Manganese(II) chloride

Manganese(II) chloride
Names
ball-and-stick model of crystal packing
molecular structure
Tetrahydrate
IUPAC names Manganese(II) chloride Manganese dichloride
Other names Manganous chloride hyperchloride of manganese
Identifiers
CAS Number	7773-01-5^Y 20603-88-7 (dihydrate)^N 13446-34-9 (tetrahydrate)^Y
3D model (JSmol)	anhydrous: Interactive image tetrahydrate: Interactive image
ChEMBL	ChEMBL1200693^N
ChemSpider	22888^Y
ECHA InfoCard	100.028.972
PubChem CID	24480
RTECS number	OO9625000
UNII	6YB4901Y90^Y QQE170PANO (tetrahydrate)^Y
CompTox Dashboard (EPA)	DTXSID9040681
InChI InChI=1S/2ClH.Mn/h21H;/q;;+2/p-2^Y Key: GLFNIEUTAYBVOC-UHFFFAOYSA-L^Y InChI=1S/2ClH.Mn/h21H;/q;;+2/p-2 Key: GLFNIEUTAYBVOC-NUQVWONBAP Key: GLFNIEUTAYBVOC-UHFFFAOYSA-L
SMILES anhydrous: [Mn+2].[Cl-].[Cl-] tetrahydrate: Cl[Mn-4]([OH2+])(Cl)([OH2+])([OH2+])[OH2+]
Properties
Chemical formula	MnCl₂
Molar mass	125.844 g/mol (anhydrous) 161.874 g/mol (dihydrate) 197.91 g/mol (tetrahydrate)
Appearance	pink solid (tetrahydrate)
Density	2.977 g/cm³ (anhydrous) 2.27 g/cm³ (dihydrate) 2.01 g/cm³ (tetrahydrate)
Melting point	654 °C (1,209 °F; 927 K) (anhydrous) dihydrate dehydrates at 135 °C tetrahydrate dehydrates at 58 °C
Boiling point	1,225 °C (2,237 °F; 1,498 K)
Solubility in water	63.4 g/100 ml (0 °C) 73.9 g/100 ml (20 °C) 88.5 g/100 ml (40 °C) 123.8 g/100 ml (100 °C)
Solubility	slightly soluble in pyridine, soluble in ethanol insoluble in ether
Magnetic susceptibility (χ)	+14,350·10⁻⁶ cm³/mol
Structure
Crystal structure	CdCl₂
Coordination geometry	octahedral
Hazards
NFPA 704 (fire diamond)	2 0 0
Flash point	Non-flammable
Lethal dose or concentration (LD, LC):
LD₅₀ (median dose)	250-275 mg/kg (rat, oral)^{[citation needed]} 1715 mg/kg (mouse, oral)^[1]
Related compounds
Other anions	Manganese(II) fluoride Manganese(II) bromide Manganese(II) iodide
Other cations	Manganese(III) chloride Technetium(IV) chloride Rhenium(III) chloride Rhenium(IV) chloride Rhenium(V) chloride Rhenium(VI) chloride
Related compounds	Chromium(II) chloride Iron(II) chloride
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

Chemical compound

Manganese(II) chloride is the dichloride salt of manganese, MnCl₂. This inorganic chemical exists in the anhydrous form, as well as the dihydrate (MnCl₂·2H₂O) and tetrahydrate (MnCl₂·4H₂O), with the tetrahydrate being the most common form. Like many Mn(II) species, these salts are pink, with the paleness of the color being characteristic of transition metal complexes with high spin d⁵ configurations.^[2]

Preparation

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

MnO₂ + 4 HCl → MnCl₂ + 2 H₂O + Cl₂

This reaction was once 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.^[3]

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

Structures

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.^[4]^[5] 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.^[6]

Chemical properties

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.^[3]

Manganese chloride is a precursor to organomanganese reagents in organic chemistry.^[7]^[8]

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

Magnetism

Manganese(II) salts are paramagnetic. As such the presence of such salts profoundly affect NMR spectra.^[9]

Natural occurrence

Scacchite is the natural, anhydrous form of manganese(II) chloride.^[10]

Precautions

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

References

^ "Manganese compounds (as Mn)". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
^ N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, 2nd ed., Butterworth-Heinemann, Oxford, UK, 1997.
^ ^a ^b Reidies, Arno H. (2002), "Manganese Compounds", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, doi:10.1002/14356007.a16_123, ISBN 978-3-527-30385-4.
^ Zalkin, Allan; Forrester, J. D.; Templeton, David H. (1964). "Crystal structure of manganese dichloride tetrahydrate". Inorganic Chemistry. 3 (4): 529–33. doi:10.1021/ic50014a017.
^ A. F. Wells, Structural Inorganic Chemistry, 5th ed., Oxford University Press, Oxford, UK, 1984.
^ Morosin, B.; Graeber, E. J. (1965). "Crystal structures of manganese(II) and iron(II) chloride dihydrate". Journal of Chemical Physics. 42 (3): 898–901. Bibcode:1965JChPh..42..898M. doi:10.1063/1.1696078.
^ Gérard Cahiez, François Chau, Bernard Blanchot (1999). "Regioselective Monoalkylation of Ketones Via Their Manganese Enolates: 2-Benzyl-6-Methylcyclohexanone from 2-Methylcyclohexanone". Organic Syntheses. 76: 239. doi:10.15227/orgsyn.076.0239.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^ S. Marquais, M. Alami, and G. Cahiez (1995). "Manganese-Copper-Catalyzed Conjugate Addition of Organomagnesium Reagents to a,b-Ethylenic Ketones\: 2-(1,1-Dimethylpentyl)-5-methyl-cyclohexanone from Pulegone". Organic Syntheses. 72: 135. doi:10.15227/orgsyn.072.0135.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^ Frohlich, Margret; Brecht, Volker; Peschka-Suss, Regine (January 2001), "Parameters influencing the determination of liposome lamellarity by ^31P-NMR", Chemistry and Physics of Lipids, 109 (1): 103–112, doi:10.1016/S0009-3084(00)00220-6, PMID 11163348
^ "Scacchite".