Polyoxometalate monolayers in Langmuir-Blodgett films

Langmuir and Langmuir-Blodgett (LB) films of a variety of polyoxometalates of different shapes, sizes, and charges were prepared by taking advantage of the adsorption properties of these polyanions on a positively charged monolayer of an organic surfactant spread on water. Three different aspects were investigated. 1) The electrochemical and electrochromic properties of LB films containing the easily reducible polyoxoamon [P2Mo18O62](6-). Absorbance changes of these LB films deposited onto an ITO substrate have been induced by repeated switching of the applied potential. These changes are due to the formation of the colored reduced forms of the polyanion. Coloration and bleaching of the LB film occur very quickly and are reversible. 2) The preparation of LB films based on magnetic polyoxometalates, such as the Keggin anions, [CoW12O40](6-) and [SiMn-(OH2)W11O39](6-), or containing magnetic clusters of increasing nuclearities such as [Co-4(H2O)(2)(PW9O34)(2)](10-) and [Co-4(H2O)(2)(P2W15O62)(2)](16-) based on a Co4O16 ferromagnetic cluster, and the polyoxometalates [Co-9(OH)(3)(H2O)(6)- (HPO4)(2)(PW9O34)(3)](16-) and [Ni-9(OH)(3)-(H2O)(6)(HPO4)(2)(PW9O34)(3)](16-) based on a nonanuclear M9O36 cluster. 3) The preparation of LB films of the giant heteropolyoxomolybdate, [Na-3(NH4)(12)][Mo57Fe6(NO)(6)O-174(OH)(3)- (H2O)(24)]center dot 76H(2)O.