Differentiation of internal and lattice vibrations in d3 coordination compounds by vibronic spectroscopy. Low frequency vibrations of hexacyanochromate (III) salts

Abstract

The ²E_g→⁴A_2g luminescence spectra of the Cr(CN)^3–₆ ion in crystalline M₃Co(CN)₆(M = K, Rb, Cs, ½Ba) have been measured at 5 K. The spectra in the four hosts are similar in the lattice vibration region (0–220 cm^–1 from the electronic origin) although the infrared spectra of M₃Cr(CN)₆ in the same region are different. The reasons for these similarities and differences are discussed in terms of the lattice dynamics and intensity mechanism for these systems. They provide support for the use of the intensities of vibronic origins as a guide to the contribution that internal coordinates of the complex ion make to the corresponding vibrational motions and for a previous interpretation of the luminescence spectra of the Cr(CN)^3–₆ ion in K₃Co(CN)₆.