Prediction of Multiple Hydrogen Ligation at a Vanadium(II) Site in a Metal–Organic Framework

Densifying hydrogen in a metal–organic framework
(MOF) at
moderate pressures can circumvent challenges associated with high-pressure
compression. The highly tunable structural and chemical composition
in MOFs affords vast possibilities to optimize binding interactions.
At the heart of this search are the nanoscale characteristics of molecular
adsorption at the binding site(s). Using density functional theory
(DFT) to model binding interactions of hydrogen to the exposed metal
site of cation-exchanged MFU-4l, we predict multiple
hydrogen ligation of H2 at the first coordination sphere
of V(II) in V(II)-exchanged MFU-4l. We find that
the strength of this binding between the metal site and H2 molecules can be tuned by altering the halide counterion adjacent
to the metal site and that the fluoride containing node affords the
most favorable interactions for high-density H2 storage.
Using energy decomposition analysis, we delineate electronic contributions
that enable multiple hydrogen ligation and demonstrate its benefits
for hydrogen adsorption and release at modest pressures.