Research On Single Crystal Transformation,solution Behavior And Magnetic Properties Of 3d Metal Cluster Based On Benzimidazole Ligands

For the past decades,the study of polynuclear cluster is the central part of the coordination chemistry,and it has become an interdisciplinary subject covering inorganic chemistry,organic chemistry,physical chemistry,biochemistry,supramolecular chemistry and materials chemistry.Functional materials with properties that can be manipulated by external stimuli(such as light,heat,pressure,guest molecules)are attracting increasing interest for their potential applications as switches and sensors.In order to understand the origin of the changes in properties,structural,information at different functional states is necessary.In this regards,single crystal to single crystal(SC-SC)transformations of functional material are very helpful because retention of single-crystalline state can directly and accurately reveal the relationship between the structure and properties.But nowadays most case of SC-SC transformations forcus on the Metal-Organic Frameworks(MOFs),because it is not easy to keep the crystalline-state in the cluster compounds;On the other hand,the research of polynuclearity clusters always focuses on the characterization of their solid-state properties,but the works about their solution behavior and self-assembly process are still rare.That is why polynuclearity clusters are usually obtained in a "serendipitous"way.In this thesis,we choose the key ligands with that have the coordinating atoms pointing on one side of the molecule to synthesize a series of polynuclear cluster by solvothermal with the Fe3+ and Co3+ metal salt.The X-ray diffraction,magnetic characterization,high-resolution electrospray ionization mass spectrometry(ESI-MS)and High-Field Electron Paramagnetic Resonance(HF-EPR)measurement were used to study the Single-crystal-to Single-crystal transformation process,and give a possible mechanism to explain the transformation between the gas-solid reaction.This paper is divided into three chapters:The first chapter is the introduction,the research background and hot issues of polynuclearity clusters were introduced in this part.At the same time,we introduced the progress on the cluster that involved the SC-SC transformation,and the main research method that adopts.And the single-molecule magnets always a hot part research for the chemist or physicist.We also introduce the application of ESI-MS technique in solution chemistry of coordination complexes,which provides new ideas and new methods to explore the solution behavior of clusters.In chapter 2,we report that exposing a tetranuclear compound[Fe4?(Nbm)4Cl4(CH3OH)4](where the HNbm=N-Methyl-1 H-benzoimidazol-2-yl)-methanol)(1)to ambient enviroment for 24 hours yielded[Fe4?(C9H9N2O)4Cl4(OH)4]·4H2O(2)with the color change from greenish yellow to black.Obviously,it is a rare phenomenon that a coorderation molecular cluster undergoes oxidative conversion to a new compound through the SCSC process with.The oxidation process was traced by X-ray diffraction,magnetization,and high frequency electron paramagnetic resonance techniques.Magnetic measurements showed that ferromagnetically coupled Fe? ions in 1 were oxided into antiferromagnetically coupled Fe? ions in 2.High frequency electron paramagnetic resonance(HF-EPR)spectra of 1 are consistent with the Fe(?)cluster with the high-spin state and large zero-field splittings,while the HF-EPR spectra of 2 indicate a low spin molecule with relatively small zero-field plitting,supporting antiferromagnetical coupling in 2.Besides,when the reaction solution was left in the air for evaporating,a yellow block crystal(compound 3)were isolated,and it is a new Fe7 cluster with a six-pointed star topology,featuring a tetrahedral iron ion at the center,and joins a small family of Fe clusters based on the ligands Nbm.In chapter 3,by using the ligand(1H-benzimidazol-2-yl)methanol as the mian ligands and the bridge ligand azide under vary temperature thermal condition,obtained a three different Cobalt-base cluster,namely[Co2(Hbm)4(N3)2](NO3)2(CO2),[Co7(bm)12](NO3)2·2(CH3OH)(C07),[Co12(bm)15(N3)7](NO3)2·2(CH3OH)·2(H2O)(Co12).It is well-established that different crystal structures can result from the same starting materials under different synthetic conditions.To study the solution behavior of Co12 cluster,this complex has been dissolved in methanol and detailed measured by high-resolution ESI-MS.The ESI-MS results show that Co12 maintains the disc integrity in solution with very complex coordination dissociation equilibrium.and the inner N3-bridge could be partly replaced by CH3O-and OH-bridges,the ligands could be lost from the disc compound and interesting substitution reaction between the OH-or N3-ions in solution was also observed,which usually occurs during the ESI process as previous reports.And then,by using electrospray ionization mass spectrometry and single crystal diffraction techniques,the self-assembly process of this Co12 cluster has been studied from the reaction parent solution state.Several intermediate cluster,Co2,Co4,Co7,Co10 were identified,these species are important intermediates of the final product.The study of assembly process and reaction mechanism of polynuclearity clusters,will be conducive to build more polynuclearity clusters with novel structures and special properties.Further more,this study can provide us more theoretical basis to control the synthesis of polynuclearity clusters.