| Spin-crossover(SCO)functional molecular materials currently have great applications in molecular switches,information storage and other fields,but there are still huge challenges in bringing them from basic scientific research to practical applications.Although there are many types of spin crossover,only abrupt SCO with near room transition temperature and larger thermal hysteresis loop width can meet the demands of daily information storage,and thus many chemists focus their attention on this.The spin crossover performance can be modified by the non-covalent interactions,but the synthesis of ferrous spin crossover complexes with controllable non-covalent interactions is remain a big challenge.In addition,the introduction of new substituents into the known system,especially the substituents with other functions that can be coupled with SCO,has also attracted many interests in the spin crossover.However,due to the limitation of synthetic methods,this field is still being explored.In this thesis,given the impact of counter ion and substituent on the SCO behavior,a seris of mononuclear compounds with FeⅡN6 octahedral coordination geometry were fabricated by bistetrazolium ligands,and spin crossover behavior of them was systematically investigated.This thesis will be explained in the following four parts:1.Introduction section,overview and classification of spin crossover as well as the regulation of spin crossover are introduced;Research progress and development status of tetrazolium organic chelating ligands in the field of spin crossover are reviewed.According to the literature review,we put forward the topic basis and the significance of this research.2.In this section,modulation of spin crossover complexes by supramolecular interactions is introduced.A series of solvent-free FeⅡ compounds(Al)2[FeL12]were synthesized and characterized based on pyridine bistetrazolium ligands and seven different amine counter cations,(H2L1=pyridine-2,6-bistetrazolium,A1=(Me)4N+1;Et2NH2+2;iPr2NH2+3;iPrNH3+4;(Me)3NH+5;iPr2MeNH+6;TPre2EtNH+7).The singlecrystal data show that complexes 1-7 are all supramolecular frameworks containing the same(FeL12)center,but with different packing modes,1 is a three-dimensional framework,2-4 is a one-dimensional chain,while 5-7 is a two-dimensional layer.The spin state of complexes 1-4 can be confirmed based on single-crystal X-ray diffraction at different temperatures.The temperature-dependent magnetic susceptibility measurements indicate that complex 1 exhibits a low spin state(belwo 350 K),complex 4 maintains its high spin in 2-400 K temperature range,2 and 3 undergo spin-crossover behavior with transition temperature close to room temperature.Interestingly,a strong cooperative between the spin crossover centers is observed in complex 3,which shows an abrupt spin crossover with a transition temperature near room temperature(9℃)and an 8 K thermal hysteresis loop width.The investigation of this chapter reveals the importance of molecular packing generated by the different organic cations in regulation SCO behavior and offers a new insight for the design of SCO compouds with near room temperature transition.3.Modulation of spin crossover complexes by different substituents is investigated in the section.Five kinds of bistetrazolium pyridine ligands with different substituents were obtained through multi-step organic synthesis reactions.The assembly of the above mentioned ligands with FeⅡ results in six type complexes(A2)2[FeL2-62],which are characterized and analyzed by NMR,MS,single crystal,UV and other test methods.Temperature-dependent fluorescence and magnetic measurements show that complex 13 has synergy between spin crossover and fluorescence.4.In the end,the research work of this thesis is summaried on the basis of the above research contents,and the development directions as well as research hotspots in SCO materials are prospected. |
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