The crystal and molecular structure of sodium pentacyanoammineferrate(II) heptahydrate. Role of intermolecular hydrogen-bond interactions

The crystal and molecular structures of sodium pentacyanoammineferrate(II) heptahydrate have been determined by X-ray diffraction. The FeN distance is longer than in the analogous iron(III) complex by 0.06 Å; the FeC and CN distances are similar to those for the hexacyanoferrate(II) species, although with a significant relative shortening of the trans FeC bonds. The anions display a chain-like arrangement, with interlinking sodium ions and water molecules H-bonded to cyanide N atoms. By comparing with related structures of pentacyano-L-ferrate(II) ions (L=NO+, CN−), it results that the binding mode of the L ligand influences strongly both the first- and second-sphere metal–ligand interactions.