Studies of Mixed Valence Manganese Compounds

5 STUDIES OF MIXED VALENCE MANGANESE COMPOUNDS Mn304 is a commercial product which has a normal spinal structure with one Mn(ll) and two Mn(III) ions per formula. However, some complexes contain one Mn(III) and one Mn(IV) per formula and they are also considered mixed valence complexes. Most of the reactions of these compounds are oxidations in which Mn is reduced to the most stable state of +2. 

2 Preparations, Tests and Analysis of MnOfphenlxL (C104)3.2H20 

This complex is obtained by the oxidation of Mn(III) by permanganate in presence of the ligand. It can be analysed by dissolving in a known excess of fireshly prepared standard ascorbic acid solution and back titrating the excess with Mn(IIl) sulphate solution. 

1 g of KMn04 in 50 cm water, added dropwise keeping the temperature between 0 C and -5 C. Allow the mixture to stand in the ice bath for 15 minutes. Filter under suction and add to the filtrate 40% w/w of NaC104 dropwise to precipitate the required complex. Collect the solid by filtration under suction, wash with 15 cm of 50/50 ethanol/ether mixture and dry by continued suction while pressing between filter paper. Record the mass of the product and calculate the percentage yield based on phenanthroline (phen). 

Weigh out accurately about 0.2S g of your preparation into a conical flask. Cover with water and add from a burette freshly prepared and standardised 0.05 M ascorbic acid. Shake well until the solid dissolves and then add 10.0 cm acid in excess. Back titrate the excess ascorbic acid against freshly prepared and standardised Mn(IlI) solution using ferroin as indicator. Repeat and calculate from the average results the percentage Mn in your preparation and hence its percentage purity. 

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