Some crystal structures only appear 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, each 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. Their crystals stayed far below the size X-ray methods need, so 3D electron diffraction (3D ED) resolved them instead, working on individual crystals in the sub-micrometre range.
The fully hydrated form added a second constraint. It is only stable at low temperature under the measurement conditions of high vacuum and electron exposure. Capturing it meant keeping the sample cold from preparation through measurement: cryo transfer onto the ELDICO ED-1, with data collected under cryogenic conditions. Warm it up and the structure is no longer there to measure.
Cryo has been part of how ELDICO works for a long time. On most samples it stays in the background. Here it was the difference between solving the 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 recurring 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 need to grow a bigger crystal, and cryo handling extends that to forms that only exist under controlled conditions.
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.