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Structural, energetic, and dynamic insights into the abnormal xylene separation behavior of hierarchical porous crystal.

Lin JM, He CT, Liao PQ, Lin RB, Zhang JP - Sci Rep (2015)

Bottom Line: Separation of highly similar molecules and understanding the underlying mechanism are of paramount theoretical and practical importance, but visualization of the host-guest structure, energy, or dynamism is very difficult and many details have been overlooked.Here, we report a new porous coordination polymer featuring hierarchical porosity and delicate flexibility, in which the three structural isomers of xylene (also similar disubstituted benzene derivatives) can be efficiently separated with an elution sequence inversed with those for conventional mechanisms.More importantly, the separation mechanism is comprehensively and quantitatively visualized by single-crystal X-ray crystallography coupled with multiple computational simulation methods, in which the small apertures not only fit best the smallest para-isomer like molecular sieves, but also show seemingly trivial yet crucial structural alterations to distinguish the meta- and ortho-isomers via a gating mechanism, while the large channels allow fast guest diffusion and enable the structural/energetic effects to be accumulated in the macroscopic level.

View Article: PubMed Central - PubMed

Affiliation: MOE Key Laboratory of Bioinorganic and Synthetic Chemistry, School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou 510275, P.R. China.

ABSTRACT
Separation of highly similar molecules and understanding the underlying mechanism are of paramount theoretical and practical importance, but visualization of the host-guest structure, energy, or dynamism is very difficult and many details have been overlooked. Here, we report a new porous coordination polymer featuring hierarchical porosity and delicate flexibility, in which the three structural isomers of xylene (also similar disubstituted benzene derivatives) can be efficiently separated with an elution sequence inversed with those for conventional mechanisms. More importantly, the separation mechanism is comprehensively and quantitatively visualized by single-crystal X-ray crystallography coupled with multiple computational simulation methods, in which the small apertures not only fit best the smallest para-isomer like molecular sieves, but also show seemingly trivial yet crucial structural alterations to distinguish the meta- and ortho-isomers via a gating mechanism, while the large channels allow fast guest diffusion and enable the structural/energetic effects to be accumulated in the macroscopic level.

No MeSH data available.


Related in: MedlinePlus

Experimental and simulated host-guest structures.a–c. Perspective views of local structures of the preferential adsorption site (drawn in stick mode; Zn purple, C dark gray, H light gray, N blue, O red) loaded with oX, mX and pX (hydrogen atoms are omitted for clarity) observed by single-crystal X-ray diffraction (Ortep plot in green, probability drawn at 30%), GCMC simulation (ball-and-stick mode in dark blue) and GCMC-PDFT calculation (ball-and-stick mode in orange). From left to right, the structures are projected along a common direction (same as that for Fig. 1), perpendicular to the aperture plane, parallel to the Zn· · ·Zn diagonal, and parallel to the imidazole· · ·imidazole diagonal, respectively.
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f3: Experimental and simulated host-guest structures.a–c. Perspective views of local structures of the preferential adsorption site (drawn in stick mode; Zn purple, C dark gray, H light gray, N blue, O red) loaded with oX, mX and pX (hydrogen atoms are omitted for clarity) observed by single-crystal X-ray diffraction (Ortep plot in green, probability drawn at 30%), GCMC simulation (ball-and-stick mode in dark blue) and GCMC-PDFT calculation (ball-and-stick mode in orange). From left to right, the structures are projected along a common direction (same as that for Fig. 1), perpendicular to the aperture plane, parallel to the Zn· · ·Zn diagonal, and parallel to the imidazole· · ·imidazole diagonal, respectively.

Mentions: The unit-cell volumes of 1∙oX and 1∙mX are very similar with that of 1∙g, while that of 1∙pX is similar with that of 1 (Table S1), indicating that the host framework can distort differently toward interaction with different guests. Structural analyses revealed that the oX, mX, and pX molecules locate quite differently in 1. In the large 1D channel, the xylene molecules show serious disorder, indicating weak host-guest interactions and large guest mobility, which indicate that the large channel mainly serves as the guest transportation path rather than the primary adsorption site. Inside and/or very close to the small aperture, the xylene molecules can be anisotropically refined without any restriction, confirming that the small aperture is the primary adsorption site for GC separation (Fig. 3 and S13–S15). The very different thermal parameters of oX, mX, and pX indicate that the host-guest binding strength follow 1∙pX > 1∙oX > 1∙mX, which is not completely consistent with the trend of adsorption enthalpies observed in the GC separation. Therefore, the energy consumptions of the structure alterations of the host framework should be also taken into account.


