Syntheses,Structures And Properties Of Zinc/Cobalt Metal-Organic Frameworks

Metal–organic frameworks（MOFs）,as a new class of hybrid porous materials,have attracted much attention over the past two decades.They have many potential applications in various domains,such as chemical sensing,drug delivery,bioimaging,gas storage and separation,luminescence,heterogeneous catalysis and magnetism.In recent years,fluorescent MOFs have special research significance and become promising new sensing materials due to the synergistic function of permanent porosity and luminescence characteristic.The luminescent properties of MOFs are mainly dependent on their structures,the coordination environments of the metal centers and the characteristics of the pore surfaces,etc.Many controllable factors affect the structural assembly process of these materials,such as organic ligands,synthetic methods,reaction temperature,pH and the solvent system.Among these factors,organic ligand plays a vital role in the construction of novel architectures and functionalities.Most of the organic ligands are multicarboxylic acids,which have been proven to be good choices to prepare luminescent MOFs by a large number of literatures.In recent years,organic ligands of tetrazolium carboxylic acids have received special attention,owing to their strong coordination ability and high structural stability.In this paper,in order to explore more diversities of structure and property,we chose a semi-rigid V-shaped multicarboxylate ligand 2-4（-carboxyphenoxy）terephthalic acid（H₃cpta）,rigid ligand 5-（4-（tetrazol-5-yl）phenyl）isophthalic acid（H₃tzpa）and semi-rigid ligand 5-（4-（1H-tetrazol-5-yl）benzyl）oxy)isophthalic acid（H₃L）as organic linkers to react with Zn（Ⅱ）and Co（Ⅱ）to synthesize six new MOFs under solvothermal/hydrothermal conditions.Chemical sensing and electrochemical properties of these new MOFs were also studied.The main research results of this paper are as follows:1.By using H₃cpta as the main ligand,4,4’-bipyridyl（4,4’-bipy）as an auxiliary ligand and Zn（Ⅱ）ion as metal center,two three-dimensional（3D）MOFs,{[Zn₂（μ₃-OH）（cpta）（4,4’-bipy）]·H₂O}_n（1）,{[Zn₃（μ₂-OH）（Hcpta）（cpta）（4,4’-bipy）]·1.5H₂O}_n（2）were synthesized under hydrothermal/solvothermal conditions.1 exhibits a 3D（2,3,10）-connected framework with the extended point symbol of{4·6}²{4¹²·6¹²·8⁴}.2 is a 3D structure containing two-dimensional（2D）layers,which are further pillared by 4,4’-bipy ligands to complete the structure.At room temperature,1 and 2 exhibit good chemical sensing to Cr³⁺,Cr₂O₇^2-ions and p-nitrophenol（p-NP）.2.By using H₃tzpa ligand and Zn（Ⅱ）/Co（Ⅱ）ions,two 3D MOFs,{[Zn₂（tzpa）（phen）（μ₂-OH）]·H₂O}_n（3）and{[Co₂（tzpa）（μ₃-OH）（H₂O）₂]·4H₂O}_n（4）,were synthesized.In 3,2D layers are interdigitated in a staggered···ABAB···fashion,and then form 3D frameworks linked by H-bonds andπ-πinteractions.4 exhibits a 3D framework,which can be rationalized as a（6,6）-connected 2-nodal net with a unique{4¹¹·6⁴}topology.The experimental results indicated that 3 has good selectivity in detection of metal ions and aromatic nitro explosives,and can be used in the development of fluorescent probes.The experimental results show that 4 exhibits good electrocatalytic performance in the oxygen evolution reaction（OER）,offering a low a stable current density of 10 mA·cm^-2 at 520 mV in base media.3.By using H₃L as the main ligand,with Zn（Ⅱ）/Co（Ⅱ）ions as the metal centers,two 3D MOFs,{[Zn₂（μ₃-OH）（L）（H₂O）₂]·2H₂O}_n（5）and{[Co₂（μ₃-OH）（L）（H₂O）₂]·H₂O}_n（6）,were synthesized.The structure of 1 and 2 can be described as a（5,5）-connected net with a point symbol of{4⁶·6⁴}which belongs to classic boron nitride（bnn）topology topology.At room temperature,5 exhibits good chemical sensing to Hg²⁺and Cr₂O₇^2-ions,which can be used for the development of fluorescent probe.6 can be used as a electrocatalyst for oxygen evolution reaction.