperature due to presence of large voids having with large number of solvents and stable upto 350 oC. We have also calculated the approximate size of the all 1D MOFs (6d – 6f) from Debye Scherer formula which show that these MOFs have particle size in nano range (lesser than 100 nm) and these MOFs have highly fluorescent behavior which is suitable for biological applications. Upon incubation of these fluorescent nano MOFs with the HCT-15 cell line, the MTT assay has revealed least toxicity of all nano MOFs even at highest concentration of 25 μM observed for 24 hours, indicating a high degree of biocompatibility. The confocal fluorescence and brightfield images of HCT-15 cells were determined by laser scanning confocal microscopy is green channel. The MOFs 6d and 6f have shown fluorescence and also confirmed the membrane-permeable property while MOF 6e does not found to have fluorescence activity due to lower fluorescence property in comparison to 6d and 6f. The materials and the reagents, synthetic procedure, experimental details and different type of spectroscopic measurements for all the compounds including the ligands and MOFs reported in chapter 2-6 have been provided in seven chapter of the thesis.