Polymorphism of Magnesium Chloride Decahydrate under High Pressures and Low Temperatures Found in Icy Moons

Magnesium
chloride hydrates show a rich diversity of structural
forms, with different hydration numbers ranging from 1 to 12. We show
that this structural versatility is also present within the same hydration
numbers, with the formation of a new phase of magnesium chloride decahydrate
(MgCl2·10H2O-II) stable at the conditions
of 0.03–0.40(14) GPa at 234(11) K and up to 2.11(3) GPa at
220(2) K, as determined by in situ single-crystal X-ray diffraction.
The hydrogen bonding interactions of MgCl2·10H2O-II are identified and the bulk modulus determined at B0 = 18.9(12) GPa at 220(2) K. We discuss the
implication of this high-pressure MgCl2 hydrate for icy
moon compositional investigations and showcase the structural and
density changes between the various hydrates in MgCl2·nH2O.