(192ah) Density Functional Theory Screening of Metal Catecholates for Adsorption of Toxic Pnictogen Hydride Gases

Ammonia (NH₃), phosphine (PH₃), and arsine (AsH₃) are toxic gases that are commonly used in industry, which places workers at risk of accidental exposure. Most widely used filtration methods rely on activated carbon, which has low capacity and selectivity for these gases. However, in recent years, researchers have looked to other porous materials, such as metal-organic frameworks (MOFs), as sorbents for toxic gases. [1] One benefit of using MOFs is they can be tailored to specific adsorption applications by adding functional groups or metal sites which increase the MOF’s affinity for the target molecules. [2]

We used density functional theory to study interactions between ammonia, phosphine, arsine, and 33 metal catecholates in order to examine periodic trends in the binding strength between the gases and metals. We find markedly different behavior in ammonia than in phosphine and arsine due to different processes governing the adsorption, despite the apparent similarity of these molecules. Phosphine and arsine adsorption is primarily driven by electron density being donated from the adsorbate molecule to the metal atom, while ammonia binding involves both some electron donation and a significant Coulombic attraction between the negatively-charged N atom and the positively-charged metal atom.

 We will discuss how these different adsorption mechanisms are manifested through trends in binding strength across the periodic table, as well as the implications for adsorption of ammonia and phosphine in humid environments.

1. N. S. Bobbitt, M. L. Mendonca, A. J. Howarth, T. Islamoglu, J. T. Hupp, O. K. Farha, R. Q. Snurr, "Metal–organic frameworks for the removal of toxic industrial chemicals and chemical warfare agents." Chemical Society Reviews, in press.
2. D. Yu, P.Ghosh, and R. Q. Snurr, “Hierarchical modeling of ammonia adsorption in functionalized metal–organic frameworks.” Dalton Transactions, 41(14), 3962-3973 (2012)