The importance of charge–quadrupole interactions for H₂ adsorption and diffusion in CuBTC

Abstract

We have assessed the effects of charge–quadrupole interactions (CQIs) between the framework atoms of copper(II) benzene-1,3,5-tricarboxylate (CuBTC) and adsorbed H₂ molecules on equilibrium adsorption properties and self- and transport diffusivities. We have also compared charges computed from periodic density functional theory (DFT) on the fully periodic CuBTC structure with charges derived from DFT calculations on cluster models of CuBTC. Our results indicate that carboxylate group atom charges computed from plane wave periodic DFT with the Bader charge analysis formalism are not consistent with the charges computed from the ChelpG method from Gaussian-based DFT cluster calculations. The charges derived from Bader analysis seem to be too large. Adsorption isotherms computed from Monte Carlo simulations and diffusivities computed from molecular dynamics simulations indicate that CQIs have a substantial impact on equilibrium and transport properties of H₂ adsorbed in CuBTC at 77 K. Conversely, both adsorption isotherms and diffusivities were shown to be essentially unaffected by CQIs at 298 K.

Keywords:

• charge–quadrupole interactions
• CuBTC
• H₂ adsorption
• H₂ diffusion
• MOF

Acknowledgements

We thank Anant Kulkarni and Yang Wang for their helpful discussions. Funding for this work has been provided by the U.S. Department of Energy through the National Energy Technology Laboratory under grant No. 41817M203841817M2000.