Generation and O2 Adsorption Studies of the Microporous Magnets CsNi[Cr(CN)6] (Tc=75 K) and Cr3[Cr(CN)6]2•6H2O(TN=219 K)

Dehydration of the Prussian blue analogues CsNi[Cr(CN)6]center dot 2H(2)O (1) and Cr-3[Cr(CN)(6)](2)center dot 10H(2)O (2) affords two new microporous magnets: CsNi[Cr(CN)(6)] (1d) and Cr-3[Cr(CN)(6)](2)center dot 6H(2)O (2d). Compounds 1d and 2d maintain the Prussian blue structure, and N-2 adsorption measurements at 77 K show them to be microporous with BET surface areas of 360 and 400 m(2)/g, respectively. Both solids largely retain the magnetic properties of their parent hydrates, with 1d ordering at 75 K and 2d ordering at 219 K, by far the highest ordering temperature yet observed for a microporous magnet. The compounds further show unexpected changes in their magnetic properties upon adsorption of O-2. In 2d, adsorption of O-2 results in a reversible decrease in the magnetic moment of the system, as well as a reduction of the coercivity from 110 to 10 G and of the remnant magnetization from 1200 to 400 emu center dot G/mol, indicating a net antiferromagnetic interaction between O-2 and the framework. In 1d, adsorption of O-2 instead results in a reversible increase in the magnetic moment of the system, indicating a net ferromagnetic interaction between O-2 and the framework. Together, the results suggest that ferromagnetic exchange coupling between O-2 and the [Cr(CN)(6)](3-) units provides the predominate magnetic interaction of the adsorbate with the framework.