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

摘要

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]_2·16H_O and NiCs_2[Fe(CN)_6] were refined in space group Fm3m. NiNa_2[Fe(CN)_6]·2H_2O and NiK_2[Fe(CN)_6] ·2H_2O were found to be orthorhombic (space group Pmn2_1). This structure (Pmn2_1) 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, FeK_2[Fe(CN)_6]·xH_2O and Fe[Pt(CN)_6].