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    STUDIA CHEMIA - Issue no. 4(I) / 2009  
         
  Article:   SYNTHESIS, SPECTROSCOPIC AND ELECTROCHEMICAL CHARACTERIZATION OF A NEW CHROMIUM (III) SUBSTITUTED DAWSON POLYOXOMETALATE.

Authors:  ADRIAN-RAUL TOMŞA, ANA-MARIA TODEA, RADU SILAGHI-DUMITRESCU, GRIGORE DAMIAN, MARIANA RUSU. 		 
       
         
  Abstract:  A new chromium (III) substituted Dawson 2-molybdo-15-tungsto-2-phosphate K7[Cr(H2O)P2Mo2W15O61]•17H2O was synthesized by reaction of Cr(III) chloride with monolacunary Dawson molybdo-tungsto-diphosphates [P2Mo2W15O61]10- in aqueous solution. The complex has been characterized using spectroscopic and electrochemical techniques. The FT-IR spectroscopic data indicate that the polyanion overall symmetry is restored after the coordination of Cr(III). Coordination of chromium (III) is further supported by the 31P-NMR, EPR and UV-Vis electronic absorption spectroscopy results. Cyclic voltammograms of the chromium (III) complex exhibit three pairs of oxidation/reduction waves with negative ε0`values. These waves were assigned to two molybdenum-centered single electron redox processes and one tungsten-centered two electrons process. A positive shift of these waves when going from Dawson monolacunary complex to its Cr(III) complex. A modified Dawson structure was inferred from the results for the new chromium (III) complex, in which the chromium and molybdenum atoms are located to the same cap of the anion.

Keywords: polyoxometalate, Dawson structure, chromium, FT-IR spectroscopy, UV-Vis spectroscopy, NMR-spectroscopy, EPR-spectroscopy
  
         
     
         
         
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