Supermolecular Coordination Complexes: Synthesis,radical Characters,catalytic Properties And Structural Transformation Behavior

Supramolecular coordination complexes refer to molecular antity formed from metal center and organic ligands through coordination-driven self-assembly strategy.Supramolecular coordination complexes include discrete metallacycles,supramolecular coordination cages（SCCs）and infinite metal-organic frameworks（MOFs）.The intrinsically dynamic reversibility,easy functionalization,together with the diversity species of metals,organic ligands and their topological structures of supramolecular coordination complexes endow them with unique physicochemical properties and a rich variety of functions,which make them for use as platforms in the fields of biology,chemistry,materials science,energy,medicine and so on.In recent years,the construction of functional supramolecular coordination complexes has become the research frontier and hot topic in the field of supramolecular chemistry.The main work of this thesis is to design and construct a series of metallacycles,SCCs and MOFs.Their interesting physical and chemical properties such as radical character,catalytic performance and structural transformation will be comprehensively discussed.The aim of this dissertation is to disclose the structure-properties-functions relationships of the series of supramolecular coordination complexes,and the ideas for the construction of functional supramolecular metal complexes are provided.The main contents of this thesis include the following parts:Chapter 1 This chapter mainly introduces the concept,development process,synthetic strategy and applications of supramolecular coordination complexes in different research fields.In this chapter,the classical structures and construction strategies of discrete and infinite supramolecular coordination complexes are reviewed,and the research progress in the aspects of free radical properties,catalytic properties and structural transformation of supramolecular coordination complexes are summarized.Supramolecular coordination complexes have many advantages,such as easy synthesis,easy modification and easy functionalization,and have shown good application prospects in many fields.At the end of this chapter,the research topic of this thesis is proposed to construct a series of supramolecular coordination complexes,and study their properties in the aspects of free radical,catalysis and structural transformation.Chapter 2 A series of radical supramolecular coordination complexes with different number,location and distance of TEMPO radical units were successfully constructed to fine tune the intramolecular and intermolecular spin-spin interactions.Moreover,the reversible manipulation of spin-spin interactions through external stimulation was successfully achieved in this unique radical system.First,a series of exo-and endo-TEMPO radical-functionalized metallacycles 2-11,2-12,2-13,2-14,2-14a and metal coordination cages 2-15 and 2-16 were efficiently constructed via coordination-driven self-assembly method.The structures of the compounds were throughly characterized by ¹H NMR,³¹P NMR,2D-DOSY,HR-ESI-TOF-MS and other characterization methods.In addition,the exact structures of the complexes were successfully confirmed by X-ray single crystal diffraction.CW-EPR spectroscopy was then employed to investigate the TEMPO radical properties,which is fundamental for understanding the different spin-spin interactions in 2-11 to 2-16.The 3-line EPR pattern without further splitting explicitly suggested the very weak spin-spin coupling interactions（J<<A_N）in these biradical and multiradical systems,mainly because the TEMPO units in the solution state remained in a freely dangling state with long distances from each other in these systems.Particularly,metallacycle 2-14 in the solid state exhibited a large ZFS,which was proven to be closely related to its intrinsic intermolecular spin-spin interactions.Interestingly,an unprecedented intermolecular to intramolecular spin-spin interaction switch was achieved by simple counter anion replacement;BF₄^-counterion analog 2-14a showed strong intramolecular spin-spin interactions.Moreover,the spin-spin interactions of 2-14 and 2-14a could be reversibly switched on/off by mechanical grinding and solvent vapor stimuli.To the best of our knowledge,this study represents one of very few examples of the realization of manipulating spin-spin interactions by multiple stimuli,including counterions,me-chanical force and solvent vapor.In addition,this study provides chemists with a new radical system to investigate spin-spin interactions,and the interesting findings in this work help scientists understand spin-spin interactions from a new perspective.Chapter 3 In the work of this chapter,a series of supramolecular metal coordination cages with well-defined sizes and shapes as well as different numbers of Pd ions were designed and synthesized as templates.It was found that the employment of SCCs as templates could not only significantly reduce the aggregation tendency of Pd nanoparticles but also play an important role in regulating their size and size distribution.Furthermore,the as-prepared Pd nanocatalyst could serve as highly efficient polychlorinated biphenyls（PCBs）degrader both in the stirred vessel and continuous flow reactor because of its excellent catalytic efficiency in reductive dehalogenation reaction under the