In the news this week is a report of a molecule whose crystal lattice is capable of both storing and releasing large amounts of hydrogen gas at modest pressures and temperatures. Thus “NU-1501-Al” can absorb 14 weight% of hydrogen. To power a low-polluting car with a 500 km range, about 4-5 kg of hydrogen gas would be need to be stored and released safely. The molecule is of interest since it opens a systematic strategy of synthetically driven optimisation towards a viable ultra-porous storage material,[1] much like a lead drug compound can be optimised.
I thought it would be informative to show a 3D interactive model of the crystal lattice here and so I went in search of coordinates. These are indeed available online. This is an example of scientific data Interoperability and Reuse, part of the FAIR data acronym. Before showing the model, I thought it worth briefly describing the procedure for starting with deposited data and converting (interoperating) it to the model here.
Clearly, the hexagonal cavities formed can accommodate a large number of hydrogen molecules. As to why, it is no doubt complex, but I cannot help but notice that the surface of the cavity is lined with multiple C-H units from the aryl spacer units pointing inwards. Given that hydrogen is a very good inducer of dispersion attractions, it would be interesting indeed to see whether the very large number of H…H2 dispersion attractions possible inside the cavity of this species might at least in part be responsible for the ability of this framework to accommodate hydrogen (or methane) gas.[2] It would be good to have an estimate of the dispersion energy term for NU-1501-Al and related species and the contribution of this term to the overall thermodynamics of the system. By the same token, replacing the four aryl C-H units with C-F units (a weaker dispersion attractor, think non-stick teflon) should reduce the ability to absorb hydrogen if dispersion is indeed important.
‡On the other hand, if the orientation of the aryl C-H groups is important in terms of dispersion attractons, perhaps these groups are actually critical to the effect.
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I find that when I scroll the page using two fingers on my Mac touchpad that it will annoyingly resize the image when the pointer gets to the embedded image. Shrink it to a pint scrolling down, and vv going up. Not just with jsmol, as here, but often with things like Google maps too. But not on all pages with such scalable images, which suggests that there is a setting somewhere for authors to prevent this behaviour.
Maybe it's an Apple laptop/touchpad thing and as such isn't often reported??