Spectra with tetragonal symmetry

In case of trigonal symmetry, the is not split. However, the orbital degeneracy is lifted by the Jahn-Teller effect which, at higher temperatures, might distort the molecular complex. At lower temperatures, the Jahn-Teller distortion in some cases goes over into a static distortion, and a spectrum due to three magnetic complexes, each with tetragonal symmetry may be observed [53]. 

In D4h (tetragonal) symmetry there is only one unpaired electron in two degenerate orbitals of correct symmetry to give rise to n bonds with a n orbital of the porphyrin moiety [34]. The H NMR spectrum of Fe(protoporphyrin IX)-imidazole-cyanide is reported in Fig. 5.17 [35]. The free rotation of the imidazole ring about the metal-nitrogen bond, which is fast on the NMR timescale, simulates a tetragonal symmetry as far as the chemical shifts are concerned [36]. The four methyls are all downfield, though to a quite smaller value than in the case of... 

The physical mechanisms associated with the phase transition of y-Fe203 nanoparticles induced by laser irradiation have been studied by El MendUi et al., by performing in situ micro-Raman measurements of both as-prepared y-Fe203 nanoparticles (about 4 nm in size) as a function of laser intensity and annealed samples [51]. Raman spectrum for the as-prepared nanoparticles showed the presence of three broad peaks at 350, 500, and 720 cm and magnon mode in the neighborhood of 1,300 cm . Such a Raman spectrum obeys the symmetry rules established for the inverse spinel structure with a tetragonal sublattice distortion,... 

Uranium pentafluoride prepared in the above maimer is the low-temperature, form, which can be identified by its characteristic X-ray powder pattern. The single<rystal structure has been determined tetragonal symmetry, space group I42d(Z = 8), with eight-coordination and a geometry intermediate between a dodecahedron and a square antiprism. Uranium pentafluoride is air sensitive and disproportionates in water to give a precipitate of uranium tetrafluoride and a solution of uranyl fluoride. Consequently, UFs must be handled in an inert atmosphere. The near-infrared-visible spectrum of uranium pentafluoride in acetonitrile has been determined and is perhaps the most convenient characterization. 

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