Crystal chemistry of MX · MgX₂ · 6H₂O type compounds

Abstract

The following MX · MgX2 · 6H2O compounds (double salt hexahydrates) were synthesized by variation of the M+ and X− ions: CsCl · MgCl2 · 6 H2O, Li(H2O)Cl · MgCl2 · 6H2O, NH4Br · MgBr2 · 6 H2O, RbBr · MgBr2 · 6 H2O, CsBr. MgBr2 · 6 H2O, KI · MgI2 · 6 H2O, NH4I. Mgl2 · 6 H2O and RbI · MgI2 · 6H2O. By X‐ray analysis of powder samples the lattice parameters and the space group were determined. On the basis of the results thus obtained, an identification with structural types was carried out. In accordance with the findings, the structure is made up of (M+)X6−octahedra which are linked into perovskite type units by sharing vertices. Their interstices are occupied by the Mg(H2O)62+ octahedra. A “tolerance factor” t which has been calculated on the basis of the proportion of radii and which attains values between 1.045 and 1.061 is a criterion for the upper limit of the area of existence of this structure. Carnallite has a higher to value and, therefore, a different structure.

Thermodynamic study of (b1LiBr +b2MgBr2)(aq), wherebdenotes molality, at the temperature 348.15K

“…(7)(8)(9) The only exception are the solutions with the participation of LiX. Lithium chlorocarnallite with the composition LiCl·MgCl 2 ·7H 2 O (1−1−7) crystallizes in (b 1 LiCl+b 2 MgCl 2 )(aq) from T=263.15 K to T=343.15 K. (10) The crystal structure of lithium chlorocarnallite is similar to all the remaining carnallites (with composition 1−1−6) consisting of two kinds of coordination polyhedra: {Mg(H 2 O) 6 } 2+ and {M + X 6 }. According to Emons et al, (6) (6) have predicted a perovskite-type structure of the lithium bromocarnallite, if it exists.…”

Discontinuities in the mixed-crystal series of isostructural carnallite-type double salts

“…(10,11) The only known exception is potassium chlorocarnallite which crystallizes in an orthorhombic crystal system. (12,13) Due to its different composition, lithium chlorocarnallite: Li(H 2 O)Cl·MgCl 2 ·6H 2 O, crystallizes in space group C2/m.…”

“…(12,13) Due to its different composition, lithium chlorocarnallite: Li(H 2 O)Cl·MgCl 2 ·6H 2 O, crystallizes in space group C2/m. (10) The investigation of the co-crystallization of chlorocarnallites, bromocarnallites, and iodocarnallites is very interesting with a view to elucidating the reasons for the formation of a continuous or discontinuous series of mixed crystals as well as to explaining the distribution of the alkali (M + ) and halide (X − ) ions in the mixed-crystalline and liquid phases. The isodimorphism of potassium and rubidium chlorocarnallites (14,15) and potassium and ammonium chlorocarnallites (16) is the reason for the formation of a discontinuous series of mixed crystals.…”

Isodimorphic co-crystallization of isostructural ammonium chloro- and bromo-carnallites

“…(10) Due to its different composition, lithium chlorocarnallite, Li(H 2 O)Cl·MgCl 2 ·6H 2 O, crystallizes in space group C2/m. (8) Fluorocarnallites are not known.…”

“…(2)(3)(4)(5)(6)(7) Most double-salt chlorocarnallites, bromocarnallites, and iodocarnallites are isostructural and crystallize in a monoclinic crystal system (space group C2/c). (8,9) The only known exception is potassium chlorocarnallite which crystallizes in an orthorhombic crystal system. (10) Due to its different composition, lithium chlorocarnallite, Li(H 2 O)Cl·MgCl 2 ·6H 2 O, crystallizes in space group C2/m.…”