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Nitroprussides of divalent transition metals form a family of microporous molecular materials. Their properties in this sense depend on the transition metal cation involved and also on the preparative method, which determine their crystal structures. The stable phases of this family of materials belong to one of the following crystal structures: orthorhombic (Pnma) (Mn 2+ , Fe 2+ , Cu 2+ , Zn 2+ , and Cd 2+ ), cubic (Fm3m) (Co 2+ and Ni 2+ ), and orthorhombic (Amm2) (Cu 2+ ). These materials are stable up to above 160°C, while their dehydration takes place around 100°C. On dehydration, Amm2 copper complex changes into a tetragonal (I4mm) phase. The microporous nature of these materials is discussed according to their crystal structure and correlating structural and adsorption data. The accessibility to the pore system was evaluated through adsorption of H 2 O, CO 2 , and N 2 . Pores of both orthorhombic and cubic structures are accessible to H 2 O and CO 2 in experiments carried out at 23 and 0°C, respectively; however, they are inaccessible to N 2 at -196°C. This behavior is discussed as related to the large polarizing power of the nitrosyl (NO) ligand which distorts the local environment of the iron atom and reduces the effective window cross section. The small pores of tetragonal copper nitroprusside were inaccessible to the adsorbates used.

Mn2+and Cd2+form a family of isostructural hexacyanoferrates(II,III). Their crystal structures, including those of mixed compositions containing K+and Cs+as charge balance cations, were resolved and refined from XRD powder patterns. The crystal structures of M3[Fe(CN)6]2⋅xH2O and MCs2[Fe(CN)6] (where M=Mn, Cd) were refined in the space group Fm3m. The mixed salts, MK2[Fe(CN)6]⋅2H2O, were found to be orthorhombic (space group Pmn21). The orthorhombic structure results from a local distortion due to monohydrated potassium ions located in interstitial sites. On ionic exchange in an aqueous solution containing Cs+, the orthorhombic distortion disappears and the cubic cell is obtained. Cs+is a large ion, which practically fills the available interstitial voids stabilizing the cubic structure. In solutions of K+and Cs+the single salts, M2[Fe(CN)6]⋅8H2O (monoclinic P21/n) also transform, in this case liberating M2+ions and forming the corresponding mixed salts. An analogous but slow structural transformation was also observed in the anhydrous forms of these single salts. These structural transformations could be relevant to the use of these compounds as ion exchangers and particularly for the sorption of137Cs+from radioactive waste solutions. The XRD data were complemented with structural information from infrared (IR), Mössbauer and water vapor adsorption techniques. ©2004 International Centre for Diffraction Data.

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Methane adsorption is possible through three types of interactions: (1) dispersive forces (van der Waals type); (2) polarization of its electron cloud by a positive charge center; (3) induced quadrupole moment by perturbation of the molecule electron cloud through the polarization interaction. This induced quadrupole moment is able to interact with the local electric field gradient. Porous Prussian blue analogues and related zeolite‐like zinc hexacyanometallates appear to have unique features for the evaluation of the relative importance of these adsorption forces for the methane storage in molecular porous materials. Methane adsorption isotherms for T3[Co(CN)6]2 (T = Mn, Co, Ni, Cu, Zn, Cd) and Zn3A2[Fe(CN)6]2 (A = Na, K, Rb, Cs) were recorded and interpreted. From the obtained adsorption data information on the relative contribution of both electrostatic and dispersive interactions to the adsorption forces was obtained.