Crystal Research and Technology
Cryst. Res. Technol. 39, 207 (2004) - Abstract -

Influence of complex formation upon inclusion of Mn(II), Co(II), Ni(II), and Cu(II) in ZnC2O4.2H2O

B. Donkova, J. Pencheva*, and M. Djarova

Faculty of Chemistry, University of Sofia, bul. James Bourchier 1, 1164 Sofia, Bulgaria
*University of Rousse, ul. Students 8, 7000 Rousse, Bulgaria

Keywords crystallization, coprecipitation, cocrystallization, impurity, inclusion, monooxalato complex, manganese(II), cobalt(II), nickel(II), copper(II), zinc(II) oxalate, sparingly soluble systems
PACS 61.66.Fn, 61.72.Q, 61.72.S, 64.70.D, 81.10.Dn
DOI 10.1002/crat.200310172

The inclusion of 3d-impurities Mn(II), Co(II), Ni(II) and Cu(II) in a crystalline precipitate of ZnC2O4.2H2O is investigated. This study is a part of the systematic one deal with the mechanism of inclusion of 3d-ions in sparingly soluble oxalate systems. The experiments are carried out in bi- end multi-component systems at two different mediums – one with deficiency of oxalate ions, another with excess. The insertion of 3d-ions upon mass crystallization of ZnC2O4.2H2O does not proceed by a simple ionic substitution. The results show that the inserted amount of impurity depends on some physicochemical characteristics of the neutral monooxalato complexes [MnC2O4]°, [CoC2O4]°, [NiC2O4]° and [CuC2O4]°. Good agreement between included impurity and the concentration of its complex in the solution is established. The stability constant of monooxalato complex affects the impurity inclusion. This effect depends on the medium nature. In the deficiency of oxalate ions the factor determining the inclusion is thermodynamic one – stability of monooxalato complexes. In the excess of oxalate ions inserted amount depends on kinetic factor – the formation rate of these complexes. In the term of that the insertion of Mn(II) is definitely different in the two mediums while that of the Ni (II) does not depend on the medium. The copper shows deviation from overall dependence in the two mediums due to the Jahn-Teller distortion. Its double decreasing insertion in the excess of oxalate ions is related with stabilization of [Cu(C2O4)2]2-. The conclusions presume that by varying the background medium and taking in view the ions present in the solution, the amount of inserted impurities can be predicted and controlled.



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