author ="Franz, Douglas M. and Dyott, Zachary E. and Forrest, Katherine A. and Hogan, Adam and Pham, Tony and Space, Brian",
title  ="Simulations of hydrogen{,} carbon dioxide{,} and small hydrocarbon sorption in a nitrogen-rich rht-metal-organic framework",
journal  ="Phys. Chem. Chem. Phys.",
year  ="2018",
volume  ="20",
issue  ="3",
pages  ="1761-1777",
publisher  ="The Royal Society of Chemistry",
doi  ="10.1039/C7CP06885A",
url  ="http://dx.doi.org/10.1039/C7CP06885A",
abstract  ="Grand canonical Monte Carlo (GCMC) simulations of gas sorption were performed in Cu-TDPAH{,} also known as rht-MOF-9{,} hereafter [1]{,} a metal-organic framework (MOF) with rht topology consisting of Cu2+ ions coordinated to 2{,}5{,}8-tris(3{,}5-dicarboxyphenylamino)-1{,}3{,}4{,}6{,}7{,}9{,}9b-heptaazaphenalene (TDPAH) ligands. This MOF is notable for the presence of open-metal copper sites and high nitrogen content on the linkers. [1] Exhibits one of the highest experimental H2 uptakes at 77 K/1 atm within the extant rht-MOF family (ca. 2.72 wt%) and also has strong affinity for CO2 (5.83 mmol g-1 at 298 K/1 atm). Our simulations{,} which include explicit many-body polarization interactions{,} accurately modeled macroscopic thermodynamic properties (e.g.{,} sorption isotherms and isosteric heats of adsorption (Qst)) as well as the binding sites for H2{,} CO2{,} CH4{,} C2H2{,} C2H4{,} and C2H6 in the MOF. Four different binding sites were observed through analysis of the radial distribution function (g(r)) about the two chemically distinct Cu2+ ions{,} simulated annealing calculations{,} and examination of the three-dimensional histogram showing the sites of occupancy: (1) at the Cu2+ ion facing toward the center of the linker (CuL){,} (2) at the Cu2+ ion facing away from the center of linker (CuC){,} (3) nestled between three [Cu2(O2CR)4] units in the corner of the truncated tetrahedral (T-Td) cage and (4) straddling the copper nuclei parallel to the axis of the Cu-Cu bond within the T-Td cage. The low-loading (initial) binding site in the MOF is highly sensitive to the partial charges of the Cu2+ ions that were used for parametrization. It was discovered that most sorbates prefer to sorb onto or near the Cu2+ ions that exhibit the greater partial positive charge (i.e.{,} at site 1). The simulated H2 and CO2 sorption results obtained using a polarizable potential for the respective sorbates are in good agreement with the corresponding experimental data{,} especially near ambient pressure. Simulations of gas sorption were also performed in [1] using nonpolarizable potentials for the individual sorbates; these include potentials from the TraPPE force field for most sorbates."}