Manganese(II) chloride

Manganese chloride is produced by treating manganese(IV) oxide with concentrated hydrochloric acid.

:MnO₂ + 4 HCl → MnCl₂ + 2 H₂O + Cl₂

In the 19th century this reaction was used for the manufacture of chlorine. By carefully neutralizing the resulting solution with MnCO₃, one can selectively precipitate iron salts, which are common impurities in manganese dioxide.{{citation | first = Arno H. | last = Reidies | contribution = Manganese Compounds | title = Ullmann's Encyclopedia of Industrial Chemistry | publisher = Wiley-VCH | location = Weinheim | year = 2002 | doi = 10.1002/14356007.a16_123 | isbn = 978-3-527-30385-4}}.

In the laboratory, manganese chloride can be prepared by treating manganese metal or manganese(II) carbonate with hydrochloric acid:

:Mn + 2 HCl + 4 H₂O → MnCl₂(H₂O)₄ + H₂

:MnCO₃ + 2 HCl + 3 H₂O → MnCl₂(H₂O)₄ + CO₂

Anhydrous MnCl₂ adopts a layered cadmium chloride-like structure. The tetrahydrate consists of octahedral cis-Mn(H₂O)₄Cl₂ molecules. The trans isomer, which is metastable, is also known.{{cite journal|title=Crystal structure of manganese dichloride tetrahydrate|author1=Zalkin, Allan|author2=Forrester, J. D.|author3=Templeton, David H.|journal=Inorganic Chemistry|year=1964|volume=3|issue=4|pages=529–33|doi=10.1021/ic50014a017|url=http://www.escholarship.org/uc/item/7vf7p79j}}A. F. Wells, Structural Inorganic Chemistry, 5th ed., Oxford University Press, Oxford, UK, 1984. The dihydrate MnCl₂(H₂O)₂ is a coordination polymer. Each Mn center is coordinated to four doubly bridging chloride ligands. The octahedron is completed by a pair of mutually trans aquo ligands.{{cite journal|title=Crystal structures of manganese(II) and iron(II) chloride dihydrate|author1=Morosin, B.|author2=Graeber, E. J.|journal=Journal of Chemical Physics|year=1965|volume=42|issue=3|pages=898–901|doi=10.1063/1.1696078|bibcode=1965JChPh..42..898M}}

{{multiple image

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| footer = Structures of the forms of manganese(II) chloride

| image1 = manganese(II)-chloride-xtal-layer-top-infinite-3D-bs-17.png

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| caption1 = Anhydrous

| image2 = MX2(H2O)2.png

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| caption2 = Dihydrate}}

The hydrates dissolve in water to give mildly acidic solutions with a pH of around 4. These solutions consist of the metal aquo complex [Mn(H₂O)₆]²⁺.

It is a weak Lewis acid, reacting with chloride ions to produce a series of salts containing the following ions [MnCl₃]⁻, [MnCl₄]²⁻, and [MnCl₆]⁴⁻.

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 organomanganese compounds. For example, manganocene is prepared by reaction of MnCl₂ with a solution of sodium cyclopentadienide in tetrahydrofuran (THF).

:MnCl₂ + 2 NaC₅H₅ → Mn(C₅H₅)₂ + 2 NaCl

Similar reactions are used in the preparation of the antiknock compound methylcyclopentadienyl manganese tricarbonyl.

Manganese chloride is a precursor to organomanganese reagents in organic chemistry.{{cite journal |doi=10.15227/orgsyn.076.0239|title=Regioselective Monoalkylation of Ketones Via Their Manganese Enolates: 2-Benzyl-6-Methylcyclohexanone from 2-Methylcyclohexanone |journal=Organic Syntheses |year=1999 |volume=76 |page=239|author=Gérard Cahiez, François Chau, Bernard Blanchot }}{{cite journal |doi=10.15227/orgsyn.072.0135|title=Manganese-Copper-Catalyzed Conjugate Addition of Organomagnesium Reagents to a,b-Ethylenic Ketones\: 2-(1,1-Dimethylpentyl)-5-methyl-cyclohexanone from Pulegone |journal=Organic Syntheses |year=1995 |volume=72 |page=135|author=S. Marquais, M. Alami, and G. Cahiez }}

Manganese chloride is mainly used in the production of dry cell batteries.

Manganese(II) salts are paramagnetic. As such the presence of such salts profoundly affect NMR spectra.

{{Citation

| last1 = Frohlich

| first1 = Margret

| last2 = Brecht

| first2 = Volker

| last3 = Peschka-Suss

| first3 = Regine

| title = Parameters influencing the determination of liposome lamellarity by ^31P-NMR

| journal = Chemistry and Physics of Lipids

| volume = 109

| issue = 1

| pages = 103–112

| date = January 2001

| doi = 10.1016/S0009-3084(00)00220-6

| pmid = 11163348

}}

Scacchite is the natural, anhydrous form of manganese(II) chloride.{{Cite web|url=https://www.mindat.org/min-3549.html|title=Scacchite}}

Manganism, or manganese poisoning, can be caused by long-term exposure to manganese dust or fumes.

{{reflist}}

{{Commons category|Manganese(II) chloride}}

• [http://www.npi.gov.au/resource/manganese-compounds National Pollutant Inventory: Manganese and compounds Fact Sheet]

{{Manganese compounds}}

{{Chlorides}}

Category:Chlorides

Category:Manganese(II) compounds

Category:Metal halides