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Manganese(III) chloride
Chemical compound From Wikipedia, the free encyclopedia
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Manganese(III) chloride is the hypothetical inorganic compound with the formula MnCl3.
The existence of this binary halide has not been demonstrated.[1][2] Nonetheless, many derivatives of MnCl3 are known, such as MnCl3(THF)3 and the bench-stable MnCl3(OPPh3)2. Contrasting with the elusive nature of MnCl3, trichlorides of the adjacent metals on the periodic table—iron(III) chloride, chromium(III) chloride, and technetium(III) chloride—are all isolable compounds.
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History of MnCl3 and its adducts
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MnCl3 was claimed to be a dark solid and produced by the reaction of "anhydrous manganese(III) acetate" and liquid hydrogen chloride at −100 °C and decomposes above -40 °C.[3] Other claims involved reaction of manganese(III) oxide, manganese(III) oxide-hydroxide, and basic manganese acetate with hydrochloric acid. Given recent investigations however, such claims have been disproved or called into serious doubt.[4] Specifically, all known compounds containing MnCl3 are known to be solvent or ligand-stabilized adducts.
Adducts
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MnCl3 can be stabilized by complexation to diverse Lewis bases, as has been established over the course of many years of study.[4] Meta stable acetonitrile-solvated Mn(III)Cl3 can be prepared at room temperature by treating [Mn12O12(OAc)16(H2O)4] with trimethylsilyl chloride.[5] The treatment of permanganate salts with trimethylsilylchloride generates solutions containing Mn(III)–Cl species for alkene dichlorination reactions;[6][7][8] electrocatalytic methods that use Mn(III)–Cl intermediates have been developed for the same purpose.[9][10]
The reaction of manganese dioxide with hydrochloric acid in tetrahydrofuran gives MnCl3(H2O)(THF)2.[4] Manganese(III) fluoride suspended in THF reacts with boron trichloride, giving MnCl3(THF)3 which has the appearance of dark purple prisms.[4] This compound has a monoclinic crystal structure, reacts with water, and decomposes at room temperature.[4]
The most readily handled of this series of adducts is MnCl3(OPPh3)2.[11]
Pentachloromanganate(III)
Another common manganese(III) chloride compound is the pentachloromanganate(III) dianion. It is usually charge balanced with counterion(s) like tetraethylammonium.[12] The pentachloromanganates are typically green in color, light sensitive, maintain pentacoordination in solution, and have S = 2 ground states at room temperature.[12][13] Crystal structures of pentachloromanganate indicate the anion is square pyramidal.[14][15] Tetraethylammonium pentachloromanganate(III), [Et4N]2[MnCl5], can be prepared and isolated by treating suspension of [Mn12O12(OAc)16(H2O)4] in diethyl ether with trimethylsilylchloride, collecting the resulting purple solid in the dark, and then treating this solid with 0.6 M solution of tetraethylammonium chloride.[5] The green product is air stable but should be kept in the dark.
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Manganese(III) monochloride compounds
Some manganese compounds with macrocyclic tetradentate coordination can stabilize the manganese(III) monochloride, Mn(III)–Cl, moiety. Jacobson's catalyst is an example of a coordination compound containing the Mn(III)–Cl moiety and is stabilized by N,N,O,O coordination from a salen ligand. Jacobson's catalyst and related Mn(III)–Cl complexes react with O-atom transfer reagents to form high-valent Mn(V)O that are reactive in alkene epoxidation. Tetraphenylporphyrin Mn(III)Cl is a related commercially available compound.
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Other manganese(III) chloride complexes
References
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