The vibrational spectra of the cyanide ligand revisited: the ν(CN) infrared and Raman spectroscopy of Prussian blue and its analogues



A careful analysis of the Raman spectra of the M′x[M(CN)6]y Prussian blue species has enabled a general model for the interpretation of the ν(CN) vibrational spectra. The spectral patterns are derived from those of the metal ions with local Oh symmetry. Two limiting models are discussed. A ‘localized mode’ model, involving matrix-isolated species, is in much better accord with the observations than a ‘factor group’ model. The use of the infrared feature as fingerprint of specific M[BOND]CN[BOND]M′ units arises from the axis-specific nature of individual T1u modes. The interpretation of the A1g and Eg Raman features is done in terms of localized vibrations, with involvement of additional energy terms from the lattice motions. Copyright © 2011 John Wiley & Sons, Ltd.