Fig. 4 Hydrogen-bonded motifs in stepanovite and zhemchuzhnikovite and reversibility of thermal dehydration of zhemchuzhnikovite. Hydrogen-bonded motifs in stepanovite and zhemchuzhnikovite and reversibility of thermal dehydration of zhemchuzhnikovite. (A) The 3D hydrogen-bonded network of Mg(H2O)62+ ions and interlayer water molecules in stepanovite. (B) Three parallel hydrogen-bonded columns of Mg(H2O)62+ ions and interlayer water molecules in zhemchuzhnikovite, each propagating through a channel formed by the overlap of hcb layers. For clarity, the metal-organic hcb layers are omitted. (C) The reversibility of structural changes upon dehydration and rehydration of synthetic zhemchuzhnikovite is demonstrated by comparison of PXRD patterns (top to bottom): simulated zhemchuzhnikovite NaMgFe0.41Al0.59(ox)3⋅9H2O; simulated for stepanovite NaMgFe(ox)3⋅9H2O; and zhemchuzhnikovite after one, two, and three cycles of thermal dehydration at 90°C and rehydration by exposure to 100% relative humidity (RH) at room temperature. Igor Huskić et al. Sci Adv 2016;2:e1600621 Copyright © 2016, The Authors