Conformational Control Of N,N’-bis(4-pyridyl)-benzenedicarboxamide Derivatives In Various Crystals By Intramolecular Hydrogen Bonding

As a directional noncovalent interaction,hydrogen bond plays an important role in the synthesis of crystals.Rationally designed hydrogen bonds can facilitate the formation of the desired molecular conformation and packing mode in crystals,thus change the chemical reactivity and physical properties.Although the conformational mobility of flexible aromatic amides provides a way to generate structural diversity in the crystalline structure,strategies are needed to promote a conformational preference based on the rational design.In this dissertation,three N,N’-bis(4-pyridyl)-benzenedicarboxamide derivatives were designed and synthesized based on the intramolecular hydrogen bond between an amide NH and an alkoxy group.Organic crystals and metal complexes containing these compounds were prepared.By analyzing the structural characteristics of N,N’-bis(4-pyridyl)-benzenedicarboxamide derivatives in various crystals,the control of molecular conformations by the intramolecular hydrogen bonding is discussed in detail.In the second chapter,two methoxy groups were introduced onto N,N’-bis(4-pyridyl)isophthalamide(bpi)in order to limit partial intramolecular rotation by the intramolecular hydrogen bonding.We synthesized 4,6-dimethoxy-N,N’-bis(4-pyridyl)isophthalamide(dmbpi),and further prepared nine dmbpi-containing organic crystals.Single crystal X-ray diffraction revealed that all dmbpi molecules in these crystals adopt the anti,anti-conformation owing to the intramolecular hydrogen bonding.In contrast,the diverse conformations of bpi molecules in the 27 bpi-containing crystals are categorized into three types.The remarkable difference in the conformational distribution may be attributed to that the energy gaps between the different conformations of dmbpi are significantly greater than those of bpi on the basis of density functional theory calculations.These results demonstrate that the introduction of suitable hydrogen-bond acceptors onto an aromatic amide to form intramolecular hydrogen bonds is an effective and rational strategy to achieve a desired conformation of molecules in crystals.In the third chapter,by introducing two methoxy groups onto N,N’-bis(4-pyridyl)terephthalamide(bpt),we synthesized 2,5-dimethoxy-N,N’-bis(4-pyridyl)terephthalamide(dmbpt),and further prepared four organic crystals and eight metal complexes.The structural analysis shows that 90% of the amide NH groups of dmbpt molecules forms the expected intramolecular hydrogen bonds with the methoxy groups.Thirteen of fifteen dmbpt molecules adopt the anti,anti-conformation with the intramolecular hydrogen bonds formed on the both sides.Generally speaking,there is a high probability of the existence of the anti,anti-conformation in various dmbpt-containing crystals owing to the rational introduction of hydrogen bond acceptors onto a bpt molecule.This demonstrates that intramolecular hydrogen bonds can effectively restrict the intramolecular rotation between benzene and amide groups in organic crystals and metal complexes,as concluded in the second chapter.In addition,among these complexes,dmbpt-5 is a two-dimension metal-organic framework(MOF),and dmbpt-6 is a three-dimensional MOF.These two MOFs can be simultaneously produced in the same reaction vessel,and their ratios in the product can be controlled by changing the concentration of the reactants.Regarding structural relations,the three-dimension framework of dmbpt-6 may be regarded as coordinate-bonded twodimension frameworks,which can be found in dmbpt-5.In the fourth chapter,by introducing an ethylenedioxy group onto the bpt molecule,we designed and synthesized a new linear building block,N,N’-bis(4-pyridyl)-1,4-benzodioxan-5,8-dicarboxamide(bpbd).Five organic crystals and five metal complexes were prepared by using bpbd.In these crystals,79% of the amide NH groups of bpbd molecules forms the expected intramolecular hydrogen bonds with the ethylenedioxy groups.In comparison with the dmbpt-containing crystals presented in the third chapter,it is found that dmbpt is significantly biased toward an “N-shaped” conformation by the intramolecular hydrogen bond,whereas bpbd tends to form an “Ω-shaped” conformation to some extent.It is concluded that the introduction of hydrogen bond receptors at different positions of bpt can rationally modulate the conformational preference of the molecules.