Raman and Infrared Spectra of Transition Metal Halide Hexahydrates

Abstract

The Raman and infrared spectra of NiCl$_2$·6H$_2$O, NiCl$_2$·6D$_2$O, CoCl$_2$·6H$_2$O, CoCl$_2$·6D$_2$O and CoBr$_2$·6H$_2$O single crystals have been measured in the range 3600–30 cm$^{-1}$ (Raman) and 3800–400 cm$^{-1}$ (IR). The water internal modes have been best assigned for NiCl$_2$·6H$_2$O, including Fermi resonance effects. The corresponding Raman intensities have been interpreted in terms of the free molecule Raman tensors. Among the lattice vibrations, the metal halide and metal‐water stretchings, and also the librations of the $MX_2$·4H$_2$O octahedra, have been identified and assigned.