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]
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 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:
^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)
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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, PMID11163348