Abstract
The chemistry of polyoxometalates (POMs) keeps drawing the attention of researchers, since they constitute a family of discrete molecular entities whose features may be easily modulated. Often considered soluble molecular oxide analogues, POMs possess enormous potential due to a myriad of choices concerning size, shape and chemical composition that may be tailored in order to fine-tune their physico-chemical properties. Thanks to the recent progress in single-crystal X ray diffraction, new POMs exhibiting diverse and unexpected structures have been regularly reported and described. We find it relevant to systematically analyse the different equilibria that govern the formation of POMs, in order to be able to establish reliable synthesis protocols leading to new molecules. In this context, we have been able to synthesise the Eu3+-containing silico-molybdo-tungstic dimer, [Eu(α-SiW9Mo2O39)2]13−. We describe the synthesis and characterisation of this new species by several physico-chemical methods, such as single-crystal X-ray diffraction, 183W NMR and electrochemistry.
Highlights
Polyoxometalates (POMs) are oxo-metal clusters in which the metal element M is often in its highest oxidation state (M = WVI, MoVI, VV...)
The dimeric anion [Eu(SiW9Mo2O39)2]13− is built of two monovacant Keggin moieties [αSiW9Mo2O39]8− connected to a central Eu3+ cation (Figure 1A)
The Mo and W centres are localised in the structure, the two MoO6 octahedra belonging to two different trinuclear fragments and sharing a corner
Summary
Upon modulating the experimental conditions and selecting the nature of the metal elements and their molar ratios, the different substitution and addition reactions involving POM entities with respect to metal cations offer a wide range of possibilities regarding the synthesis of new molecules which may find applications in a variety of fields such as medicine [3,4], catalysis [5,6], nanotechnologies [7,8], magnetism [9,10], etc It is, possible and more and more common to synthesise POM species that include in their structures some elements specially selected in order to impart the features required for certain targeted applications. Formation constants of this complex had already been calculated by Choppin et al [30], but this is the first time that the compound has been isolated and characterised
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