The nature of Mn(II) complexes in concentrated aqueous ammonium oxalate solutions

The paper presents an analysis of the results of spectroscopic studies obtained in the ultraviolet range UV for unsaturated ammonium oxalate solutions containing Mn(II) impurity c i . The aim is to follow manganese oxalate formation processes at different ammonium oxalate concentrations c and Mn(II) impurity c i and also to establish how concentrations of particular species change with a change of ratio ( c i / c ). Spectroscopic analysis is discussed from the standpoint of speciation of these complexes in the abovementioned solutions. The coordination of C 2 O 4 2– ligand with Mn(H 2 O) 6 2+ aquacomplex in the range ‐2 < ln( c i / c ) < 1.5 leads to the formation of Mn(C 2 O 4 ) and Mn(C 2 O 4 ) 2 2– complexes, but the coordination of the C 2 O 4 2– ligand with Mn(C 2 O 4 ) 2 2– complex in the concentration ratio range ‐5 < ln( c i / c ) < ‐2 results in the formation of predominantly Mn(C 2 O 4 ) 3 4– complex. The effect of successive coordination of the C 2 O 4 2– ligand is well‐defined in the ultraviolet spectral region. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)