Spectra of tetrahedral complexes of transition metals. Jahn–Teller effect in the tetrabromoferrate(III) ion
Abstract
The single-crystal spectra of RFeBr4(R = 4-ethylpyridinium, Me4N+, Me3NH+, Me2NH2+, and MeNH3+) have been recorded at room temperature and ca.80 K. The fine structure resolvable in one transition has been analysed as vibrational progressions of non-totally symmetric t2 modes. The consequences of this observation are discussed in terms of a Jahn–Teller distortion of the excited electronic state. It is shown that a consistent assignment of the excited states is possible with the aid of a crystal field energy calculation. The spin–orbit splittings of the lowest-lying excited quartet and doublet states are calculated from the Tanabe–Sugano–Schroeder–Tree matrices. It is suggested that the Jahn–Teller effect is responsible for a quenching of the expected spin–orbit splittings. Finally, the spectral differences between the isoelectronic MnBr42– and FeBr4– complexes are discussed.
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