Spectroscopic studies of heteropolyanions and their complexes with lanthanide(III) ions

Polyoxometalates (POM) form a unique class of compounds of special properties with wide applications. Chemistry of POM is an important subarea of modern inorganic chemistry. In continuation of earlier work, we present here studies on spectroscopic characterization of POMs and their lanthanide(III) complexes (Ln/POM). A nomenclature system including trivial and systematic names, reflecting information on composition and structure of POM is shortly described. Methods of synthesis of polyanions having inorganic and organic counter cations and results of studies related to POM structure and their Ln(III) complexes are briefly reviewed. Useful techniques for the verification of POMs and Ln/POM compositions and determination of components, including elemental and thermogravimetric analysis, IR and Raman spectroscopy as well as a new spectrophotometric methods for determination of tungsten and molybdenum and for simultaneous determination of these elements in structures POMs and their Ln/POM complexes are presented. An important role of FTIR spectra in characterization of POMs and Ln/POM complexes is shown. Forms of POM complexes such as: sandwiched Ln(POM)2, encapsuled within the cavity of the POM and Ln2POM were studied with the use of absorption spectra (in the Nd(III) hypersensitive band and Eu(III) luminescence spectroscopy). Luminescence (excitation and emission) spectra and luminescence lifetime measurements, recorded for Eu(III) complexes in solid and aqueous solutions at room temperature and luminescence quantum yield of Eu(III) ion were used for characterization of the species. Influence of ionic strength of the complex formation in solution is also presented. The use of EPR method to study magnetic properties and symmetry of the Gd/POM complexes is discussed. Studies show that Gd(III) ion can be useful as a probe to study local environment of the host metal site in terms of symmetry and coordination in Gd/POM. (author)