Electronic Conductivity in a Porous Vanadyl Prussian Blue Analogue upon Air Exposure

Exposure to humid O₂ or ambient air affords a 5-order-of-magnitude increase in electronic conductivity of a new Prussian blue analogue incorporating Co^II and V^IV-oxo units. Oxidation produces a mixed-valence framework, where the O₂ exposure time controls the V^IV/V^V ratio and thereby the material's conductivity. The oxidized framework shows an intervalence charge-transfer band at ca. 4200 cm^-1, consistent with mixed valence. The mixed-valence frameworks show semiconducting behavior with conductivity values of 10^-5 S·cm^-1 at room temperature and 10^-4 S·cm^-1 at 100 °C and activation energies of ca. 0.3 eV. N₂ adsorption measurements at 77 K show that these materials possess permanent porosity before and after oxidation with Brunauer-Emmett-Teller surface areas of 340 and 370 m²·g^-1, respectively.