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A particular salt crystal can release liquid when compressed, then take it back when the pressure is removed. Researchers call it a “solvate sponge crystal”: its starting form, (DMF)3NaClO4, loses one equivalent of the solvent N,N-dimethylformamide (DMF) under pressure and becomes (DMF)2NaClO4. The change can reverse, and heating and cooling also drive the transformation.
What happens when the crystal is squeezed?
The 2021 study describes a specific solvated inorganic salt—not a general property of ordinary crystals. In the starting phase, three DMF molecules are associated with each sodium perchlorate formula unit. Pressure prompts the crystal to release one DMF equivalent and convert to a lower-solvate phase with two DMF molecules per formula unit.
When pressure is removed, the lower-solvate crystal reabsorbs DMF and returns to the 3:1 phase. Heating and cooling can also induce a reversible transformation. The reported process is therefore a change between two solvates, rather than simply melting and resolidifying: the material releases and takes up solvent as its crystal structure changes. This contrasts with crystals that melt without losing solvent or melt while decomposing and fail to recover.
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How the two crystal phases differ
| Feature | Starting phase | Lower-solvate phase |
|---|---|---|
| Composition | (DMF)3NaClO4 | (DMF)2NaClO4 |
| Crystal form | Hexagonal | Monoclinic |
| DMF content | Three DMF equivalents per sodium perchlorate formula unit | Two DMF equivalents per sodium perchlorate formula unit |
| Reported molar volume | Reference phase | 27% lower than the starting phase, according to Chemistry World’s account of the 2021 study |
The 27% figure applies to the comparison between these two phases of this material; it should not be generalized to other crystals or solvates.
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Why pressure direction matters
The report describes different structural responses depending on the direction of applied pressure in the crystal’s x, y, and z directions:
- Pressure in the x and y directions: The crystal deforms slightly. Perchlorate ions move into positions previously occupied by sodium ions, and DMF is expelled at the crystal’s side, leaving a thin surface layer.
- Pressure in the z direction: Some sodium–DMF contacts break and sodium–perchlorate contacts form. This change accompanies conversion to the monoclinic 2:1 solvate phase.
What could the material be used for?
The researchers discussed possible applications, but the 2021 report does not establish a finished product or a deployed battery. Jagadese Vittal of the National University of Singapore said the work could open an avenue for melt-castable crystalline materials. Prabhat Prakash of the Indian Institute of Science Education and Research in Pune described battery research as a direction the team was exploring: the crystal has sodium-ion channels with sufficiently small energy barriers for conduction, but DMF and perchlorate can both be reduced at a typical battery anode. The team’s stated plan was to seek crystals with more redox-stable components.
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Those comments describe research possibilities, not demonstrated commercial uses. The report does not present the crystal as a consumer product or show that it has been used in a working battery.
What is established—and what remains unclear
Chemistry World’s 2021 account cites the study by Prakash and colleagues in Chemical Science, volume 12, page 5574, DOI 10.1039/d0sc06455f. The account supports the composition change, reversible response, directional effects, and reported phase-volume difference described here. It does not provide exact pressure or temperature thresholds, so those conditions cannot be specified from that account. It also does not establish later commercialization or a deployed application.
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