Ten out of eleven Raman active modes were detected in [Ni(NH&] XZ powders, apart from internal modes of the X-ions. The Raman active lattice mode happens to agree fairly well with the predictions of a model based on the electrostatic potential field of point charges. The X=Cl compound showed evidence of losing ammonia during irradiation with the laser beam. Two modes (the N-Ni-N angle deformation and the lattice vibration) are especially sensitive to the NH3-vacancies thus created.
Infra-red and Raman spectra of [Me(NH3)6]Xz crystals were measured for Me = Co, Ni and X-C1, Br, I. BF4, c104, PF6. The bands obtained were interpreted as being connected with vibrations of the [Me(NH3)6] octahedron. A far infra-red band at ca. 80 cm-I was interpreted as an IR active lattice mode. A lattice dynamics model based on electrostatic interactions between point ions was developed. A low frequency Raman active lattice mode was theoretically foreseen by this model.
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