Manganese(II) chloride

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]

Manganese(II) chloride

molecular structure
Tetrahydrate
Names
IUPAC names Manganese(II) chloride Manganese dichloride
Other names Manganous chloride hyperchloride of manganese
Identifiers
CAS Number	7773-01-5^Y 38639-72-4 (dihydrate)^Y 13446-34-9 (tetrahydrate) ^Y
3D model (JSmol)	Interactive image
ChEMBL	ChEMBL1200693^N
ChemSpider	22888^Y
ECHA InfoCard	100.028.972
PubChem CID	24480
RTECS number	OO9625000
UNII	6YB4901Y90^Y
CompTox Dashboard (EPA)	DTXSID9040681
InChI InChI=1S/2ClH.Mn/h2*1H;/q;;+2/p-2^Y Key: GLFNIEUTAYBVOC-UHFFFAOYSA-L^Y InChI=1S/2ClH.Mn/h2*1H;/q;;+2/p-2 Key: GLFNIEUTAYBVOC-NUQVWONBAP Key: GLFNIEUTAYBVOC-UHFFFAOYSA-L
SMILES Cl[Mn]Cl
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/cm^3 (anhydrous) 2.27 g/cm^3 (dihydrate) 2.01 g/cm^3 (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 cm^3/mol
Structure
Crystal structure	CdCl2
Coordination geometry	octahedral
Hazards
NFPA 704 (fire diamond)	0 2 0
Flash point	Non-flammable
Lethal dose or concentration (LD, LC):
LD50 (median dose)	250-275 mg/kg (rat, oral) 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

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]

Sample of anhydrous MnCl₂.

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]

Subunit of MnCl₂(H₂O)₂ lattice.

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 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

NMR

Aqueous solutions of manganese(II) chloride are used in ³¹P-NMR to determine the size and lamellarity of phospholipid vesicles.[7] When manganese chloride is added to a vesicular solution, Mn²⁺ paramagnetic ions are released, perturbing the relaxation time of the phospholipids' phosphate groups and broadening the resulting ³¹P resonance signal. Only phospholipids located in the outermost monolayer exposed to Mn²⁺ experience this broadening. The effect is negligible for multilamellar vesicles, but for large unilamellar vesicles, a ~50% reduction in signal intensity is observed.[8]

Natural occurrence

Scacchite is the natural, anhydrous form of manganese(II) chloride.[9] The only other currently known mineral systematized as manganese chloride is kempite - a representative of the atacamite group, a group of hydroxide-chlorides.[10]

Applications

Manganese chloride is mainly used in the production of dry cell batteries. It is the precursor to the antiknock compound methylcyclopentadienyl manganese tricarbonyl.[3]

Precautions

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

References

1. "Manganese compounds (as Mn)". Immediately Dangerous to Life and Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
2. N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, 2nd ed., Butterworth-Heinemann, Oxford, UK, 1997.
3. 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.
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.
5. A. F. Wells, Structural Inorganic Chemistry, 5th ed., Oxford University Press, Oxford, UK, 1984.
6. 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.
7. 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
8. Hope M, Bally M, Webb G, Cullis P (April 10, 1984), "Production of large unilamellar vesicles by a rapid extrusion procedure. Characterization of size distribution, trapped volume and ability to maintain a membrane potential" (PDF), Biochimica et Biophysica Acta (BBA) - Biomembranes, 812 (1): 55–65, doi:10.1016/0005-2736(85)90521-8, PMID 23008845
9. https://www.mindat.org/min-3549.html
10. https://www.mindat.org/min-2183.html

External links

• National Pollutant Inventory: Manganese and compounds Fact Sheet