Solvent Templating and Structural Dynamics of Fluorinated 2D Cu-Carboxylate MOFs Derived from the Diffusion-Controlled Process

Michał K Leszczyński,Krzysztof Gontarczyk,Janusz Lewiński,Iwona Justyniak

doi:10.1021/acs.inorgchem.9b03472

Michał K Leszczyński, Krzysztof Gontarczyk + Show 2 more

Open Access

https://doi.org/10.1021/acs.inorgchem.9b03472

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Abstract

The layered 2D MOFs, owing to their enhanced flexibility and tunability, have recently emerged as a promising alternative to the 3D microporous MOFs in the quest for novel responsive functional materials. However, maintaining the simultaneous control over self-assembly of molecular building blocks as well as ordered stacking of MOF layers poses a significant synthetic challenge. We report on the controlled 2D MOF formation based on a case study of solvent-templated growth of a series of 2D Cu(II)–carboxylate MOFs varying in stacking modes and distances using a diffusion-controlled MOF deposition approach in various solvent mixtures. Moreover, we demonstrate the structural dynamics of the developed 2D MOFs involving both in-plane and out-of-plane movements of the individual 2D layers triggered by solvent exchange, which allowed for selective postsynthetic transformations between the developed 2D MOFs. We also investigated the gas adsorption properties of the developed MOFs, which demonstrates a remarkable crystal size effect on the N2 adsorption capacity using a model 2D MOF system.

Highlights

Metal−organic frameworks (MOFs) composed of organic linkers and inorganic nodes have been attracting the immense attention of researchers due to their diverse and strikingly robust architectures combined with high surface areas and great chemical diversity
Reactions involving water/alcohol mixtures resulted in the formation of four new 2D MOF materials: [Cu(hfipbb)·MeOH]I‐xy (2; prepared in H2O/MeOH), [Cu(hfipbb)·EtOH]I‐xy (3; H2O/EtOH), [Cu(hfipbb)·iPrOH]I‐xy (4; H2O/iPrOH), and [[Cu(hfipbb)· H2O]·tBuOH]I‐xy (5; H2O/tBuOH) (Figure 3), all isolated in a form of turquoise flake-shaped single crystals
The resulting materials were characterized by elemental analysis, PXRD and single-crystal X-ray diffraction (SCXRD), FTIR spectroscopy, and a gas adsorption study involving N2, H2, and CO2 as adsorbates

Summary

■ INTRODUCTION

Metal−organic frameworks (MOFs) composed of organic linkers and inorganic nodes have been attracting the immense attention of researchers due to their diverse and strikingly robust architectures combined with high surface areas and great chemical diversity. The literature data includes four examples of Cu(hfipbb) structures, all prepared in solvothermal conditions, which differ in internal structure of the networks, interpenetration, as well as layer stacking distance and geometry, which results from varying preparation conditions (Figure 2).[38−41] Similar variations have been observed for other 2D MOF systems, which indicates that their supramolecular structure can be influenced by various subtle effects like solvent type, temperature, pH, additives, etc.[14,15]. Synthesis of flakeshaped single crystals of 2 was performed by the same procedure as for 1 with exception that H2O/MeOH mixture (1:1 by volume) was used instead of H2O. Synthesis of flake-shaped single crystals of 3 was performed by the same procedure as for 1 with the exception that an H2O/EtOH mixture (1:1 by volume) was used instead of H2O. Synthesis of flake-shaped single crystals of 5 was performed by the same procedure as for 1 with the exception that an H2O/tBuOH mixture (1:1 by volume) was used instead of H2O.

■ RESULTS AND DISCUSSION

■ CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES