Magnesium bromide

Magnesium bromide are inorganic compounds with the chemical formula MgBr₂(H₂O)_x, where x can range from 0 to 9. They are all white deliquescent solids. Some magnesium bromides have been found naturally as rare minerals such as: bischofite and carnallite.^[2][3]

Magnesium bromide^[1]

Identifiers
CAS Number	7789-48-2 (anhydrous) Y 13446-53-2 (hexahydrate) N 75198-45-7 (decahydrate) N
3D model (JSmol)	Interactive image
ChemSpider	74219 Y
ECHA InfoCard	100.029.246
PubChem CID	522691
UNII	2VC6P60SLN Y
CompTox Dashboard (EPA)	DTXSID7064865
InChI InChI=1S/2BrH.Mg/h2*1H;/q;;+2/p-2 Y Key: OTCKOJUMXQWKQG-UHFFFAOYSA-L Y InChI=1/2BrH.Mg/h2*1H;/q;;+2/p-2 Key: OTCKOJUMXQWKQG-NUQVWONBAY
SMILES [Mg+2].[Br-].[Br-]
Properties
Chemical formula	MgBr2 (anhydrous) MgBr2·6H2O (hexahydrate)
Molar mass	184.113 g/mol (anhydrous) 292.204 g/mol (hexahydrate)
Appearance	white hygroscopic hexagonal crystals (anhydrous) colorless monoclinic crystals (hexahydrate)
Density	3.72 g/cm3 (anhydrous) 2.07 g/cm3 (hexahydrate)
Melting point	711 °C (1,312 °F; 984 K) 172.4 °C, decomposes (hexahydrate)
Boiling point	1,250 °C (2,280 °F; 1,520 K)
Solubility in water	102 g/(100 mL) (anhydrous) 316 g/(100 mL) (0 °C, hexahydrate)
Solubility	ethanol: 6.9 g/(100 mL) methanol: 21.8 g/(100 mL)
Magnetic susceptibility (χ)	−72.0·10−6 cm3/mol
Structure
Crystal structure	Rhombohedral, hP3
Space group	P-3m1, No. 164
Coordination geometry	octahedral
Thermochemistry
Heat capacity (C)	70 J/(mol·K)
Std molar entropy (S⦵298)	117.2 J/(mol·K)
Std enthalpy of formation (ΔfH⦵298)	−524.3 kJ/mol
Hazards
NFPA 704 (fire diamond)	1 0 0
Safety data sheet (SDS)	External SDS
Related compounds
Other anions	Magnesium fluoride Magnesium chloride Magnesium iodide
Other cations	Beryllium bromide Calcium bromide Strontium bromide Barium bromide Radium bromide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

Synthesis

Magnesium bromide can be synthesized by treating magnesium oxide (and related basic salts) with hydrobromic acid.^[3] It can also be made by reacting magnesium carbonate and hydrobromic acids, and collecting the solid left after evaporation.^[2]

As suggested by its easy conversion to various hydrates, anhydrous MgBr₂ is a Lewis acid. In the coordination polymer with the formula MgBr₂(dioxane)₂, Mg²⁺ adopts an octahedral geometry.^[4]

Uses and reactions

Magnesium bromide is used as a Lewis acid catalyst in some organic synthesis, e.g., in aldol reaction.^[5]

Magnesium bromide also has been used as a tranquilizer^[2] and as an anticonvulsant for treatment of nervous disorders.^[6]

Magnesium bromide modifies the catalytic properties of palladium on charcoal.^[7]

Magnesium bromide hexahydrate has properties as a flame retardant.^[8]

Treatment of magnesium bromide with chlorine gives magnesium chloride. This reaction is employed in the production of magnesium chloride from brines.^[9]

Structure

Two hydrates are known, the hexahydrate and the nonahydrate. Several reports claim a decahydrate, but X-ray crystallography confirmed that it is a nonahydrate. The hydrates feature [Mg(H₂O)₆]²⁺ ions.^[10]

References

1. Lide, David R. (1998). Handbook of Chemistry and Physics (87 ed.). Boca Raton, Florida: CRC Press. pp. 4–67. ISBN 0-8493-0594-2.
2. Gruyter, W. Concise Encyclopedia Chemistry, Walter de Gruyter & Company: Berlin, 1993; 612
3. Lewis, R.J. Hawley’s Condensed Chemical Dictionary, 15th ed.; John Wiley & Sons Inc.:New York, 2007; 777
4. Fischer, Reinald; Görls, Helmar; Meisinger, Philippe R.; Suxdorf, Regina; Westerhausen, Matthias (2019). "Structure–Solubility Relationship of 1,4-Dioxane Complexes of Di(hydrocarbyl)magnesium". Chemistry – A European Journal. 25 (55): 12830–12841. doi:10.1002/chem.201903120. PMC 7027550. PMID 31328293.
5. Evans, David A.; Tedrow, Jason S.; Shaw, Jared T.; Downey, C. Wade (2002). "Diastereoselective Magnesium Halide-Catalyzed anti-Aldol Reactions of Chiral N-Acyloxazolidinones". Journal of the American Chemical Society. 124 (3): 392–393. doi:10.1021/ja0119548. PMID 11792206.
6. Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0-07-049439-8
7. Bouzide, Abderrahim (2002). "Magnesium Bromide Mediated Highly Diastereoselective Heterogeneous Hydrogenation of Olefins". Organic Letters. 4 (8): 1347–50. doi:10.1021/ol020032m. PMID 11950359.
8. Mostashari, S. M.; Fayyaz, F. (2008). "XRD characterization of the ashes from a burned cellulosic fabric impregnated with magnesium bromide hexahydrate as flame-retardant". Journal of Thermal Analysis and Calorimetry. 92 (3): 845. doi:10.1007/s10973-007-8928-4. S2CID 94416902.
9. Seeger, Margarete; Otto, Walter; Flick, Wilhelm; Bickelhaupt, Friedrich; Akkerman, Otto S. (2000). "Magnesium Compounds". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a15_595. ISBN 3-527-30673-0.
10. Hennings, Erik; Schmidt, Horst; Voigt, Wolfgang (2013). "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". Acta Crystallographica Section C Crystal Structure Communications. 69 (11): 1292–1300. doi:10.1107/S0108270113028138. PMID 24192174.