Study On The Two-component Systems With Potential Intermolecular Halogen Bonding Beyond Crystal Engineering

Halogen bonding(XB)is a kind of noncovalent interaction similar to hydrogen bonding,which has important application in crystal engineering,pharmaceutical industry,biological system,and material science,hence attracting extensive attention of scientists.Although great progress has been made in this field,many basic problems such as controlled self-assembly exist,impelling the study of halogen bonding still a hot research topic.For some specific systems,the relatively weak bond strength is not conducive to the formation of co-crystal,which limits the determination of the bonding features.In this sense,this thesis focuses on the study of two-component systems with potential intermolecular halogen bonding using the methods beyond crystal engineering.It aims to provide a new way to detect the weak bonding and the structural assembly in amorphous systems.In the first chapter,the halogen bonding and its application were introduced briefly,and the influence of the strength of intermolecular interaction on molecular self-assembly was discussed;afterwards,the significance of host-guest chemistry in investigating intermolecular interactions were described,followed by the introduction of crystalline sponge method(CSM)in the field of supramolecular chemistry;finally,the purpose and research significance of the thesis were pointed out.In the second chapter,1,3,5-trifluoro-2,4,6-triiodobenzene(TFTIB)and 1,4-diiodorfluorobenzene(DITFB)were used as halogen bonding donors,triphenylphosphine(PPh3),4,4’-bipyridine(Bipy),N,N’-diphenylthiourea(DPT),N,N’-dimethylthiourea(DMT)were used as halogen bonding acceptors to construct two-component systems possibly in terms of co-crystal,eutectic and mechanical mixture.The study were conducted by means of X-ray powder diffraction,nuclear magnetic resonance and melting point phase diagram.The factors influencing the solid forms were analyzed from the molecular level,and it was found that the form of the packing state was actually the comprehensive competition results among the donor-acceptor interactions,the interactions between the same tye components,and the donor/acceptor-solvents interactions,where it precipitates from.In short,the strong donor-acceptor interactions prefer to result in co-crystals;the weak interactions often lead to the formation of eutectic;while,the lack of effective intermolecular forces tend to give rise to the mechanical mixture.The results in this chapter provided a rapid and purposeful method to screen the solid-state form in terms of co-crystal,eutectic and mechanical mixture.In the third chapter,to probe the potentially weak halogen bonding between the donor and acceptor systems in non-cocrystal form,we tried to use the method beyond crystal engineering,viz.host-guest chemistry.In detail,the classical ZnI2-TPT crystalline sponge was used as supramolecular host to simultaneously capture halogen bonding donors(1,4-diiodorfluorobenzene,pentafluoroiodobenzene,1,4-diiobenzene,iodobenzene,etc.)and acceptors(methyl p-toluenesulfone,1,4-dioxane,etc.)as two different types of guests.The adsorption capacity of crystalline sponge to these two different types of guests and the interactions between host-guest and guest-guest were studied via single crystal X-ray crystallography.It was found that the-ZnI2 sites on the host framework tended to provide electrons to the halogen bonding donors forming halogen bondings,while the TPT sites tended to interact with the electron donors(halogen bonding acceptor)by the C-H groups or π systems.Therefore,the halogen bonding between the donors and acceptors molecules as the guests could not effectively form under the influence of the host framework.Instead,the lone pair…π and weak hydrogen bonds could be detected between the two guests.In addition,in another system,11 independent pyrrole molecules were orderly "encapsulated" in the cahnnel of the crystalline sponge channel.The structure and the assembly of the "liquid" pyrrole were accurately characterized.It showed that the intermolecular N-H…π interaction could connect pyrrole molecules into dimer,tetramer,pentamer and other assembly states.The study provided a strategy for further understanding of intermolecular interaction and molecular aggregation in solution.In the fourth part of the thesis,polymorphism phenomenon of 2,4,6-tris(4-pyridyl)-1,3,5-triazine(TPT),the ligand of ZnI2-TPT crystalline sponge,was investigated.By means of X-ray single crystal diffraction,thermal analysis,X-ray powder diffraction,analysis of molecular interaction and energy decomposition analysis based on single crystal structures,the relationship between the crystal phase and its macroscopic properties were established,and how the intermolecular interaction affected the stacking,mechanical properties,stability and optical properties of crystalline compounds were revealed.These results could provide a reference for the construction of single crystal materials with required structures and target properties.The last chapter summarized the whole thesis,emphasized the innovation of the work,and also prospected the potentials of the study of supramolecular systems beyond crystal engineering.