Synthesis, characterization of magnesium-substituted tungstoarsenate, , and its electrochromism

The novel, magnesium-substituted tungstoarsenate, [As2W15Mg3O62]18− (As2W15Mg3) (1) has been synthesized from the lacunary precursor [As2W15O56]12− and characterized by elemental analysis, IR, UV and 183W NMR spectroscopy. The 183W NMR spectrum of 1 exhibits three lines of 1:2:2 intensity at −141.17, −147.86 and −183.02 ppm, as expected for the C3v structure of the tri-substituted α-Dawson anion. The electrochemical behavior of 1 in aqueous solution has been investigated. The compound exhibits successive reduction processes of the W atoms in a negative potential range. The compound As2W15Mg3-containing monolayer and multilayer films have been fabricated on ITO substrate with poly(diallyldimethylammonium) chloride (PDDA) by layer-by-layer deposition. Thus-prepared multilayer films were characterized by cyclic voltammetry (CV), UV–vis spectroscopy and X-ray photoelectron spectroscopy (XPS). The electrochemical behavior of the multilayer films shows three reversible two-electron redox waves in acidic aqueous solution in the potential range of 0.4 to −0.7 V, which are same with that in the solutions. The electrochromic behavior of the multilayer films has been studied in situ CV–UV–visible spectroelectrochemical methods, indicating the multilayer films show suitable response times and good reproducibility of response. This study provides a new compound to explore the possibility of application as electrochromism material.