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 O h 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 MCNM′ units arises from the axis‐specific nature of individual T 1 u modes. The interpretation of the A 1 g and E g 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.