Silver Cation Coordination Study to AsW9 Ligand – A Trilacunar Arsenotungstate Compound

DOI: 10.1515/amma-2017-0018

Objective: The main objective of this research is to find the coordination ratio between AsW9 and Ag+, as a preliminary study for synthesizing a new silver-arsenotungstate complex.
Material and method: The ligand:cation molar ratio in complexes was determined by conductometric and potentiometric titrations of AsW9 with silver salts: CH3COOAg, AgNO3.
Results: The ratio was obtained from the inflexion points of the curves when molar ratio was plotted versus conductivity, or from the equivalence point when silver added volume was plotted versus pH value. Each graphic shows one point of inflexion corres ponding to 1:1.54 ratio of AsW9:Ag+. In the same manner, the equivalent volumes determined by graphical method gave the ratio 1:1.53. The spectral results confirmed that a AsW9:Ag+ complex was formed since the ligand absorption maxima values have been changed from 190 nm to 197 nm in the case of using AgNO3 and 196 nm for CH3COOAg corresponding to the W=Od bond, and from 246,5 nm to 274 nm (AgNO3) and 270 nm (CH3COO-Ag+) for the W-Ob,c-W bond.
Conclusions: Silver cation exhibit a preference for AsW9 in a ratio of 3 to 2. This ratio can be associated to a sandwich type arrangement, with two trilacunary Keggin building blocks incorporating 3 metal cations in a tetrahedral geometry.

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