Structural, energetic, and dynamic insights into the abnormal xylene separation behavior of hierarchical porous crystal.

Lin JM, He CT, Liao PQ, Lin RB, Zhang JP - Sci Rep (2015)

Experimental and simulated host-guest structures.a–c. Perspective views of local structures of the preferential adsorption site (drawn in stick mode; Zn purple, C dark gray, H light gray, N blue, O red) loaded with oX, mX and pX (hydrogen atoms are omitted for clarity) observed by single-crystal X-ray diffraction (Ortep plot in green, probability drawn at 30%), GCMC simulation (ball-and-stick mode in dark blue) and GCMC-PDFT calculation (ball-and-stick mode in orange). From left to right, the structures are projected along a common direction (same as that for Fig. 1), perpendicular to the aperture plane, parallel to the Zn· · ·Zn diagonal, and parallel to the imidazole· · ·imidazole diagonal, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4481377&req=5

f3: Experimental and simulated host-guest structures.a–c. Perspective views of local structures of the preferential adsorption site (drawn in stick mode; Zn purple, C dark gray, H light gray, N blue, O red) loaded with oX, mX and pX (hydrogen atoms are omitted for clarity) observed by single-crystal X-ray diffraction (Ortep plot in green, probability drawn at 30%), GCMC simulation (ball-and-stick mode in dark blue) and GCMC-PDFT calculation (ball-and-stick mode in orange). From left to right, the structures are projected along a common direction (same as that for Fig. 1), perpendicular to the aperture plane, parallel to the Zn· · ·Zn diagonal, and parallel to the imidazole· · ·imidazole diagonal, respectively.
Mentions: The unit-cell volumes of 1∙oX and 1∙mX are very similar with that of 1∙g, while that of 1∙pX is similar with that of 1 (Table S1), indicating that the host framework can distort differently toward interaction with different guests. Structural analyses revealed that the oX, mX, and pX molecules locate quite differently in 1. In the large 1D channel, the xylene molecules show serious disorder, indicating weak host-guest interactions and large guest mobility, which indicate that the large channel mainly serves as the guest transportation path rather than the primary adsorption site. Inside and/or very close to the small aperture, the xylene molecules can be anisotropically refined without any restriction, confirming that the small aperture is the primary adsorption site for GC separation (Fig. 3 and S13–S15). The very different thermal parameters of oX, mX, and pX indicate that the host-guest binding strength follow 1∙pX > 1∙oX > 1∙mX, which is not completely consistent with the trend of adsorption enthalpies observed in the GC separation. Therefore, the energy consumptions of the structure alterations of the host framework should be also taken into account.

Bottom Line: Separation of highly similar molecules and understanding the underlying mechanism are of paramount theoretical and practical importance, but visualization of the host-guest structure, energy, or dynamism is very difficult and many details have been overlooked.Here, we report a new porous coordination polymer featuring hierarchical porosity and delicate flexibility, in which the three structural isomers of xylene (also similar disubstituted benzene derivatives) can be efficiently separated with an elution sequence inversed with those for conventional mechanisms.More importantly, the separation mechanism is comprehensively and quantitatively visualized by single-crystal X-ray crystallography coupled with multiple computational simulation methods, in which the small apertures not only fit best the smallest para-isomer like molecular sieves, but also show seemingly trivial yet crucial structural alterations to distinguish the meta- and ortho-isomers via a gating mechanism, while the large channels allow fast guest diffusion and enable the structural/energetic effects to be accumulated in the macroscopic level.

View Article: PubMed Central - PubMed

Affiliation: MOE Key Laboratory of Bioinorganic and Synthetic Chemistry, School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou 510275, P.R. China.

ABSTRACT
Separation of highly similar molecules and understanding the underlying mechanism are of paramount theoretical and practical importance, but visualization of the host-guest structure, energy, or dynamism is very difficult and many details have been overlooked. Here, we report a new porous coordination polymer featuring hierarchical porosity and delicate flexibility, in which the three structural isomers of xylene (also similar disubstituted benzene derivatives) can be efficiently separated with an elution sequence inversed with those for conventional mechanisms. More importantly, the separation mechanism is comprehensively and quantitatively visualized by single-crystal X-ray crystallography coupled with multiple computational simulation methods, in which the small apertures not only fit best the smallest para-isomer like molecular sieves, but also show seemingly trivial yet crucial structural alterations to distinguish the meta- and ortho-isomers via a gating mechanism, while the large channels allow fast guest diffusion and enable the structural/energetic effects to be accumulated in the macroscopic level.

No MeSH data available.


Related in: MedlinePlus