| Non-covalent interactions such as hydrogen bonds(HBs),halogen bonds(XBs),van der Waals interactions and hydrophobic interactions have attracted much attention since they were found important in the design and construction of supramolecular systems.Among them,HBs and XBs are commonly used in crystal engineering,material chemistry and other fields due to their moderate strength,high directionality and adjustability.This thesis focuses on the molecular assembly via HBs and XBs between molecules or ions in solution and solid phase,as well as the role of such non-covalent bonds in the process of crystallization.This will not only help us to understand the process from self-assembly of molecules in solution to crystal formation,but also better guide the design and synthesis of supramolecular materials with specific properties.In the first chapter,the characteristics of non-covalent interactions such as halogen bonds and hydrogen bonds,the nature of these interactions,their applications in biology,material chemistry,crystal engineering,as well as their effects on the crystallization process of materials are briefly introduced.In the second chapter,1,4-diiodotetrafluorobenzene(DITFB)and hydroquinone(HQ)were used as XB donor and HB donor,respectively,and 1,2-bis(4-pyridine)ethylene(BPE)as bond acceptor.We systematically investigated the influence of the crystallization conditions to the final supramolecular products.Surprisingly,it was found that precipitation occurred immediately after mixing the solutions of DITFB and BPE.Through comparative experiments,solid-state reaction and phase transformation experiments,the causes of precipitation were explained by means of X-ray single crystal diffraction,X-ray powder diffraction,scanning electron microscopy,transmission electron microscopy,particle size analysis and DFT calculations.The effects of non-covalent bonds including HBs,XBs and π…π stacking in the process of crystallization were investigated.In the third chapter,phenol and 4-iodophenol were used as hydrogen bond and halogen bond donors respectively,and halides(Cl-,Br-,I-)in tetraalkyl ammonium halide and tetraphenyl phosphine halide as HB or XB acceptors(electron donors).The formation of HBs and XBs by halogen anions in solution and solid phases was investigated by 1H NMR and crystal structure analysis.Generally,the ability of halides to form HBs and XBs depends on their electronegativity and electron donation ability.However,in solution,solvent effect can greatly affect the bonding of halides.Z’>1 in crystallography,viz,more than one molecules of the same type in the asymmetric unit is regarded as the "fossil" of solution.It is extremely important for the understanding of molecular assembly in solution and crystallization.In the fourth chapter,such special crystallographic phenomena were found in the structures of 3,5-bis(trifluoromethyl)benzamide(BTFMBA)and its cocrystal with tetrabutylammonium nitrate(BTFMBA·TBAN).In BTFMBA,the asymmetric unit consists of eight BTFMBA molecules(Z’=8).Every four BTFMBA molecules form a helical chain linked by C-H…O,N-H…O HBs.BTFMBA and TBAN cocrystalize with the ratio of 6:1,and the smallest asymmetric unit contains 24 independent particles(Z"=24).Each NO3-is surrounded by six BTFMBA molecules through HBs to form a disc-like structure.Structural analysis shows that the intermolecular hydrogen bonding played a fundamental role in the appearance of Z’>1 phenomenon,and these hydrogen bonding can be maintained during the nucleation and crystal growth of the corresponding compounds,resulting in the low symmetry of the final structures.The last chapter involves the summary and novelty of this project,and the prospects of non-covalent bonding in designing highly effective sensors for anion recognition and separation,as well as constructing supramolecular materials with diverse structures and functions. |
