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Published: Kem. Ind. 52 (7-8) (2003) 313–318
Paper reference number: KUI-41/2002
Paper type: Conference paper
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Polarographic Study of Hg(II)- Crown ethers Complexes in Nonaqeous Solvents

A. Cipurković, R. Kubiček, J. Budimir and S. Marić


The chemistry of crown compounds forms an important part of literature today. These studies mainly deal with the stability and selectivity of metal complexes of crown compounds and with their applications, such as their role as an ionophore in the construction of ion selective electrodes, in ion exchange membrane, in the preparation and preconcentration of metal cations, as a stationary phase in chromatography and in the design of fiber optic chemical sensors. Compared to enormous research work devoted to the study of alkali and alkaline earth complexes of crown compounds, little has been focused on the complexation of Hg(II). It is well known that the selectivity of complexation strongly depends on the solvating ability of the solvent with respect to the cation and ligand. As a result, variations in the nature of the solvent produce significant changes in the binding properties of the macrocyclic ligand, so that the stability and selectivity of the complexes can be greatly altered. Among the various physicochemical methods, which have been used for the research of these complexes, the polarographic techniques are very useful means for determining the electrochemical behaviour of these macrocyclic compounds. In polarographic investigation, the significant quantity for studying the stability of the metal ion complexes was the half-wave potential (E1/2) of the differential pulse peak potential (Ep) of the complex and the free metal ion. The difference in E1/2 between the complex and metal ion was used in calculation of the stability constants of the complex. The goal of the present work is the investigation of the effects of the solvent properties on the stability of macrocyclic complexes Hg(II) with 18-crown-6 (18C6) and hexathia-18-crown-6 (18S6). We report here the results obtained from the polarographic investigation of complexation reaction in acetonitrile and nitrobenzene at temperatures 25 ± 0.5 °C. The stability of the resulting 1:1 complexes vary in the order 18S6 > 18C6, for both solvents, nitrobenzene and acetonitrile. The stability for 18S6 in acetonitrile and nitrobenzene solutions are about ten to twelve orders of magnitude larger than 18C6. There is an inverse relationship between the complexes stability and the Gutmann donor number of solvents.

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mercury, crown ethers, complexation, DP polarography