Manganese(II) chloride

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Manganese(II) chloride
Cis-MnCl2(H2O)4.png
molecular structure
Manganese(II) chloride tetrahydrate.jpg
Tetrahydrate
Names
IUPAC names
Manganese(II) chloride
Manganese dichloride
Other names
Manganous chloride
hyperchloride of managnese
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.028.972
RTECS number OO9625000
UNII
Properties
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)
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
+14,350·10−6 cm3/mol
Structure
CdCl2
octahedral
Hazards
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
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).
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Infobox references

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 the most common form of "manganese(II) chloride" and is the tetrahydrate with the formula MnCl2·4H2O. The anhydrous form and a dihydrate MnCl2·2H2O are also known. 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[edit]

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 and hydrochloric acid:

Mn + 2 HCl + 4 H2O → MnCl2(H2O)4 + H2
MnCO3 + 2 HCl + 3 H2O → MnCl2(H2O)4 + CO2

Structures[edit]

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[edit]

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[edit]

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 negligle for multilamellar vesicles, but for large unilamellar vesicles, a ~50% reduction in signal intensity is observed.[8]

Applications[edit]

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[edit]

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

References[edit]

  1. ^ "Manganese compounds (as Mn)". Immediately Dangerous to Life and Health. 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. ^ a b Reidies, Arno H. (2002), "Manganese Compounds", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, ISBN 3-527-30385-5, doi:10.1002/14356007.a16_123 .
  4. ^ Zalkin, Allan; Forrester, J. D.; Templeton, David H. (1964). "Crystal structure of manganese dichloride tetrahydrate". Inorganic Chemistry. 3: 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: 898–901. 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, PMID 11163348, doi:10.1016/S0009-3084(00)00220-6 
  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, 812: 55–65, doi:10.1016/0005-2736(85)90521-8 

External links[edit]