Crystal Structure,Magnetism Properties And Formation Process Studies Of Bibenzimidazole Ligand Based On 3d Metal Clusters

The study of polynuclear clusters is an important part of the study of complexes.It has become an interdisciplinary research field spanning inorganic chemistry,organic chemistry,physical chemistry,biochemistry,supramolecular chemistry and material chemistry.The study of polynuclear clusters mainly focuses on the characterization of their solid state properties,and the research on their solution behavior and assembly process is relatively few.The synthesis of polynuclear clusters is usually random,and the directional structure and synthesis are very few.In this paper,we choose a ligand 1,2-di（1H-benzo[d]imidazol-2-yl）ethane-1,2-diol and1,2-di（1H-benzo[d]imidazol-2-yl）ethanol to build a series of polynuclear clusters with Mn²⁺or Ni²⁺by solvothermal.The high-resolution electrospray ionization mass spectrometry（ESI-MS）has been used to study the solution behavior and track the formation process of these clusters,in order to find the possible self-assembly mechanism of polynuclearity clusters.This paper is divided into three chapters:The first chapter is the introduction,the research background and hot issues of polynuclear clusters are systematic introduced in this part.At the same time,we introduced the application of ESI-MS technique in solution chemistry of coordination complexes,which provides new ideas and new methods to the study of clusters.Meanwhile,application of electrospray ionization mass spectrometry in the study of in-situ reaction is introduced.In the second chapter,we take advantage of the early knowledge about this flexible ligand（H₄L）and Mn Cl₂to further explore this series 3d transition metal.We construct two Mn4 cluster with phenomena of metal core rearrangement and ligand in-situ reaction via a mixed H₂O/methanol solvothermal reaction.The origin ligand H₄L forms a cubic tetranuclear[Mn₄^Ⅱ（H₃L）₄Cl₂]Cl₂·5CH₃OH·5H₂O Mn4L4 cluster with Mn^Ⅱ while the H₄L ligand changes its structure to H₃L’forming a high symmetry tetrahedron[Mn₄^Ⅱ（H₂L’）₆（μ₃-OH）Cl]·H₂O·4CH₃OH Mn4L’6 cluster.Precise structural information of coordination clusters is obtained by crystallography,while mass spectra can provide additional information about the cluster in solution and precipitate.A combination of time-dependent ESI-MS,UV/Vis and PXRD has been used to unravel the mechanisms of the formation of Mn4L’6 cluster as well as the rearrangement behavior of the clusters.The Mn4L4 via a{Mn₄}→{Mn₂}→{Mn₁}split process and then[Mn L]translate into[Mn L’]via an in-situ reaction.Finally,{Mn₁}fragments translate into{Mn₂}and then translate into{Mn₄}to form Mn4L’6.[Mn₄L_xL’_6-x]（x=1,2,3,4,5）as a series of intermediate fragments make the process more clearly.In the process of forming[Mn₄L_xL’_6-x],the time that each fragment reaches the highest relative intensity has a very obvious time sequence:[Mn₄L₅L’]→[Mn₄L₄L’₂]→[Mn₄L₃L’₃]→[Mn₄L₂L’₄]→[Mn₄LL’₅].We also used Multi-stage-MS spectra and DFT to calculate the Gibbs free energies of these structural fragments and the result confirmed this transformation mechanism.[Mn₄L_xL’_6-x]spilt to[Mn₂L_yL’_3-y]with energy bombard while[Mn₂L_yL’_3-y]spilt to[Mn LL’]and[Mn L’]with energy bombard.A conclusion is obtained that the in situ reaction is the source power for Mn4L4rearrange to Mn4L’6.Evaluating the crystallinity and possible rearrangement behavior to changes in solution will help to explore new functions and applications of coordination clusters.To the best of our knowledge,it is for the first time such an assembly and competition combine rearrangement process of same nuclear cluster and in-situ reaction process to explore the assembly mechanism of coordination clusters by ESI-MS and confirm the mechanism of competition and transformation among different species.In the third chapter,we construct a Ni6[Ni₆(C₁₆H₁₃N₄O)₃Cl₆（O₂）（CH₃O）₃]Cl·ClO₄·（H₂O）·3（CH₃OH）·HN（CH₃CH₂）(L=C₁₆H₁₄N₄O,1,2-di（1H-benzo[d]imidazol-2-yl）ethanol)cluster contain a rareμ₆-（η¹）O₂^2-bridge.In the synthesis process of Ni6,Et₃N is used as organic base to regulation of acidity and alkalinity.In the Ni6 structure,the ligand keeps the original form.While without Et₃N in the same reaction system,theligand1,2-di（1H-benzo[d]imidazol-2-yl）ethanolchangeto（E）-2-（2-（1H-benzo[d]imidazol-2-yl）vinyl）-1H-benzo[d]imidazole via an in situ reaction to crystallize.Volatilized the reaction solution of Ni6 we got a[Ni₄(C₁₆H₁₃N₄O)₃（CH₃O）（CH₃OH）₃]·4H₂O Ni4 crystal.The high-resolution electrospray ionization mass spectrometry（ESI-MS）has been used to study the solution behavior and track the formation process of Ni6 in order to find the possible self-assembly mechanism.In the MS condition,we find the Ni6 fragments contain O₂^2-.Based on those experimental facts,we track time-dependent ESI-MS on reaction solution to explore to formation of Ni6.In the solution,Time-dependent ESI-MS spectra showed a general trend in assembly process starting from the monomer to the dimer,to the trimer and to the tetramers,finally to sexamer.To find to source of the O₂^2-in the Ni6,we control the volume of air in the reaction system,we got a positive correlation between yield and oxygen content.This from a side,comfirming the O₂^2-source of Ni6 is oxygen in the reaction system.The Ni6 reveals a spin-glass magnetic behavior（φ=0.025886）Evaluating the crystallinity and possible rearrangement behavior to changes in solution will help to explore new functions and applications of coordination clusters.