摘要：

The reaction of metallic silver with tungsten tetrachlorideoxide WOCl4 or the reaction of AgCl with WOCl3, both at 690 K, lead to Ag1x[W2O2Cl6] as black lustrous crystal needles. The compound shows a substantial phase field width in the silver content depending on reaction temperature and reaction time and crystals with x = 0, 0.38 and 0.82 were isolated. The crystal structure determinations (monoclinic, C2/m) show the structure to be isotypic to those of Tl[W2O2Cl6] and K0.84[W2O2Cl6] with the presence of 1D polymeric [W2O2Cl6]n strands and Ag+ ions with a variety in the occupation of the respective crystallographic site. Ag1x[W2O2Cl6] represents a mixed valence compound with a variable ratio of W(IV) and W(V) in the W2 dumbbells with a short WW separation of 2.85 . In Fourier maps the electron density of the Ag ion appears smeared over a large area. By structure determinations of stoichiometric Ag1.0[W2O2Cl6] at temperatures of 123, 193, and 293 K a double minimum potential was found with the silver ion dynamically disordered over two flat basins with a thermal activation barrier of 13 meV. No long range ion mobility is present since the Ag+ ions are trapped within a coordinating cage consisting of ten chlorine atoms of the surrounding [W2O2Cl6] strands forming a distorted bicapped cube. By MAS-NMR spectroscopic measurements on the 109Ag nuclei at different temperatures, the spin lattice relaxation times were determined giving a thermally activated barrier of 15 meV. The electronic conductivity of pressed powder samples of Ag[W2O2Cl6] by a four-probe measurement applying direct current is 1 1·cm1 at room temperature and 103 1·cm1 at 25 K. For the conduction mechanism at low temperatures a variable range hopping mechanism is suggested, whereas at higher temperatures a standard semi-conductivity with a bandgap of 60 meV is present.

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