Construction And Property Of Metal-Organic Frameworks Based On Tripodal Ligands With Relative Low Symmetry

Metal-organic frameworks (MOFs) have been extensively studied in recent years due to their structural diversity, novel topology and potential application in gas storage and separation, catalysis, magnetism and luminescent materials. However, the ability to predict and control the structure of MOFs is seriously restricted by the bewildering structure influencing factors, such as inbeing of metal centers, the nature of predesigned organic ligands, reaction conditions and so on. A variety of MOFs with novel structures and interesting properties have been synthesized by using the rational design of organic ligands and the selection of metal centers. Although there are a large number of MOFs reported to now, there is not a mature theory to guide it. In order to realize the goal, it is necessary to accumulate more experience and experimental data.Organic ligands and metal centers are the main factors determining the MOFs’structures and properties. In this thesis,18 new MOFs were synthesized based on four tripodal ligands with relative low symmetry, namely biphenyl-3,4’,5-tricarboxylic acid (H3L1), [1,1’:3’,1"-terphenyl]-4,4",5’-tricarboxylic acid (H3L2), pyridine-3,5-bis(phenyl-4-carboxylic acid) (H2L3),3,5-di(pyridine-4-yl)benzoic acid (HL4). The influence of metal centers, the auxiliary ligands and reaction conditions on the structures and properties of the complexes were investigated. There are four parts in this thesis:1. Reactions of H3L1 and H3L2 with lanthanide series salts gave five new lanthanide-organic frameworks{[Ln(L1)(H2O)(DMF)]·DMF·H2O}n [Ln=La (1), Ce (2), Sm(3)] and {[Ln(L2)(H2O)2]·2DMF·14H2O}n [Ln=Sm (4), Gd (5)] (DMF=N, N-dimethylformamide). 1-3 and 4-5 are isostructural, respectively. There are binuclear paddlewheel [Ln2(CO2)4] clusters as the secondary building units (SBUs), which are linked by organic ligands to form three-dimensional (3D) frameworks with three different kinds of channels. In addition, thermal stability and the photoluminescence property of 1-5 were studied.2. Seven new MOFs with formula{[Zn(L3)]·2.6H2O}n (6), [Cd(L3)(H2O)(DMA)]n (7), [Co3(L3)2(HCOO)2(H2O)2]n (8),{[Mn(L3)(H2O)]DMF}n (9),{[Er4(L3)3(n3-OH)4 (H2O)4]·(NO3)2-7H2O·10DMF}n (10),{[Ln4(L3)3(μ3-OH)4(H2O)4]·(NO3)2-7H2O·7DMF}n [Ln =Yb (11), Lu (12)] (DMA=N, N-dimethylacetamide) have been synthesized by solvothermal reactions of H2L3 with the corresponding metal salts. They have novel structures and topologies. There are five different coordination modes of (L3)2". The results show that the metal centers with different coordination number and geometry have crucial role in determining the structure of MOFs. Among them,10-12 are isostructural with rare {63.109.123}{6}3 topology. Photoluminescence, magnetic and sorption properties were investigated. Selective and hysteretic sorption of CO2 over N2 was found for 10-12.3. Four new MOFs{[Zn(L4)(HCOO)(H2O)]·H2O}n (13),{Cd(L4)2}n (14), {Co(L4)(BDC)0.5(H2O)}n (15) and {[Co2(L4)2(BDC)(H2O)]·4DMF·8H2O}n (16) [H2BDC= 1,4-benzenedicarboxylic acid] were synthesized.13 is a two-dimensional (2D) network, which is further assembled into 3D supramolecular architecture through hydrogen bonding interactions.14 is a 2-fold interpenetrating 3D framework, while 15 is a 3D net formed by interpenetration of 2D bilayers (2D+2Dâ†'3D). Selective and hysteretic sorption of CO2 was found for 15 at 195 K. Hysteretic sorption of N2 was found at 77 K and selective sorption of CO2 was found at 195 K for 16. Additionally, photoluminescence and catalytic property were investigated.4. New MOF{[Zn3(L2)2(DABCO)(H2O)]·9DMF}n (17) has been synthesized by using H3L2 and 1,4-diazabicyclo[2.2.2]octane (DABCO), which is isostructural to the previously reported complex{[Cu3(L2)2(DABCO)(H2O)]·15H2O·9DMF}n (18). The transition metal ions (Zn2+ and Cu+) in the paddle-wheel SBUs with coordinated water molecules could be exchanged by each other to form hybrid bimetallic MOFs via a direct single-crystal to single-crystal transformation. The results show that the adsorption and photoluminescence properties have been improved significantly. The post-synthesis method can be used to synthesize the isostructural MOFs that can not be obtained by direct synthesis.