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 nu(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 M-CN-M' units arises from the axis-specific nature of individual T-1u modes. The interpretation of the A(1g) and E-g Raman features is done in terms of localized vibrations, with involvement of additional energy terms from the lattice motions. Copyright (C) 2011 John Wiley & Sons, Ltd.