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Confinement of Iodine Molecules into Triple-Helical Chains within Robust Metal–Organic Frameworks
journal contribution
posted on 2017-10-11, 00:00 authored by Xinran Zhang, Ivan da Silva, Harry G. W. Godfrey, Samantha K. Callear, Sergey A. Sapchenko, Yongqiang Cheng, Inigo Vitórica-Yrezábal, Mark D. Frogley, Gianfelice Cinque, Chiu C. Tang, Carlotta Giacobbe, Catherine Dejoie, Svemir Rudić, Anibal J. Ramirez-Cuesta, Melissa A. Denecke, Sihai Yang, Martin SchröderDuring nuclear waste
disposal process, radioactive iodine as a
fission product can be released. The widespread implementation of
sustainable nuclear energy thus requires the development of efficient
iodine stores that have simultaneously high capacity, stability and
more importantly, storage density (and hence minimized system volume).
Here, we report high I2 adsorption in a series of robust
porous metal–organic materials, MFM-300(M) (M = Al, Sc, Fe,
In). MFM-300(Sc) exhibits fully reversible I2 uptake of
1.54 g g–1, and its structure remains completely
unperturbed upon inclusion/removal of I2. Direct observation
and quantification of the adsorption, binding domains and dynamics
of guest I2 molecules within these hosts have been achieved
using XPS, TGA-MS, high resolution synchrotron X-ray diffraction,
pair distribution function analysis, Raman, terahertz and neutron
spectroscopy, coupled with density functional theory modeling. These
complementary techniques reveal a comprehensive understanding of the
host–I2 and I2–I2 binding
interactions at a molecular level. The initial binding site of I2 in MFM-300(Sc), I2I, is located near
the bridging hydroxyl group of the [ScO4(OH)2] moiety [I2I···H–O =
2.263(9) Å] with an occupancy of 0.268. I2II is located interstitially between two phenyl rings of neighboring
ligand molecules [I2II···phenyl
ring = 3.378(9) and 4.228(5) Å]. I2II is
4.565(2) Å from the hydroxyl group with an occupancy of 0.208.
Significantly, at high I2 loading an unprecedented self-aggregation
of I2 molecules into triple-helical chains within the confined
nanovoids has been observed at crystallographic resolution, leading
to a highly efficient packing of I2 molecules with an exceptional
I2 storage density of 3.08 g cm–3 in
MFM-300(Sc).