Effects of Interionic Coupling on the Electronic Spectra of Transition Metal Ions. The Ligand Field Spectra of CsNiCl3 and CsNiBr3

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Abstract
The polarized crystal spectra of CsNiCl3, CsNiBr3, and nickel(II) doped into the isostructural magnesium salts, CsMgCl3 and CsMgBr3, have been investigated in the near infrared and visible region. The spectra can be satisfactorily interpreted using the Liehr and Ballhausen ligand field model for a d8 system in an octahedral environment. The intensities of the allowed, triplet→ triplet, transitions are essentially independent of nickel ion concentration and show the temperature dependence expected of a vibronic mechanism. On the other hand, the oscillator strengths of certain spin forbidden, triplet→ singlet, bands show a strong concentration dependence. These transitions are more intense in the spectra of the pure salts suggesting that their intensities are increased by exchange interactions between nickel ions. The intensity behavior of the multiplicity forbidden transitions in the nickel compounds is similar to that observed for a number of high spin manganese (II) salts.