Synthesis and characterisation of two new lanthanide sandwich-type heteropolyoxometalates

摘要

The sodium and cesium salts of two new heteropolyoxometalate complexes [{Ln(3)O(3)(OH2)(2)}(PW9O34)(2)](15-) were synthesized and studied using spectroscopy and cyclic voltammetry. The stoichiometry of the trilacunary Keggin 9-tungstophosphate reaction with Ln(III) ions was determined with the aid of conductometric titrations of aqueous solutions. Ion-exchange as well as ES-NIS experiments provided evidence for covalent, inner-sphere bonding of lanthanide cations to the trilacunary alpha-[PW9O34](9-) heteropolyanion. Cyclic voltammograms of [{Ln(3)O(3)(OH2)(2)}(PW9O34)(2)](15-) exhibited two pairs of reduction/oxidation waves with negative half-wave potential (E-1/2) values. These waves were attributed to redox processes corresponding to the polyoxotungstate framework. The redox processes of the Ce derivative revealed the presence of two types of cerium ions. (C) 2003 Elsevier Ltd. All rights reserved. [References: 41]