Single Crystal Structure,Assembly Process And Water Oxidation Application Of Metal Clusters Of Multi-nitrogen Heterocyclic Ligands

Metal clusters have become a hot topic for chemists,biologists,and physicists as well as materials scientists because of their beautiful structure and rich variety of properties.Its synthesis is not simply a"one-pot method"to get some novel structure clusters,but to design and synthesize target clusters with specific functions.To achieve this goal,their assembly process needs to be clarified,but these assembly mechanisms are often quite complex,especially when it comes to the in-situ reaction of ligands,which is more difficult and rarely reported.Single crystal diffractometer,powder diffractometer,electrospray mass spectrometry,spectroscopic characterization and other methods were used to study the precipitation and solution in the reaction process.The precise structural information of the coordination molecule cluster was obtained by crystallography,and mass spectrometry obtained supplemental information of clusters in the solution.The use of solid-liquid structural information correlation to identify the molecular fragments in the solution reveals the assembly process of the clusters,which helps to further understand their rich and varied properties and lays a good foundation for future design of function-oriented clusters.In this paper,the authors constructed a series of multinuclear clusters based on multidentate ligands,and comprehensively studied cluster assembly process by means of single crystal diffractometry,electrospray ionization mass spectrometry,and spectral characterization.The full text is divided into three chapters:The first chapter is the preface,the research background,types,and latest developments of multinuclear metal clusters are systematically introduced.In particular,the synthesis and structural characteristics of cyclic metal clusters are introduced.In addition,the principle of electrospray ionization mass spectrometry and its application in solution coordination chemistry are introduced.The progress of high-resolution electrospray ionization mass spectrometry in studying the assembly of multinuclear metal clusters is highlighted.Finally,the advances and application prospects of the clusters in the water oxidation application are introduced,especially iron-based clusters.The basis for the construction of high-efficiency water oxidation catalysts based on iron complexes is discussed.In the second chapter,the in situ dehydration reaction of SS-H₄bzimed ligands by metal ion-induced ligands under solvothermal conditions,then successfully constructed an[Fe₃（μ₃-O）]core was surrounded by two Fe（μ-HL’）₃ units formed a novel triangular bipyramidal pentanuclear iron cluster[Fe_x^ⅡFe_5-x^Ⅲ（H₂L’）_x-1（HL’）_7-x（μ₃-O）]·（CH₃OH）₄·（H₂O）₂.At room temperature and atmospheric pressure,the mother liquor is volatilized obtained by the dinuclear iron cluster formed without the in situ dehydration reaction of the ligand.Fe₅ single crystal mass spectrometry tests show that the Fe₅ cluster can exist stably with its framework in methanol solution without additional ion source energy,which provides the necessary basis for tracking the assembly process,but when the ion source energy is increased at 40 eV and more,the framework of the Fe₅ cluster collapses.The single crystal mass spectrometry results of Fe₂ indicate that even in the absence of ion source voltage,the mass spectrum peak of Fe₂ in methanol solution is mainly the framework peak of the ligand in addition to its frame peak,which indicates that Fe₂ is far less stable than Fe₅ and it is a kinetic product.While Fe₅ is a thermodynamic product,it requires a certain temperature,time,pressure,etc.,but it is relatively stable.Although structural information of the coordination molecule clusters provided by crystallography is critical,mass spectrometry provides very important additional information for the behavior of the clusters in solution.The author used electrospray mass spectrometry,single crystal X-ray diffraction,X-ray powder diffraction PXRD,spectroscopy and other characterization methods to track the solution and precipitation of Fe₅ at different times,and explored the time and necessary species of the in situ dehydration reaction of the ligand of pentanuclear iron formation.It was found that there were[Fe₂^IIIFe^II（H₃L）₂（H₂L）₂]²⁺（m/z=633.13）after three hours of reaction.After the ligand will undergo an in-situ reaction and will gradually be assembled into Fe₅,suggesting an assembly mechanism for the formation of the Fe₅ complex.Using solid-liquid structural information correlation to identify molecular fragments in solution helps us understand the self-assembly process of multinuclear clusters,which helps to further understand their rich and varied properties and lays a good foundation for designing functionally-oriented clusters.In addition,the author explored the water oxidation application of Fe₅.The cyclic voltammograms show that the compound has rich redox potential peaks.Electrochemical measurements show that the compound can effectively and stably catalyze water oxidation.The Fe₅ pyrolyzed materials at different temperatures were characterized.In the third chapter of the thesis,the author firstly constructs Ni₄ clusters based on thiol modified triazole ligand.Four Ni²⁺planes adopt the planar tetragonal coordination configuration and are exposed on the surface of the molecular clusters.Because the Ni²⁺axial coordination is not saturated and easily attacked,the Ni₄cluster is used as the precursor in the DMF solution at room temperature and atmospheric pressure.The introduction of Cd²⁺can induce further spontaneous assembly of the Ni₄ cluster to obtain the cyclic mixed metal coordination cluster Ni_xCd_24-x.Compounds Ni_xCd_24-x can also be obtained by evaporation from the ligand and the metal salt in DMF solution system at room temperature and atmospheric pressure.Single crystal diffraction,ICP-MS and energy spectrum tests showed that n(Cd²⁺):n(Ni²⁺)=3:1 in the crystal,the average molecular formula is[Ni₆Cd₁₈（L¹）₂₃（HL¹）]·（NO₃）（C₃H₇NO）₁₂·（H₂O）₁₂.In order to understand the assembly process of N_ixCd_24-x induced by the addition of Cd²⁺,the author first studied the single crystal mass spectrometry of Ni₄ crystals.Because of the induction of Cd²⁺,Ni₄ must be broken first in order to further assemble and form a high multinuclear metal clusters.To study the single crystal mass spectrum under the condition of external energy of Ni₄ crystal,we can know the stability of Ni₄.The results show that even if the ion source voltage is added to 100 eV,there is a frame fragment of Ni₄.Ni₄ is very stable.The authors used electrospray ionization mass spectrometry to trace Ni_xCd_24-xreaction and found that the Ni₄ framework ruptured when the reaction proceeded for 1 h.Cd（NO₃）₂ was assembled step by step and metal replacement occurred to form multinuclear species Ni_xCd_24-xeventually.