The Crystal Structures of two Anhydrous Magnesium Hydroxychloride Phases from in situ Synchrotron Powder Diffraction Data

The crystal structures of two members of the solid solution series Mg(OH)xCly x+y = 2, Mg(OH)1.7Cl0.3 (P3̃ m1, a = 3.169(2) Å, c = 5.530(12), V = 48.1(1) Å3 at T = 365 °C) and MgOHCl (R3̃ m, a = 3.3877(4) Å, c = 17.534(4) Å, V = 174.27(6) Å3 at T = 625 °C) were determined from in situ synchrotron powder diffraction data at high temperature upon dehydration of 3Mg(OH)2·MgCl2·8H2O (F3) and 5Mg(OH)2·MgCl2·8H2O (F5) phases. The crystal structures of Mg(OH)1.7Cl0.3 (example of ss‐type‐OH) and MgOHCl (example of ss‐type‐Cl) can be related to the C19 (CdCl2) and C6 (CdI2) structure type, respectively, with the disordered chloride and hydroxide anions occupying the same crystallographic site in layers.