JACS: supramolecular organic framework based on Schiff base macrocycles

The adsorption separation of mixed gas depends on the difference of adsorption capacity of solid adsorbent for each component The efficiency of this separation technology mainly depends on the performance of various adsorbents As early as the 1950s, people began to use activated carbon, diatomite, acid clay and other adsorbents for gas separation, but these original adsorption materials not only have poor adsorption capacity, but also can not be recycled, so they can not meet the needs of industrial production Since the 1960s, a variety of new synthetic adsorption materials, such as synthetic zeolite molecular sieve, modified activated carbon, adsorption resin and so on, have made great progress in adsorption separation technology Since the beginning of the 21st century, porous organic materials have been widely used in the fields of selective gas separation due to their excellent properties, including COFS, pops, SOFS and so on Recently, Professor niveen M khashab of King Abdullah University of science and technology in Saudi Arabia and his collaborators reported a supramolecular organic framework t-sof-1 (Fig 1) based on Schiff base macrocycle, which not only has stable pore structure, but also can effectively adsorb CO 2 in the air In addition, the pore size can be adjusted by introducing other guest molecules The author introduced iodine atom to make the organic framework show excellent separation ability of CO2 / CH4 This achievement was published in the Journal of the American Chemical Society (DOI: 10.1021 / JACS 8b08770) under the title of "triangle based supramolecular organic framework with permanent intrinsic poverty and tunableselectivity" Fig 1 Crystal structure and stacking diagram of macrocyclic molecules (photo source: J am Chem SOC.) synthesis of Schiff base macrocycles is relatively simple The equivalent 1,2-diaminocyclohexane reacts with p-phenylenedicaldehyde in methanol to obtain Schiff base macrocycles precursor, and then the triangular Schiff base macrocycles are obtained by reduction of sodium borohydride Although both H NMR and C NMR can characterize the structure and purity of the compounds, crystal structure analysis is still the most direct and effective way to obtain the molecular structure Due to the influence of solvent on the crystal form and accumulation of such molecules in crystal cultivation, the author had to convert the large ring of Schiff base into salt, that is to say, all the amino groups in the structure were protonated In this way, the author successfully obtained the crystal structure of the compound (Fig 1) The analysis of single crystals shows that the synthesized Schiff base macrocycles do have a triangular structure, and it is very interesting that these triangular macrocycles will spontaneously gather together to form a hexagonal structure In addition, it is found that the size of the triangle area is about 6.3 Å, and there is a space of about 4.5 Å in the center of the hexagon surrounded by six triangles Fig 2 A) N 2 adsorption desorption isotherm curve of t-sof-1; b) N 2 and CO 2 adsorption desorption experiment (photo source: J am Chem SOC.) after determining the molecular structure of the material, the author characterized its pore structure The adsorption desorption isotherm curve of N 2 shows that the material based on the large ring of Schiff base belongs to microporous material (Fig 2a), and its specific surface area is about 170 M 2 / G by calculation In addition, due to the high proportion of amino group in the material structure and the appropriate pore size, the author speculates that the material may have a unique adsorption capacity for CO2, and the experimental results also support the author's conjecture The experiment shows that at 760 Torr, the adsorption capacity of t-sof-1 to CO2 can reach 23 cm 3 / g, while the adsorption capacity of material to N2 under the same conditions is less than 5 cm3 / g (Fig 2b) Fig 3 Preparation of I @ t-sof-1 and its crystal structure (left), adsorption desorption experiment of I @ t-sof-1 and t-sof-1 (right) (photo source: J am Chem SOC.) in order to further improve the separation performance of the material, the author introduced other guest molecules to regulate the pore size of the material, and the selection of guest molecules is mainly referred to Because of the pore size of the material itself, iodine (< 4.5 μ) with smaller molecular size was selected as the guest molecule The author obtained the supramolecular organic framework I @ t-sof-1 containing iodine by immersion in acetonitrile (left in Fig 3), and carried out gas adsorption desorption experiment on it (right in Fig 3) The results show that under the same conditions, the supermolecular organic framework containing iodine shows excellent separation ability of CO2 / CH4 Highlight of this paper: Based on Schiff base reaction, a triangular macrocyclic compound was synthesized, and a supramolecular organic framework with gas adsorption capacity was prepared by using this compound In addition, the organic framework showed excellent CO 2 / CH 4 separation ability after the introduction of iodine atom The full text is written by Arnaud Chaix, georgesmouchaam, Aleksander shkurenko, Phuong Hong, basem Moosa, Prashant M Bhatt, Karim Adil, Khaled n Salama, Mohamed eddaoudi, and niveen m khashab