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)] x 2 H(2)O (1) and Cr(3)[Cr(CN)(6)](2) x 10 H(2)O (2) affords two new microporous magnets: CsNi[Cr(CN)(6)] (1d) and Cr(3)[Cr(CN)(6)](2) x 6 H(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.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.