Manganese(II) chloride


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

Preparation

Manganese chloride is produced by treating manganese oxide with concentrated hydrochloric acid.
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.
In the laboratory, manganese chloride can be prepared by treating manganese metal or manganese carbonate with hydrochloric acid:

Structures

Anhydrous MnCl2 adopts a layered cadmium chloride-like structure. The tetrahydrate consists of octahedral cis-Mn4Cl2 molecules. The trans isomer, which is metastable, is also known. The dihydrate MnCl22 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.

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 2+.
It is a weak Lewis acid, reacting with chloride ions to produce a series of solids containing the following ions −, 2−, and 4−. Both − and 2− are polymeric.
Upon treatment with typical organic ligands, manganese undergoes oxidation by air to give Mn complexes. Examples include −, 3−, and . Triphenylphosphine forms a labile 2:1 adduct:
Anhydrous manganese 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.

NMR

Aqueous solutions of manganese chloride are used in 31P-NMR to determine the size and lamellarity of phospholipid vesicles. 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.

Natural occurrence

Scacchite is the natural, anhydrous form of manganese chloride. The only other currently known mineral systematized as manganese chloride is kempite - a representative of the atacamite group, a group of hydroxide-chlorides.

Applications

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

Precautions

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