| Charge transfer cocrystal has been studied for a long time because of the intriguing properties Inspired by the properties of metal-organic frameworks (MOFs), the preparation of organic microporous material is currently of great interest. These molecular crystals containing cavities or channels are prone to be isolated from solution as solvates. The solvent guests play a vital role in stabilizing structure, so the frameworks will collapse as soon as the solvent guests are removed. Thus, it is necessary to explore other strong supramolecular interaction or combination of weak interactions to stabilize the networks to avoid structure collapse after solvent removal.On the other hand, MOFs or COFs are mainly used in gas adsorption, separation and catalyst, few examples for adsorption of aromatics were reported. Due to the charge transfer interaction can be formed between aromatics and electron-deficient compound, it was applied in aromatics adsorption. Electron-deficient groups were embedded in the host molecules, and adsorbed aromatics through charge transfer interactions.In this paper, we prepared one two-component organic charge transfer cocrystal and its eight cocrystal aromatics solvates based on an electron-rich anthracene derivative and electron-deficient 7,7,8,8-tetracyanoquinodimethane (TCNQ). The main results are summarized as following: (1), An anthracene derivative, 1-(5-(anthracen-9-yl)-3-(4-methoxyphen-yl)-4,5-dihydropyrazol-1-yl)ethanone (AMPE) was synthesized. This molecule has two planes, anthracene moiety and pyrazoline plane, and is a T-typed molecule. We selected AMPE molecule as donor and TCNQ as acceptor, and prepared one kind of charge transfer cocrystal and eight cocrystal aromatics solvates by solution evaporation method. Single crystal X-ray diffraction showed that TCNQ adopts a face-to-face sandwich-like mode with the anthracene moiety of AMPE via charge-transfer interactions in all these crystals. Crystal structure of these eight solvates showed that they can be classified two different types according to their stoichiometries ratios, framework arrangements and cell parameters. Solvates 1·toluene (1a),1·chlorobenzene (1b),1·o-chlorotoluene (lc), 1·p-chlorotoluene (1d),1-o-xylene (1e),1·m-xylene (1f), 1·p-xylene-1 (1g) belong to type I solvates with a ratios of AMPE:TCNQ:solvents=2:1:1, while 1-p-xylene-2 (1h) belongs to type Ⅱ solvate with a ratio of 2:1:2. In crystal 1, slit-like pores were formed between AMPE and TCNQ through charge transfer, C-H…π, C-N…π and hydrogen bond interactions. In type I solvates, the aromatic molecules were stabilized in the slitlike pores by different supramolecular interactions. In type Ⅱ solvate, the neighboring racemic chains were connected by one kind of p-xylene molecules through C-H…π interactions and formed square-grid channels. Another p-xylene was located outside the channel.(2) Mechanochemical method was also used for preparation of these cocrystals with the different stoichiometries ratios of AMPE and TCNQ,1:1 and 2:1, neat grinding and solvent-assisted grinding were applied. The products obtained were analyzed by DSC/TGA and PXRD. It showed that two-component cocrystal can not got by neat grinding, but aromatics solvates can got by aromatics-assisted grinding. However, the products of 1:1 consist of 1:0.5 cocrystal and 0.5 TCNQ.(3) Cystal transformation was studied between 1 and type I solvates. Take la (1·toluene) for example, crystal la (1-toluene) was changed to crystal 1’when subjected to 170℃ at normal pressure. Although many of the crystals become opaque upon desolavtion, several SCD-qulility crystals still remained intact, which is revealed by single crystal X-ray diffraction. Similarly,1’could also be obtained by removing the solvents from other type I and type II solvates.(4) In order to investigate the reversibility of the transformation from crystal 1’to solvates, crystal 1’were immersed in these aromatics. It was found crystal 1’can accommodate these aromatics to form corresponding type I solvates la-1g. when the same experiment was done in p-xylene, only type I solvate 1g was got, no type II solvates 1h was generated even at a lower temperature. These results indicate that transformation from 1 to type I solvates la-lg was an adsorption process, not a dissolution of cocrystal and re-crystallization process. What’s more, when crystal 1 was immersed into non-aromatic solvents, such as CH2Cl2, acetone, methanol, cyclohexane, tetrachloroethylene, it was found that 1 shows no adsorption for these non-aromatic solvents. Thus, it was indicated that crystal 1 showed a selective adsorption for aromatics. Additionally, N2 adsorption experiments was perfprmed and it was found that the BET surface area is 68.229 m2g-1.The above studies showed that cocrystal 1 and its solvates can reversible transformed. |
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