Real Time Tracking Of The Formation Process,Assembly Step By Step And Doping Mechanism Of The M₇ Disks From Square-Planar Ni Monomers And Research On Photocatalytic Performance For Water Oxidations

High nuclear transition metal clusters,with their fascinating spatial configurations,excellent magnetic properties and favorable catalytic performance,render the research area of coordination chemistry a major focus.In particular,although cobalt and nickel heterometallic clusters exhibit similar coordination geometries,and chemical properties,their different electronic configurations can lead to different physical properties.However,the mixed-metal(Co-Ni)complexes can enhance certain properties with respect to their pure compounds,although the difficulty in in identifying each nucleus using the traditional single-crystal diffraction techniques.Thus a very interesting research topic to study the rich information of the coordinated clusters in the solution and reveal the relevant assembly mechanism is the ESI-MS technique.Meanwhile,given the isotope distributions of cobalt and nickel atoms are different,the ESI-MS technique will solve the distribution of the different atom in the solution.In this thesis,the square-planar monomeric units(NiL2)were found to react with M(H2O)6(ClO4)2(M=Ni/Co)in CH3CN to give the heptanuclear compounds at room temperature and have a regular doping ratio structure of heterometallic heptanuclear clusters.The ESI-MS technique was used to allow one to catch the reaction process after intensive research.This thesis is divided into three chapters:The first chapter is the introduction to the research background and current research focus of transition metal clusters,focused on electrospray ionization mass spectrometry applications in the study of the transition mechanism of solution properties and assembly of metal clusters themselves.It also describes the transition metal clusters photocatalytic analog "photosynthesis"with the relevant background and current progress.Finally,the significance of the topic and the progress of the thesis are presented.Chapter II describes 2-ethoxy-6-((methylimino)methyl)phenol(HLa)as ligand to synthesise the square-planar monomeric units Ni?(La)2,which as a starting material was found to react with Ni(ClO4)2/Co(ClO4)2 to give the heptanuclear compounds,{[M7(La)6(OH)6]·(ClO4)2·2(CH3CN)}[Ni7-a/(CoNi)7]and their 1:1 co-crystal structures {[M7(OH)6(La)6]·(ClO4)2-[Ni(La)2]·2(CH3CN)}[Ni7+1,(CoNi)7+1]in acetonitrile solvent.Using high-resolution mass spectrometry for on solution of one single crystal,we found the following interesting phenomenon:firstly,Ni1-a single crystal self-assemble to form the[Ni2L3]+ion fragment(m/z=650)in solution.Secondly,under MS conditions,this peripheral ligands ethoxylates,methylene amino of the dics like heptanuclear will depart and inner-bridge ligands ?3-OH is replaced by ?3-OCH3,resulting in heptanuclear mass peak split into five adjacent peaks.Thirdly,the co-crystal structure of M7+1 is formed due to supermolecular force between the monomer and the heptanuclear.Changing the MS experimental conditions and adjusting the scope of data collection at m/z=1100-1500,we found that ion peaks of characteristic of co-crystal structure ?[Ni7(La)6(OH)6]·[Ni(La)2]2·3H2O}2+ at m/z=1205,which is the first observed clusters of weak supramolecular forces using mass spectrometry techniques.The mechanism of the reaction from Ni1-a to the heptanuclear clusters and their co-crystal structures has three aspects.First of all,visual observations using transparent glass bottles and high-expansion microscope,the transformation of monomer to co-crystal is clear.Secondly,each species changing in the reaction solution rely on electrospray ionization mass spectrometry,tracking the reaction solution in a specific period of time,and Ni1-a toward to heptanuclear cluster M7 and M7+1 "Bottom-to-Up" changes were successfully observed.Following the reaction as a function of time with mass spectrometry(MS),two key reaction intermediates are found where the transient[Ni2(La)3]+ fragment(m/z=650)rapidly turned to[Ni4(OH)2(La)4]2+(m/z=490)under basic condition and then to the final cluster.According to the intermediate fragment content variation,combining with the structural characteristics of the compounds,the Ni1?[M2?M4]?M7 step-by-step assembly process of the reaction is revealed.Finally,the timedependent powder diffraction results confirm the solid phase complexes.There are some huge challenges for simulating the heterometallic cluster MS data:(a)the metal ions competition,and(b)every mass peak has many species are superposed.The author puts forward related mathematical formulae in view of statistical methods,and calculates the content of each species that exists to account for possibly combinion with the abundance and distribution of mass isotope peaks.Then the reaction time of the doping ratio of cobalt and nickel are obtained:the range for Ni is 32%-42%and Co is 68%-58%.This conclusion provides more convenience for the subsequent doping research work.Herein we use the above disc-like heptanuclear structures characterized homogeneous Co/Ni clusters compounds that catalyze water oxidation under a common photochemical system.The experiments were carried out in 0.5 M KBi solution containing 0.5 mM[Ru(bpy)3]2+as the photosensitizer,35 mM K2S2O8 as the sacrificial electron accepter,and 0.1 mM metal cluster compound as the catalyst.The initial turnover frequencies were calculated for the initial 30 seconds.The TOF of the(CoNi)7,(CoNi)7+1,Ni7-a and Ni7+1 are 0.46,0.42,0.23 and 0.14 respectively.Chapter 3 develops the effects of changing the ligand size,and repeats the experiment as the second chapter,and makes a comparison of the above experiments.This chapter involves two ligands,2-ethoxy-6-((methylamino)methyl),phenol(HLb)and 2-(iminomethyl)-6methoxyphenol(HLc),which were used to synthesise other monomeric units Ni?(Lb)2(hereinafter referred as Ni1-b)and Ni?(Lc)2(hereinafter referred as Ni1-c).Using the two monomeric units as raw materials to react with Ni(ClO4)2 and the use of ESI-MS to track the reaction process in real-time at room temperature.The reaction Ni1-b and Ni]-c are not as good as Ni1-a response quickly and thoroughly from a macro point of view;the Nil-b does not take place at room temperature and Ni1-c partly transforms to[M7(Lc)6(OH)6]·(ClO4)2·2(CH3CN)(hereinafter referred to as Ni7-c),there are two kinds of crystal Ni1-c and Ni7-c.In solvothermal reaction,Ni1-b still does not react,while Ni1-c all converts into Ni7-c crystals.In addition,both reactions do not give the co-crystals.ESI-MS study of real-time tracking of the reaction process get more complex spectra where more ion fragments are present,although there are Ni1,Ni2,Ni4 and Ni7 peaks,there is no clear trend.This result also proves that,Ni2 and Ni4 intermediates will generate in such systems.It is worth mentioning that,despite Ni1-b does not react with Ni(ClO4)2 in room temperature when we do not find the macro Ni7-b generation,then the fragment[Ni7(OH)6(Lc)6]2+ is the highest peak which is found during the reaction under MS conditions.Maybe the reaction cannot reach the energy barrier due to the room temperature so the reaction did not occur.But the heptanuclear is found in MS weak energies conditions.