Co₃[Co(CN)₅]₂:  A Microporous Magnet with an Ordering Temperature of 38 K

The reaction between [Co(H2O)6]2+ and [Co(CN)5]3- in deoxygenated water yields a dark blue solid of composition Co3[Co(CN)5]2.8H2O (1). X-ray powder diffraction data indicate a cubic Prussian blue-type framework, wherein the hexacyanometalate positions have only a two-thirds occupancy of square-pyramidal [Co(CN)5]3- units. Upon dehydration, the compound retains crystallinity and exhibits a Type I dinitrogen sorption isotherm, characteristic of a microporous solid. Magnetic measurements show 1 to behave as a ferrimagnet with an ordering temperature of 48 K, which is reduced to 38 K in the dehydrated solid. At 5 K, both 1 and dehydrated 1 exhibit magnetic hysteresis with a coercive field of 1160 G (the highest value yet reported for a cubic Prussian blue analogue) and remnant magnetizations of 1540 and 745 cm3G/mol, respectively. Thus, dehydrated 1 represents the first compound for which microporosity and long-range magnetic ordering have been demonstrated to coexist.