Manganese solution chemistry

Syn-sedimentary chemical deposits form by chemical and biochemical precipitation of valuable metal components carried in solution, concomitant with the formation of the enclosing sedimentary rock. The manner of such deposition depends on the concentration of the metal in the solvent, the solubility of the precipitating product, the solution chemistry, and the deposition environment. Iron, manganese, phosphorus, lead, zinc, sulfur and uranium are some of the elements that have formed economically valuable deposits by chemical precipitation during sedimentation. 

Sadana U.S., Takkar P.N. Effect of sodality and zinc on soil solution chemistry of manganese under submergerged conditions. J Agr Sci 1988 111 51-55. 

Manganese represents the epitome of that characteristic property of the transition element namely the variable oxidation state. The aqueous solution chemistry includes all oxidation states from Mn(II) to Mn(VII), although these are of varying stability. Recently attention has been focused on polynuclear manganese complexes as models for the cluster of four manganese atoms which in conjunction with the donor side of Photosystem(II) is believed involved in plant photosynthetic oxidation of water. The Mn4 aggregate cycles between 6 distinct oxidation levels involving Mn(II) to Mn(IV). 

This volume of the Handbook illustrates the rich variety of topics covered by rare earth science. Three chapters are devoted to the description of solid state compounds skutteru-dites (Chapter 211), rare earth-antimony systems (Chapter 212), and rare earth-manganese perovskites (Chapter 214). Two other reviews deal with solid state properties one contribution includes information on existing thermodynamic data of lanthanide trihalides (Chapter 213) while the other one describes optical properties of rare earth compounds under pressure (Chapter 217). Finally, two chapters focus on solution chemistry. The state of the art in unraveling solution structure of lanthanide-containing coordination compounds by paramagnetic nuclear magnetic resonance is outlined in Chapter 215. The potential of time-resolved, laser-induced emission spectroscopy for the analysis of lanthanide and actinide solutions is presented and critically discussed in Chapter 216. 

In aqueous solution, the insoluble Mn02 is formed readily. Much of the manganese (IV) chemistry involves O-donor ligands. The compounds are generally high-spin d (S = 3/2) species and many are octahedral showing magnetic moments close to the spin-only value of 3.87 /ub. 

For an element exhibiting several different oxidation states in aqueous solution, we must consider a number of different half-reactions in order to obtain a clear picture of its solution chemistry. Consider manganese as an example aqueous solution species may contain manganese in oxidation states ranging from Mn(II) to Mn(VII), and equations 7.42-7.46 give half-reactions for which standard reduction potentials can be determined experimentally. 

An interesting new area of manganese(I) chemistry is opened up by the recent report of the first transition metal compound of the tetrahydroalane(III) anion [Mn(AlH4)(dmpe)2] (where dmpe = l,2-bis(dimethylphosphino)ethane. This yellow, diamagnetic compound was prepared from [MnBr2(dmpe)2] and excess UAIH4 in toluene. It appears to be monomeric in solution, with a bidentate AlH moiety, but an X-ray structure determination of the solid shows that two alane moieties bridge to form the dimer (2). 

The solution chemistry of manganese is relatively simple. The aquo-ion is resistant to oxidation in acidic or neutral solutions. It does not begin to hydrolyze until pH 10, and therefore free Mn " " can be present in neutral solutions at relatively high concentrations. Divalent manganese is a 3d ion and typically forms high-spin complexes lacking... 

Equations 17—20 result from contact between hot metal and slag, and the sulfur and carbon come dissolved in the hot metal. Likewise, the manganese, siUcon, and phosphoms which are produced are dissolved into the hot metal. The heats of solution for these elements in some cases depend on concentration, and are not included in the heats of reaction Hsted above. The ratio of the concentration of the oxide (or element for sulfur) in the slag to the concentration of the element in the hot metal is the partition ratio, and is primarily a function of slag chemistry and temperature. 

The chemistry of technetium(II) and rhenium(II) is meagre and mainly confined to arsine and phosphine complexes. The best known of these are [MCl2(diars)2], obtained by reduction with hypophosphite and Sn respectively from the corresponding Tc and Re complexes, and in which the low oxidation state is presumably stabilized by n donation to the ligands. This oxidation state, however, is really best typified by manganese for which it is the most thoroughly studied and, in aqueous solution, by far the most... 

Some aspects of the chemistry of manganese(III) in aqueous solution. G. Davies, Coord. Chem. Rev., 1969,4,199-224(101). 

Atkinson, G. Kor, S. K. (1965). The kinetics of ion association in manganese sulphate solutions. I. Results in water, dioxane-water mixtures, and methanol-water mixtures at 25 °C. Journal of Physical Chemistry, 69, 128-33. 

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