Manganese(II) chloride
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| Manganese(II) chloride | |
|---|---|
_chloride_tetrahydrate.jpg/200px-Manganese(II)_chloride_tetrahydrate.jpg) |
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| IUPAC name | Manganese(II) chloride |
| Other names | Manganous chloride |
| Identifiers | |
| CAS number | [7773-01-5] |
| Properties | |
| Molar mass | anhydrous 125.844 g/mol; dihydrate 161.874 g/mol; tetrahydrate 197.91 g/mol |
| Appearance | pink solid (tetrahydrate) |
| Density | 3.0 g/cm³(solid) |
| Melting point |
654 °C |
| Boiling point |
1225 °C |
| Solubility in water | 72.3 g/100g |
| Structure | |
| Crystal structure | CdCl2 |
| Coordination geometry |
octahedral |
| Related compounds | |
| Other anions | Manganese(II) fluoride Manganese(II) bromide Manganese(II) iodide |
| Other cations | Manganese(III) chloride Technetium(IV) chloride Rhenium(IV) chloride |
| Related compounds | Chromium(II) chloride Iron(II) chloride |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references |
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Manganese(II) chloride describes a series of compounds with the formula MnCl2(H2O)x, where the value of x can be 0, 2, or 4. The tetrahydrate is a pink salt that occurs naturally as the rare mineral scacchite. Most commonly, the term "manganese(II) chloride" refers to the tetrahydrate MnCl2·4H2O, which consists of octahedral trans-Mn(H2O)4Cl2 molecules. The dihydrate MnCl2·2H2O is also known. Many Mn(II) species are characteristically pink, the paleness of the color being characteristic of transition metal complexes with high spin d5 configurations.
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[edit] Preparation
Manganese(II) chloride can be prepared by treating manganese metal or manganese(II) carbonate with hydrogen chloride or hydrochloric acid, depending on whether one seeks the anhydrous or hydrated forms:
- Mn + 2 HCl → MnCl2 + H2
- MnCO3 + 2 HCl → MnCl2 + H2O + CO2
It also forms when manganese(IV) oxide is heated with concentrated hydrochloric acid; this reaction was once used for the manufacture of chlorine.
- MnO2 + 4 HCl → MnCl2 + 2 H2O + Cl2
This reaction illustrates the oxidizing power of MnO2 and the fact that oxides tend to exist in higher oxidation states than chlorides.
[edit] Chemical properties
MnCl2 is a polymeric solid which adopts a layered structure. The hydrates dissolve in water to give mildly acidic solutions with a pH of around 4. Such aqueous solutions are used to prepare a variety of manganese compounds, e.g.,
In these equations, "MnCl2(aq)" refers to [Mn(H2O)6]2+, which is the principal form of manganese in aqueous solutions of any manganese chloride.
It is a weak Lewis acid, reacting with chloride ions to produce a series of solids containing the following ions [MnCl3]−, [MnCl4]2− , and [MnCl6]4−. Both [MnCl3]− and [MnCl4]2− are polymeric.
Upon treatment with typical organic ligands, manganese(II) undergoes oxidation by air to give Mn(III) complexes. Examples include [Mn(EDTA]−, [Mn(CN)6]3−, and [Mn(acetylacetonate)]3. Triphenylphosphine forms a labile 2:1 adduct:
- MnCl2 + 2 Ph3P → [MnCl2(Ph3P)2]
Anhydrous manganese(II) chloride serves as a starting point for the synthesis of a variety of manganese compounds. For example, manganocene is prepared by reaction of MnCl2 with a solution of sodium cyclopentadienide in THF.
- MnCl2 + 2 NaC5H5 → Mn(C5H5)2 + 2 NaCl
[edit] Paramagnetism
Manganese chloride is paramagnetic, this fact is utilized when MnCl2 is used as a contrast agent in MRI scanning. A dramatic example is using MnCl2 to highlight neural pathways.
[edit] Precautions
Manganism, or manganese poisoning, can be caused by long-term exposure to manganese dust or fumes.
[edit] References
- N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, 2nd ed., Butterworth-Heinemann, Oxford, UK, 1997.
- Handbook of Chemistry and Physics, 71st edition, CRC Press, Ann Arbor, Michigan, 1990.
- A. F. Wells, 'Structural Inorganic Chemistry, 5th ed., Oxford University Press, Oxford, UK, 1984.
- The Merck Index, 7th edition, Merck & Co, Rahway, New Jersey, USA, 1960.
- Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
