2025 AIChE Annual Meeting

(188g) Analyzing the Vibrational Spectra of ZIF-L Using First-Principles Molecular Simulations

Authors

Andrea Kraetz, Johns Hopkins University
Yurun Miao, Johns Hopkins University
Roshan Ashokbhai Patel, University of Minnesota
Pragya Parihar, University of Minnesota, Twin Cities
Kayley Waltz, Johns Hopkins University
Mueed Ahmad, Brookhaven National Laboratory
Anibal Boscoboinik, Brookhaven National Laboratory
Samuel Tenney, Brookhaven National Lab
Michael Tsapatsis, Johns Hopkins University
J. Ilja Siepmann, University of Minnesota-Twin Cities
Metal-organic frameworks (MOFs) are crystalline porous materials with metal nodes and organic linkers as building units. Among MOFs, zeolitic imidazolate frameworks (ZIFs) are a subset with tetrahedral building units of metal nodes coordinated with imidazolate ligand. ZIF-L, a type of ZIF, is a 2D crystal structure that contains zinc cations coordinated with 2-methylimidazole (2mIm) ligands.1 ZIF-L membranes can be utilized for applications such as gas separation and sensing.2

Previously, we conducted a detailed investigation on the vibrational modes of ZIF-8, which consist of a single type of 2mIm linker, i.e., μ-bridged 2mIm.3 Although ZIF-L has the same building blocks as ZIF-8, ZIF-L has three variations of 2mIm linkers/ligands, μ-bridged 2mIm, dangling 2mIm (2mImD), and free 2mIm linker (2mImF). These varieties of linkers should contribute to unique vibrational modes in the IR spectra. Also, the concentration of 2mImF linkers in the ZIF-L structure is unknown. To address this, we conducted geometry optimization using density functional theory (DFT) for periodic ZIF-L unit cells with varying numbers of 2mImF linkers and confirmed the possibility of accommodating a maximum of eight 2mImF in a ZIF-L unit cell. Further, we performed first-principles molecular dynamics (FPMD) of ZIF-L with varying numbers of 2mImF at T = 298 K and frequency calculations for the DFT-optimized structures to obtain infrared (IR) spectra. Comparison with ZIF-8 spectra allows us to identify the unique vibrational modes of ZIF-L which are found to be associated with the 2mImD and 2mImF ligands. Additionally, we compared the line spectra for ZIF-L without and with 2mImF ligands, identifying the distinct peaks for 2mImF ligands.

References

  1. Chen, R., Yao, J., Gu, Q., Smeets, S., Baerlocher, C., Gu, H., Zhu, D., Morris, W., Yaghi, O. M., & Wang, H. (2013). A two-dimensional zeolitic imidazolate framework with a cushion-shaped cavity for CO2 Chem. Commun., 49, 9500–9502.
  2. Wang, S., Liu, J., Pulido, B., Li, Y., Mahalingam, D., & Nunes, S. P. (2020). Oriented Zeolitic Imidazolate Framework (ZIF) Nanocrystal Films for Molecular Separation Membranes. ACS Appl. Nano Mater., 3, 3839–3846.
  3. Ahmad, M.; Patel, R.; Lee, D. T.; Corkery, P.; Kraetz, A.; Prerna; Tenney, S. A.; Nykypanchuk, D.; Tong, X.; Siepmann, J. I.; Tsapatsis, M.; Boscoboinik, J. A. ZIF-8 Vibrational Spectra: Peak Assignments and Defect Signals. (2024). ACS Appl. Mater. Interfaces., 16, 27887–27897.