Polyoxometalate Monolayers in Langmuir–Blodgett Films

Abstract

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 polyoxoanion [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 [Co4(H2O)2(PW9O34)2]10- and [Co4(H2O)2(P2W15O62)2]16- based on a Co4O16 ferromagnetic cluster, and the polyoxometalates [Co9(OH)3(H2O)6(HPO4)2(PW9O34)3]16- and [Ni9(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, [Na3(NH4)12][Mo57Fe6(NO)6O174(OH)3-(H2O)24]76 H2O.

Effects of film structure on electrochromic properties of the multilayer films containing polyoxometalates

“…Polyoxometalates (POMs) represent a well-known class of structurally well-defined metal oxide clusters with wealthy framework topologies, compositions and possess diverse properties such as catalytic activity, magnetism and luminescence [1][2][3][4][5][6]. POMs are of particular interest in electrochromic material due to their ability to act as an electron reservoir, thereby giving rise to colored mixedvalence state species while retaining their structural integrity [7][8][9][10].…”

Metalloamphiphiles with [Cu2] and [Cu4] Headgroups: Syntheses, Structures, Langmuir Films, and Effect of Subphase Changes

“…In spite of this growing interest, examples of systems bearing discrete [4] multimetallic cores remain rather limited. Only a few mesogens containing flat multinuclear cores [5,6] and a dendrimeric system supporting an iron-sulfur core [7] have been reported.…”

“…Only a few mesogens containing flat multinuclear cores [5,6] and a dendrimeric system supporting an iron-sulfur core [7] have been reported. Recently, we have demonstrated [8] that the use of preassembled carboxylate-based dimers such as copper acetate, formally described as [Cu 2 (OAc) 4 (H 2 O) 2 ], can overcome this constraint. A synthetic strategy was developed to obtain tetrametallic copper complexes containing N 2 O-terdentate open-frame ligands based on 2,6-bis-(iminomethyl)-4-methylphenol, µ 2 -bridging acetates (or benzoates), and µ 4 -oxo groups as coligands.…”

Fabrication and Properties of a Nanocomposite Multilayer Film Based on a Polyoxometalate

“…They show diverse properties such as catalytic activity for chemical transformations, molecule-based conductivity, magnetism, as well as photochromism, electrochromism, and luminescence [1 -13]. One of the most important electronic properties of these structurally well defined polyoxometalate clusters is that they act as electron reservoirs since the reduction products are mixed-valence species with a characteristically deep-blue color ("heteropoly blues") [14,15]. As possible components of electrochromic devices, polyoxometalates (POMs) are promising candidates, also due to their ability to act as an electron reservoir, thereby giving rise to colored mixed-valent species while retaining their structural integrity [1,16,17] [20].…”