Synthesis And Crystal Engineering Studies Of Polypodial Pyrrole Carboxylates

Supramolecular chemistry is a science that studies the supramolecular systems with specific structures and functions of two or more chemical species through molecular interactions.It is an interdisciplinary subject that has developed rapidly in the past 40 years.Crystal engineering is the design of molecular solids.It uses the interactions between molecules to design and synthesize functional solid structures through neutral or ionic structural units.The driving force of the formation of supramolecular system can be formed through hydrogen bond,so the field of hydrogen bond self-assembly is also one of the hot research topics in chemistry,and plays a positive role in the research of chemistry,biology,materials and other fields.In this paper,we use the double N-H···O hydrogen bond formed between pyrrole N-H and carbonyl C=O as a synthon of hydrogen bond self-assembly to regulate the self-assembly of compounds.On this basis,we designed and synthesized two series of14 pyrrole carboxylate compounds,and analyzed the crystal structures of eight of them by X-ray crystallographic studies.This paper is divided into three parts,the first part is the introduction.This part mainly introduces the definition and development of crystal engineering,supramolecular chemistry,supramolecular self-assembly and hydrogen bond self-assembly,and summarizes the hydrogen bond self-assembly of some pyrrole compounds.In the second part of this article,we take the design and synthesis of hydrogen-bonded self-assembled supramolecular compounds as the main line,and introduce the synthesis process of two series of pyrrole carboxylate compounds.Including 9 kinds of multi-foot pyrrole carboxylate compounds and 5 kinds of5,5’-dipyrrolemethane carboxylate compounds,and the structure of the compounds was confirmed by ¹H NMR,MS,and ¹³C NMR.In the third part,we studied the crystal structures of 8 compounds by X-ray single crystal diffraction technique.Among them,compounds 1,2,3,4 and 5 are all self-assembled into remarkable supramolecular structures by R₂²（10）hydrogen bond motif.These results indicate that double hydrogen bond synthon I is relatively stable and can be applied to the design and regulation of supramolecular self-assembly structures.In addition,compound 5·CH₃OH was assembled into a band-like structure by the C₂²（7）type hydrogen bond motif,and thermogravimetric analysis was performed on it.The observed results of two compounds 2 and 5 were obtained by scanning electron microscopy.Compound 7 is a tetrapodal pyrrole carboxylate compound with symmetrical structure,the syn and trans conformations of the pyrrole carboxylate arms are half and half.Finally,a one-dimensional network structure is obtained along the two N-H···O hydrogen bond extension directions.Compound 9was a hexapod pyrrole carboxylate compound with symmetrical structure,and its two-dimensional supramolecular structure was obtained by self-assembly.Compound12·CH₃OH is the only crystal of 5,5-（pentane-3,3-diyl）bis（1H-pyrrole-5-carboxylate）compound,and has a crown ether structure.In its crystal structure,the arms of pyrrole carboxylate are trans conformation,so there is no synthon I formed.By analyzing the crystal structure of most of the above compounds,the results show that the hydrogen bond formed between two pyrrole-2-carboxylate groups has sufficient stability and reliability,which can be used in crystal engineering and hydrogen bonded organic frameworks（HOFs）material design.