Parameters and form of the Mossbauer spectra of iron(III) beta-diketonates: New data

Mossbauer spectra have been measured at 295 and 78 K for ten Fe-57-enriched iron(III) beta -dikeronates differing bt the type of radical in the chelat e ring. Since the literature data for compounds of this class are incomplet e and contradictory, a repeated analysis of spectrum shape and parameters h as been performed. The chemical shift and quadrupole splitting are virtuall y independent of the type of radical in the chelate ring whereas the line w idth and asymmetry exhibit a pronounced dependence on the temperature and c omposition of the compounds. The available concepts on the nature of quadru pole splitting and relaxation mechanisms determining the lineshape for the given compounds are refined. It is concluded that electron spin relaxation is "longitudinal" or "transverse" relative to the principal axis of the ele ctric field gradient in different compounds.