Synthesis and Characterization of New Rare‐Earth Sandwich‐Type Tungstoarsenates

Two new sandwich‐type tungstoarsenate complexes [{Ln₃O₃(OH₂)₂}(AsW₉O₃₄)₂]¹⁵⁻ (Ln=La, Ce) were synthesized and studied using spectroscopy and cyclic voltammetry. Ion‐exchange experiments provided evidence for covalent, inner‐sphere bonding of the rare‐earth cations to the trilacunary [AsW₉O₃₄]⁹⁻ polyoxometalate. Cyclic voltammograms of [{Ln₃O₃(OH₂)₂}(AsW₉O₃₄)₂]¹⁵⁻ exhibited two pairs of waves with negative potential values, which were attributed to the W^VI/W^V redox processes in the polyoxotungstate framework. Redox studies of the cerium derivative revealed the presence of two types of cerium ions.

Keywords:

• polyoxometalates
• heteropolyoxometalates
• rare‐earth elements
• tungstoarsenates

This work was partially funded by a Greek‐Romanian bilateral cooperation project, and A.R.T. is grateful to the GSRT (Greece) and MER (Romania) for financial support.