On the crystal structures of some nickel hexacyanoferrates (II,III)

The crystal structures of some nickel hexacyanoferrates (II, III), including mixed compositions containing Na+, K+ and Cs+, were resolved and refined from XRD powder patterns. Data from infrared, Mossbauer and adsorption techniques provided complementary structural information. The crystal structures of Ni-3[Fe(CN)(6)](2)center dot 16H(2)O and NiCS2[Fe(CN)(6)] were refined in space group Fm3m. NiNa2[Fe(CN)(6)]center dot 2H(2)O and NiK2[Fe(CN)(6)]center dot 2H(2)O were found to be orthorhombic (space group Pmn2(1)). This structure (Pmn21) results from a distortion around the alkali ion, which appears as a monohydrated interstitial species. On ionic exchange in an aqueous solution containing Cs+, the orthorhombic distortion disappears and the cubic cell is obtained. Cs+ is a large cation and space is not available for interstitial water molecules. This orthorhombic model is also supported by the Mossbauer spectra of the ferrous analogs, FeK2[Fe(CN)(6)]center dot xH(2)O and Fe[Pt(CN)(6)]. (c) 2004 International Centre for Diffraction Data.