Dehydration of Magnesium Bromide Hexahydrate Studied by in situ X‐ray Powder Diffraction

Abstract

Laboratory X-ray powder diffraction data were used to investigate the dehydration process of magnesium bromide hexahydrate in the temperature range 300 K Յ T Յ 420 K. By heating of the as synthesized hexahydrate (MgBr 2 ·6H 2 O, observed in the temperature range 300 K Յ T Յ 349 K), three lower hydrates can be obtained in overlapped temperature regions:Although the crystal structure of the hexahydrate was published almost eighty years ago, there are no data on the structures of the lower hydrates. The crystal structures are reported and are found to be isotypical with the structures of the respective chlorides. The 59 structure of MgBr 2 ·6H 2 O is characterized by discrete Mg(H 2 O) 6 octahedra and is the only hydrate of this group that contains unbonded Branions. MgBr 2 ·4H 2 O is composed of discrete MgBr 2 (H 2 O) 4 octahedra, and the structure was found to be disordered. The crystal structure of MgBr 2 ·2H 2 O is formed by single chains of edge-sharing MgBr 4 (H 2 O) 2 octahedra, while in the case of MgBr 2 ·H 2 O double chains of edgeshared MgBr 5 H 2 O are formed. By increasing the temperature, as expected, positive thermal expansion was evidenced. Thermal expansion coefficients, based on the changes of the unit cell parameters, were derived for the following hydrates: MgBr 2 ·6H 2 O, MgBr 2 ·4H 2 O, and MgBr 2 ·2H 2 O.

Synthesis and Characterization of the Manganese Hydroxide Halides Mn(OH)X (X = Br, I) and Crystal Structure of trans‐MnBr2·4H2O

“…In contrast to the stable phase of manganese(II) bromide tetrahydrate described by Sudarsanan , where the bromine atoms are in cis configuration, the halide atoms of this modification occupy the axial positions, forming a trans configuration at the octahedron (Figure ). Trans ‐MnBr 2 · 4H 2 O crystallizes isotypically to the layered crystal structures of MgCl 2 · 4H 2 O and MgBr 2 · 4H 2 O examined by Dinnebier and his group , . A stacking fault along the b axis is manifested by the half occupation of every possible coordination polyhedron in each layer (Figure ).…”

Crystal structures of hydrates of simple inorganic salts. I. Water-rich magnesium halide hydrates MgCl2·8H2O, MgCl2·12H2O, MgBr2·6H2O, MgBr2·9H2O, MgI2·8H2O and MgI2·9H2O

“…Our redetermination also resulted in a description in the space group C2/m, with unit-cell parameters as given in Table 1 and the Supplementary materials. This can be compared with data from Agron & Busing (1985) and a structure analysis by Dinnebier et al (2013) published during the preparation of this manuscript. The molecular unit is shown in Fig.…”