Manganese(II) chloride
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2008-05-30T14:29:08Z
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| ImageFile = Manganese(II)_chloride_tetrahydrate.jpg|
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| ImageName = Manganese(II) chloride tetrahydrate
| IUPACName = Manganese(II) chloride
| OtherNames = Manganous chloride
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| CASNo = 7773-01-5
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| Section2 = {{Chembox Properties
| Formula =
| MolarMass = anhydrous 125.844 g/mol; dihydrate 161.874 g/mol; tetrahydrate 197.91 g/mol
| Appearance =pink solid<br/>(''tetrahydrate'')
| Density = 3.0 g/cm³(solid)
| MeltingPt = 654 °C
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| BoilingPt = 1225 °C
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| Solubility = 72.3 g/100g
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| Section3 = {{Chembox Structure
| CrystalStruct = [[Cadmium chloride#Crystal structure|CdCl<sub>2</sub>]]
| Coordination = [[Octahedron|octahedral]]
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| Section8 = {{Chembox Related
| OtherAnions = [[Manganese(II) fluoride]]<br/>[[Manganese(II) bromide]]<br/>[[Manganese(II) iodide]]
| OtherCations = [[Manganese(III) chloride]]<br/>[[Technetium(IV) chloride]]<br/>[[Rhenium(IV) chloride]]
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| OtherCpds = [[Chromium(II) chloride]]<br/>[[Iron(II) chloride]]}}
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'''Manganese(II) chloride''' describes a series of compounds with the formula [[Manganese|Mn]][[chloride|Cl]]<sub>2</sub>(H<sub>2</sub>O)<sub>x</sub>, 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 [[water of crystallization|tetrahydrate]] MnCl<sub>2</sub>·4H<sub>2</sub>O, which consists of octahedral ''[[trans]]''-Mn(H<sub>2</sub>O)<sub>4</sub>Cl<sub>2</sub> molecules. The dihydrate MnCl<sub>2</sub>·2H<sub>2</sub>O is also known. Many Mn(II) species are characteristically pink, the paleness of the color being characteristic of transition metal complexes with [[high spin]] d<sup>5</sup> configurations.
==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 → MnCl<sub>2</sub> + H<sub>2</sub>
:MnCO<sub>3</sub> + 2 HCl → MnCl<sub>2</sub> + H<sub>2</sub>O + CO<sub>2</sub>
It also forms when [[manganese(IV) oxide]] is heated with concentrated hydrochloric acid; this reaction was once used for the manufacture of [[chlorine]].
:MnO<sub>2</sub> + 4 HCl → MnCl<sub>2</sub> + 2 H<sub>2</sub>O + Cl<sub>2</sub>
This reaction illustrates the oxidizing power of MnO<sub>2</sub> and the fact that oxides tend to exist in higher oxidation states than chlorides.
==Chemical properties==
MnCl<sub>2</sub> 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.,
:MnCl<sub>2</sub>([[aqueous|aq]]) + [[potassium carbonate|K<sub>2</sub>CO<sub>3</sub>]](aq) → [[manganese(II) carbonate|MnCO<sub>3</sub>]]([[solid|s]]) + 2 [[potassium chloride|KCl]]
In these equations, "MnCl<sub>2</sub>(aq)" refers to [Mn(H<sub>2</sub>O)<sub>6</sub>]<sup>2+</sup>, 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 [MnCl<sub>3</sub>]<sup><nowiki>−</nowiki></sup>, [MnCl<sub>4</sub>]<sup>2<nowiki>−</nowiki></sup> , and [MnCl<sub>6</sub>]<sup>4<nowiki>−</nowiki></sup>. Both [MnCl<sub>3</sub>]<sup><nowiki>−</nowiki></sup> and [MnCl<sub>4</sub>]<sup>2<nowiki>−</nowiki></sup> are [[polymer]]ic.
Upon treatment with typical organic ligands, manganese(II) undergoes oxidation by air to give Mn(III) [[Complex (chemistry)|complexes]]. Examples include [Mn([[EDTA]]]<sup><nowiki>−</nowiki></sup>, [Mn([[cyanide|CN]])<sub>6</sub>]<sup>3<nowiki>−</nowiki></sup>, and [Mn([[acetylacetonate]])]<sub>3</sub>. [[Triphenylphosphine]] forms a labile 2:1 [[adduct]]:
:MnCl<sub>2</sub> + 2 [[triphenylphosphine|Ph<sub>3</sub>P]] → [MnCl<sub>2</sub>(Ph<sub>3</sub>P)<sub>2</sub>]
Anhydrous manganese(II) chloride serves as a starting point for the synthesis of a variety of manganese compounds. For example, [[metallocene|manganocene]] is prepared by reaction of MnCl<sub>2</sub> with a solution of [[cyclopentadienyl complex|sodium cyclopentadienide]] in [[Tetrahydrofuran|THF]].
:MnCl<sub>2</sub> + 2 NaC<sub>5</sub>H<sub>5</sub> → Mn(C<sub>5</sub>H<sub>5</sub>)<sub>2</sub> + 2 NaCl
==Paramagnetism==
Manganese chloride is [[paramagnetic]], this fact is utilized when MnCl<sub>2</sub> is used as a contrast agent in [[MRI]] scanning. A dramatic example is using MnCl<sub>2</sub> to highlight neural pathways.
==Precautions==
[[Manganism]], or manganese poisoning, can be caused by long-term exposure to manganese dust or fumes.
==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.
==External links==
*[http://www.npi.gov.au/database/substance-info/profiles/52.html National Pollutant Inventory: Manganese and compounds Fact Sheet]
[[Category:Chlorides]]
[[Category:Manganese compounds]]
[[Category:Metal halides]]
[[de:Mangan(II)-chlorid]]
[[it:Cloruro manganoso]]
[[pl:Chlorek manganu(II)]]
[[fi:Mangaani(II)kloridi]]