Mossbauer effect studies of alkali metal ferricyanides and hydrogen-bonded ferricyanic acid

Mossbauer spectra of anhydrous ferricyanic acid, H3Fe(CN)6, and alkali metal ferricyanides, M3[Fe(CN)6]. xH2O (where M = Li, Na, Rb, Cs, NH4 and Ag), have been studied at room temperature. These compounds show a two line spectrum indicating definite quadrupole splitting (ΔEQ). The values of ΔEQ range from 0.20 to 0.76 mm/sec. The isomer shifts (δ) vary from 0.08 to 0.26 mm/sec. (relative to sodium nitroprusside dihydrate). The isomer shift shows generally a decreasing trend with the increase in the electronegativity of the substituent cation. It is suggested that the cations influence the π-acceptor property of the cyanide ligands. The s-electron density at the iron nucleus increases as the π-acceptor nature of the ligand increases. The quadrupole splitting data is also consistent with this interpretation. A linear relationship is observed between δ and ΔEQ. The isomer shift for H3Fe(CN)6 is comparatively high presumably due to the presence of intermolecular hydrogen bonding in this compound