Study On Design And Structure Of Co-crystal Based On Pyridyl Group

Due to the clear crystal structure,co-crystal is a perfect model for studying the relationship between structure and properties in chemistry.At the same time,compared with the traditional single crystal,the multi-component co-crystal also brings more abundant structural and chemical information.The main research work in this article aims at molecular recognition and supramolecular interaction.It is of great significance to design new co-crystal materials and study the properties of co-crystals in different environments.Raman and fluorescence detection techniques at high pressures and scanning tunneling microscopy can be used to clearly study the structural changes of crystals caused by external stimuli.The changes of eutectic properties can be shown by fluorescence spectra.And Clear and visible structural and property changes are interrelated,which is helpful to further understand the relationship between structure and performance.Based on this,this study includes the following two parts:4,4’-(1,3-propanediol)bispyridine(TMDP)and 1,3,5-trifluoro-2,4,6-triiodobenzene(3F3I)were dissolved in 1-phenyloctane separately and then mixed in equal molar amount to drop on the interface of highly oriented pyrolytic graphite(HOPG).The two-dimensional co-crystal structure was formed by TMDP and 3F3 I in solution.The two-dimensional crystal structure at the interface of HOPG was observed in detail by STM.Due to the presence of the HOPG interface,the molecules have more attachment sites when forming crystals.These attachment sites not only make the crystals tend to planarize,but also affect the form of formation of halogen bonds between two different chemical components.All of the monomers in co-crystal have only two iodine atoms forming a halogen bond with the adjacent nitrogen.Under the same experimental condition,the HOPG was replaced by the Au(111)plane.It was confirmed by the experiments that the assembly on the Au(111)interface did not form an effective identification assembly but disordered.In addition,TMDP and 3F3 I were separately cultured in a mixed solution of petroleum ether and tetrahydrofuran to obtain a three-dimensional co-crystal structure.The IV detailed unit cell structure was obtained by single crystal diffraction.Some 3F3 I monomer molecules in the three-dimensional crystals do not form a halogen bond with N on the TMDP,and the other three iodine atoms all form a halogen bond.Compared with the two-dimensional crystals,three-dimensional crystals have smaller packing density,which indicates that three-dimensional crystals are looser.After studying the influence of interface on crystal growth,in the second part of this paper,the structural changes and new properties of this crystal under high pressure environment were studied.Most studies on the response of materials to external stimuli focus on the two properties of temperature and pressure.After the invention of high-pressure devices,especially high-pressure anvils,the study of high pressure extends from liquids and gases to solids.In this work,our group used 3F3 I and 1,4-diiodotetrafluorobenzene(4F2I)to obtain two three-dimensional co-crystals with the culture of TMDP respectively,then pressurized under high pressure on the anvil.Combined with Raman technique and fluorescence technique,the characteristic peak of Raman of the co-crystal obtained by 4F2 I and TMDP culture moves toward the high wavenumber after the pressure.This is because that the increase in pressure causes the distance between the molecules to become closer.In addition,as the pressure increases,the fluorescence becomes stronger at around 8 GPa,which is because the increase in pressure makes it possible to form a charge transfer by making the distance between molecules closer.Charge transfer enhances fluorescence.At the same time,it was found that the fluorescence of the crystal remained well after unloading the pressure,and did not perform fully reversibly.The co-crystal of 3F3 I and TMDP did not show obvious fluorescence increase during the pressurization process,and red fluorescence was maintained after the pressure releases.After high pressure,the red fluorescence of the crystal is mainly due to the crystal disturbance at high pressure and the emergence of new electron transfer states in the crystal.Detailed study of the both two-dimensional and three-dimensional co-crystal structure differences of the same composition and the factors affecting the two-dimensional co-crystal growth can be significant for further understanding the two-dimensional co-crystal growth mechanism and laying a good foundation for the subsequent directional preparation of co-crystals.Two different kinds of co-crystals were formed by two similar ligands and the same host.The co-crystal structure and properties were studied by spectroscopy under high pressure.The study on the regulation of the structure and properties of co-crystals is helpful to the development and application of co-crystals properties.