Synthesis and Characterization of Ruthenium and Iron-Ruthenium Prussian Blue Analogues

The electronic spectra, electrical conductivity, magnetism, and gas adsorption properties of the newly prepared Prussian blue analogues Fe4[Ru(CN)6]3 · 18H2O (2) and K1.2Ru3.6[Ru(CN)6]3 · 16H2O (3) are compared with those of Prussian blue itself (Fe4[Fe(CN)6]3 ·14H2O, 1). The increase in the degree of electronic localization for the unsymmetrical iron-ruthenium analogue 2 is reflected in a shift of the intervalence charge transfer (IVCT) band to higher energies and an increase in the electrical resistivity. In contrast, the all-ruthenium analogue 3 exhibits a lower-energy IVCT band, as well as the highest electrical conductivity, due to the combined effects of electronic delocalization and the presence of potassium ions. Unlike Prussian blue, the ruthenium and iron-ruthenium analogues show no magnetic ordering transition above 1.8 K. Nitrogen adsorption measurements at 77 K show the dehydrated forms of 2 and 3 to be microporous with BET surface areas of 670 and 325 m2/g, respectively.