Syntheses and Properties of Coordination Polymers with Mixed Halides or Sulfur-Containing Bifunctional Ligands

基於混鹵素或含硫雙官能團配體的配位聚合物的合成與性質

Student thesis: Doctoral Thesis

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Award date2 Sep 2019

Abstract

Coordination polymers (CPs) with organic and inorganic components have attracted broad attention due to the potential applications in diverse aspects such as gas adsorption, luminescence, catalysis, drug delivery etc. In construction of CPs, choosing and designing ligands is a key step, and the mixed ligands or ligands with mixed functional groups are crucial for achieving novel structures and enhanced functions in practice. This thesis presents the development of novel CPs with mixed halides or sulfur-containing bifunctional ligands, including synthesis of a two-dimensional bismuth mixed-halide anion, synthesis of two dithiolcarboxylate-silver polymers, and an efficient methodology in preparing carboxyl-thiol ligands for constructing zirconium based metal-organic frameworks.

Firstly, a brief introduction of CPs’ structures with regards to ligand types is provided and the features and research status of applying mixed-halides strategy and bifunctional ligands in construction of CPs are highlighted. Applications of CPs are also briefly summarized.

The effect of mixing halides is presented in constructing a series of novel bismuth-halide CPs, namely (TMP)[BiI5] (1), (TMP)[BiBr5] (2), (TMP)[BiCl5] (3) and (TMP)1.5[Bi2I7Cl2] (4), with the same organic ammonium N,N,N’,N’-Tetramethylpiperazine (TMP2+) templates. Compounds 1-3 have one-dimensional bismuth-halide connectivity; while two-dimensional bismuth-halide connectivity for the mixed-halogen compound 4. The optical band gap, electrical conductivity, photoconductivity response and high stability indicate compound 4 a potential light-harvesting material.

A bifunctional ligand with dithiolcarboxylate group is designed and used in the construction of CPs targeting narrow band gap semiconductors. Two silver-CPs, [Ag(BSL1)]n (5, BSL1 = pyridine-4-dithiocarboxylate) and [Ag2(BSL1)(BSL1S)]n (6, BSL1S = pyridine-4-perthiocarboxylate) were isolated. For 5, the pyridine N atoms coordinate to the Ag+ center and forms a two-dimensional square framework; while for 6, such Ag-N bonds do not exist and only one-dimensional structure forms. Interestingly, this difference leads to the distinct absorption properties in NIR region. Under 800 nm radiation 5 features strong photothermal effect.

A new strategy for the synthesis of carboxyl-thiol ligands and an efficient strategy for the corresponding CPs were developed. Utilizing nucleophilic substitution between benzyl thiol and aromatic halides, and AlCl3-promoted deprotection of the resultant benzyl thioether, we succeeded in attaching the thiol groups onto the carboxylate linker backbones in a dense array. The widened access of thiol-equipped MOFs facilitates in-depth exploration of open framework sulfur chemistry, achieving, for instance, fast removal of Hg with facile crosslinking.

Base on the strategy for synthesizing carboxyl-thiol ligands and their zirconium MOFs, three new carboxyl-thiol ligands and the corresponding zirconium MOFs were synthesized. These new MOFs show layered structure and have free standing thiol groups in high density. The frameworks can be modified using some soft metal ions and exhibit obvious change in light response and electric response.