Strontium bromide is a chemical compound with a formula SrBr2. At room temperature it is a white, odourless, crystalline powder. Strontium bromide imparts a bright red colour in a flame test, showing the presence of strontium ions. It is used in flares and also has some pharmaceutical uses.
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| Names | |
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| IUPAC name
Strontium bromide
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| Identifiers | |
3D model (JSmol)
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| ChemSpider | |
| ECHA InfoCard | 100.030.868 |
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PubChem CID
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| UNII | |
CompTox Dashboard (EPA)
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| Properties | |
| SrBr2 | |
| Molar mass | 247.428 g/mol (anhydrous) 355.53 g/mol (hexahydrate) |
| Appearance | white crystalline powder |
| Density | 4.216 g/cm3 (anhydrous) 2.386 g/cm3 (hexahydrate) |
| Melting point | 643 °C (1,189 °F; 916 K) |
| Boiling point | 2,146 °C (3,895 °F; 2,419 K) |
| 107 g/100 mL | |
| Solubility | Soluble in ethanol Insoluble in diethyl ether |
| −86.6·10−6 cm3/mol | |
| Structure[1] | |
| Tetragonal | |
| P4/n (No. 85) | |
a = 1160.42 pm, c = 713.06 pm
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Formula units (Z)
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10 |
| Hazards | |
| Occupational safety and health (OHS/OSH): | |
Main hazards
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Corrosive |
| NFPA 704 (fire diamond) | |
| Related compounds | |
Other anions
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Other cations
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Preparation
editSrBr2 can be prepared from strontium hydroxide and hydrobromic acid.
- Sr(OH)2 + 2 HBr → SrBr2 + 2 H2O
Alternatively strontium carbonate can also be used as strontium source.
- SrCO3 + 2 HBr → SrBr2 + H2O + CO2(g)
These reactions give hexahydrate of strontium bromide (SrBr2·6H2O), which decomposes to dihydrate (SrBr2·2H2O) at 89 °C. At 180 °C anhydrous SrBr2 is obtained.[2]
Structure
editAt room temperature, strontium bromide adopts a crystal structure with a tetragonal unit cell and space group P4/n. This structure is referred to as α-SrBr2 and is isostructural with EuBr2 and USe2. The compound's structure was initially erroneously interpreted as being of the PbCl2 type,[3] but this was later corrected.[4][1]
Around 920 K (650 °C), α-SrBr2 undergoes a first-order solid-solid phase transition to a much less ordered phase, β-SrBr2, which adopts the cubic fluorite structure. The beta phase of strontium bromide has a much higher ionic conductivity of about 1 S/cm, comparable to that of molten SrBr2, due to extensive disorder in the bromide sublattice.[1] Strontium bromide melts at 930 K (657 °C).
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Distorted square antiprismatic coordination geometry of crystallographically independent strontium atom number 1 -
Square antiprismatic coordination geometry of strontium number 2 -
Flattened tetrahedral coordination geometry of bromine number 1 -
Distorted tetrahedral coordination geometry of bromine number 2 -
Tetrahedral coordination geometry of bromine number 3 -
Tetrahedral coordination geometry of bromine number 4
See also
editReferences
edit- ^ a b c Hull, Stephen; Norberg, Stefan T.; Ahmed, Istaq; Eriksson, Sten G.; Mohn, Chris E. (2011). "High temperature crystal structures and superionic properties of SrCl2, SrBr2, BaCl2 and BaBr2". J. Solid State Chem. 184 (11): 2925–2935. Bibcode:2011JSSCh.184.2925H. doi:10.1016/j.jssc.2011.09.004.
- ^ Dale L. Perry, Sidney L. Phillips: Handbook of Inorganic Compounds. CRC Press, 1995, ISBN 978-0-8493-8671-8, (Strontium bromide, p. 387, at Google Books).
- ^ Kamermans, M. A. (1939-12-01). "The Crystal Structure of SrBr2". Zeitschrift für Kristallographie - Crystalline Materials. 101 (1–6). Walter de Gruyter GmbH: 406–411. doi:10.1524/zkri.1939.101.1.406. ISSN 2196-7105. S2CID 102183214.
- ^ R. L. Sass; et al. (1963). "The crystal structure of strontium bromide". J. Phys. Chem. 67 (12): 2862. doi:10.1021/j100806a516.