The rotational dynamics of H₂ adsorbed in covalent organic frameworks

Abstract

A combined inelastic neutron scattering (INS) and theoretical study was carried out on H adsorbed in two covalent organic framework (COF) materials: COF-1 and COF-102. These COFs are synthesized from self-condensation reactions of 1,4-benzenediboronic acid (BDBA) and tetra(4-(dihydroxy)borylphenyl)methane (TBPM) molecules, respectively. Molecular simulations of H adsorption in COF-1 revealed that the H molecules occupy the region between two eclipsed layers of the COF. The most favorable H binding site in COF-1 is located between two BO clusters of the eclipsed layers. Two distinct H binding sites were identified in COF-102 from the simulations: the BO clusters and the phenyl rings of the tetraphenylmethyl units. Two-dimensional quantum rotation calculations for H adsorbed at the considered sites in both COFs resulted in rotational transitions that are in good agreement with those that appear in the corresponding INS spectra. Such calculations were important for interpreting the INS spectra in these materials. Calculation of the rotational potential energy surface for H bound at the most favorable adsorption site in COF-1 and COF-102 revealed unusually high rotational barriers that are attributed to the nature of the BO rings. The values for these barriers to rotation are greater than or comparable to those observed in some metal-organic frameworks (MOFs) that possess open-metal sites. This study demonstrates the power of using INS experiments in conjunction with theoretical calculations to gain valuable insights into the nature of the binding sites and, for the first time, the rotational dynamics of H adsorbed in COFs.

An assessment of strategies for the development of solid-state adsorbents for vehicular hydrogen storage

“…For example, successful simulation of spectroscopic probes of H 2 rotational motion in MOFs and COFs requires explicit solutions of quantum equations for the five relevant degrees of freedom. 109,110 Inclusion of delocalized quantum nuclear motion is likewise critical in order to reliably simulate H 2 binding and obtain uptake curves with quantitative accuracy.…”

Dynamics & Spectroscopy with Neutrons—Recent Developments & Emerging Opportunities

“…Developments in gas-handling systems have also paved the way to probe gate-opening and related network-breathing phenomena arising from the unique elastic properties of MOFs—see entries in Table 1 and Refs. [ 151 , 266 , 267 , 268 , 269 , 270 , 271 , 272 , 273 , 274 , 275 , 276 , 277 , 278 , 279 , 280 , 281 , 282 , 283 , 284 , 285 , 286 , 287 , 288 , 289 , 290 ].…”

MPMC and MCMD: Free High‐Performance Simulation Software for Atomistic Systems

“…This indicates that such INS features can be attributed to H 2 localized at these particular binding sites in MOF‐5. Overall, our group has successfully utilized MPMC to calculate the rotational transitions for H 2 adsorbed at different binding sites in numerous porous materials …”

“…Our aim with MPMC and MCMD is to leverage the best hardware available to date, increase the physical accuracy of traditional force field modeling through the inclusion of explicit, long‐range many‐body polarization in both the energetics and forces. We have used both codes in many published theoretical studies but have not formally introduced them until now.…”