Cluster-expanded Prussian blue analogues

A method for expanding the pores in crystalline frameworks is demonstrated with the substitution of face-capped octahedral [Re(6)Q(8)(CN)(6)](4-) (Q = Se, Te) clusters into the Prussian blue structure. The clusters react in aqueous solution with Ga3+ and Fe3+, respectively, to precipitate Ga-4[Re6Se8(CN)(6)](3). xH(2)O and Fe-4[Re6Te8(CN)(6)](3). xH(2)O. Rietveld analysis of X-ray powder diffraction data for the former compound confirms the expanded crystal structure, which features large water-filled cavities more than twice the volume of those in Prussian blue. The new materials can be dehydrated without loss of integrity, and maintain crystallinity at temperatures up to 250 or 300 degrees C, further, the increase in void volume is shown to significantly enhance their capacities as molecular sieves and enable absorption of larger alcohol molecules such as ethanol and n-propanol. A soluble form of the black iron-containing phase exhibits a cluster-to-metal charge-transfer band at 736 nm, slightly lower energy than the metal-to-metal charge-transfer band responsible for the color of Prussian blue.