Inelastic Neutron Scattering and Theoretical Studies of H2 Sorption in a Dy(III)-Based Phosphine Coordination Material

Katherine A. Forrest, Tony Pham, Peter A. Georgiev, Jan Peter Embs, Nolan W. Waggoner, Adam Hogan, Simon M. Humphrey, Juergen Eckert, Brian Space

Research output: Contribution to journalArticle

7 Scopus citations

Abstract

A combined inelastic neutron scattering (INS) and theoretical study of H2 sorption was performed in PCM-16, a phosphine coordination material (PCM) with the empirical formula [(CH3)2NH2][Dy2(tctpo)2(O2CH)] (tctpo = tris(p-carboxylato)triphenylphosphine oxide). INS measurements at different loadings of H2 revealed a peak occurring at low rotational tunnelling energies (ca. 5-8 meV), which corresponds to a high barrier to rotation and, therefore, a strong interaction with the host. Molecular simulations of H2 sorption in PCM-16 revealed that the H2 molecules sorbed at two main sites in the material: (1) the (CH3)2NH2+ counterions and (2) within the small pores of the framework. Two-dimensional quantum rotation calculations revealed that the peak occurring from approximately 5-8 meV in the INS spectra for PCM-16 is associated with sorption onto the (CH3)2NH2+ ions. These counterions provide for the strongest H2 sorption sites in the material, which corresponds to an isosteric heat of adsorption (Qst) value of close to 8 kJ mol-1. The calculated rotational barrier for the (CH3)2NH2+-H2 interaction in PCM-16 (45.60 meV) is higher than those for a number of extant metal-organic frameworks (MOFs), especially those that contain open-metal sites. This study provides insights into the H2 sorption mechanism in a PCM for the first time and shows how the inclusion of counterions in porous materials is a promising method to increase the H2 sorption energetics in such materials.

Original languageEnglish
Pages (from-to)7619-7626
Number of pages8
JournalChemistry of Materials
Volume27
Issue number22
DOIs
StatePublished - Oct 22 2015

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