mild conditions.First,through the coordination-driven self-assembly strategy,four kinds of metal coordination cages（SCCs）3-7 to 3-10 were synthesized.Second,the SCCs were successfully impregnated into the CMC support,making for four SCCs@CMC with a good SCC dispersion.Through the reduction reaction of sodium borohydride and a series of the Pd loading of Pd_n@CMC were well controlled and a series of Pd nanocatalysts were synthesized.Notably,the results of TEM were likely to confirm the close relationship between the particle size and the type of the coordination cage,the greater number of Pd ions the cage possesses,the bigger size of the metal nanocatalyst can be obtained,thus highlighting the template effects of the SCCs.Overall,the ultrasmall Pd nanocatalyst was developed in this work may represent a versatile and efficient catalyst for the reductive dehalogenation reaction and degradation of PCB,because all reactions were carried out at room temperature in good conversion,and more importantly,with a recyclable catalyst.We believe that the SCCs-templated synthesis strategy developed herein could be also applied to other high-surface-area supports,and helpful to the design of high metal loading single-site heterogeneous catalyst and even single-atom catalyst.Therefore,this strategy is expected to address the low catalyst loading issue in the preparation of large-scale size-controllable ultrasmall noble metal nanocatalysts for real industrial application.Chapter 4 In this chapter,two MOFs were successfully constructed through the self-assembly of phenazine ligands with different metals.Based on the inherent redox activity of phenazine ligands,they showed unique electrochromic performance in the redox process.The phenazine radical cation MOF showed good catalytic effect for the Diels-Alder addition reaction.Firstly,MOF 4-4 and MOF 4-6 with different structures were successfully constructed by coordination-driven self-assembly of 4,4’-（phenazine-5,10-diyl）dibenzoic acid（4-3）ligands with ZrCl₄ or Zn（NO₃）₂.X-ray powder diffraction（XRD）,thermogravimetric（TGA）,gas adsorption（BET）and other characterization methods were used to characterize the structure and properties of the MOFs.During the progress of oxidation MOF,MOF 4-4 exhibited unique electrochromic behavior.MOF 4-6 can efficiently produce free radical cation MOF 4-6-oxidation under AgSbF₆,and the conversion efficiency and stability of this radical MOF were characterized by EPR.The radical MOF showed good activity and was successfully used in the radical cation catalyzed Diels-Alder addition reactions of imines and diene compounds.In this chapter,we have successfully constructed MOFs with redox activity and studied their electrochromic behavior and the catalytic performance of free radical.This work provides a new idea for the construction of function-oriented supramolecular coordination complexes.combining the relationship of structural design and functional application.Chapter 5 In this chapter,a series of different structures of MOFs and SCCs were successfully constructed by the phenazine pyridine ligands with different metals.Supramolecular coordination complexes showed unique properties of structural transformation,further studies have been found that the interesting structural transformation was related to the different conformation of phenazine as well as the distinctly kinetic and thermodynamic stability of the assemblies.Specifically,5,10’-（pyridine-3-yl）-5,10’dihydrophenazine（5-1） was prepared to conduct coordination self-assemblies with different metals,and a series of MOFs and metal coordination cages.Interestingly,due to the syn or anti conformation of ligand 5-1,MOF 5-6exhibited an interesting structural transfromation from 1D MOF to 3D MOF 5-9.In addition,due to the planar and bent conformation of ligand in MOF 5-6.The metal coordination cages 5-10 and 5-11 also exhibited the behaviour of structural transformation.And,their mechanism of the structural transformation was systematically studied,and the mechanism of kinetically controlled 1D MOF 5-6 and thermodynamically controlled 3D MOF 5-9 was preliminarily revealed.In addition,the results showed that the mechanism of structural conversion of the metal coordination cage was also closely related to its kinetic and thermodynamic stability,and the structural transformation between the kinetically controlled metal coordination cage 5-11 and the thermodynamically controlled product 5-10 was successfully achieved through the regulation of solvent and temperature.This work elucidates the unique structural transformation phenomenon and mechanism of supramolecular coordination complexes,and provides a new idea for the study of the assembly mechanism of metal coordination and the relationship between structural transformation.In conclusion,a series of supramolecular coordination complexes,including the discrete metallacycles,SCCs and MOFs were successfully constructed in this thesis and the properties of radicals,catalysis and structural transformation were reserched,illuminating the inner relationship in the structure and property.Therefore,a series of supramolecular coordination complexes were successfully constructed in the thesis,and the properties of free radicals,catalysis and structural transformation were studied.This work enriches the supramolecular metal complex system and expands the application fields of functional supramolecular metal coordination compounds.