Preparation, electrochemistry and crystal structure of a derivative of 18-tungstophosphate with Dawson structure: K16H[Yb(a-2-P2W17O61)2]·44H2O

The heteropolyanion [Yb(a-2-P2W17O61)2]172 has been isolated as a potassium salt in ,30% yield by five-day decreasing temperatureprogrammed from 60 8C to room temperature, in a potassium acetate buffer, formed by reaction of K6P2W18O62·10H2O with Yb(NO3)3 and characterized by IR, UV spectra. Single crystal X-ray structural analysis of K16H[Yb(a-2-P2W17O61)2]·44H2O (triclinic, space group PI a ¼ 14:499ð3Þ, b ¼ 22:433ð5Þ, c ¼ 24:505ð5Þ A ° , a ¼ 95:36ð3Þ;b ¼ 102:67ð3Þ, g ¼ 100:06ð3Þ8; Z ¼ 2; 24,089 independent reflections, R1 ¼ 0:0497) reveals that two chemically identical [a-2-P2W17O61]102 moieties are connected through one Yb atom, which is in a square antiprismatic coordination environment with eight oxygen atoms, four from each of the two [a-2-P2W17O61]102 moieties. The Yb(III) ion substitutes for two [W ¼ O]4þ units in the ‘cap’ regions of the tungsten–oxygen frameworks of the two parent Wells–Dawson ions. The point group symmetry of the title polyanion is C2. In the extensive pH region from 10.5 to 1.60, the cyclic voltammograms for the title compound in the presence of 0.5 MNaCl aqueous solution as supporting electrolyte mainly illustrate nearly reversible one-electron reduction processes. The results of the thermogravimetric analysis of the title compound show one one-step slow weight loss and the framework decomposition of the polyanion in the title compound is at 560.0 8C. q 2004 Elsevier B.V. All rights reserved