Some crystal structures are only there if you look at the right temperature. A new study led by EPFL, with ELDICO co-authors, reports a layered copper selenite, (NH3)2Cu5(SeO3)2(OH)6, whose water content sets the spacing between its layers. Three closely related forms exist, tuned by hydration – and each needed a different route to a structure.
One form grew crystals large enough for single-crystal X-ray diffraction. The other two did not: the crystals stayed far below the size X-ray methods need. Those forms were resolved by 3D electron diffraction (3D ED), which works on individual crystals in the sub-micrometre range – the nanogram-sized grains that fall through the cracks of conventional single-crystal work.
The fully hydrated form added a second constraint. It is only stable under the measurement conditions (high vacuum, electron exposure) at low temperature. Capturing it meant keeping the sample cold from preparation through measurement – cryo transfer onto the ELDICO ED-1 and data collection under cryogenic conditions. Without that, the structure would simply not have been there to measure.
Cryo capability has been part of how ELDICO works for a long time. It is not usually the headline. Here it was the difference between seeing a structure and missing it, and between a partial picture of the hydration series and a complete one.
Why it matters for solid-form work
Hydrates, solvates and metastable forms are a familiar problem in pharmaceutical and materials development: the form that appears under one set of conditions may not survive isolation, and the crystals it gives are often too small for X-ray. 3D ED removes the "grow a bigger crystal" bottleneck, and cryo handling extends that to forms that exist only under controlled conditions. If your open question is a form you can make but cannot characterise, this study is a concrete example of what the combination delivers.
The paper, Hydration-controlled layer stacking in (NH3)2Cu5(SeO3)2(OH)6, appears in Inorganic Chemistry 65, 19849 (2026), doi:10.1021/acs.inorgchem.6c02535; an open-access preprint is on arXiv. See all ELDICO publications.