The Mössbauer effect and chemistry. Part VI. Mössbauer spectra, paramagnetic susceptibilities, and electron paramagnetic resonance measurements for three iron(III) compounds of type FeCl(β-diketonate)2

Abstract

The Mössbauer spectra of FeCl(R¹CO·CH·COR²)₂(R¹= R²= Me; R¹= Me, R²= Ph; and R¹= R²= Ph) have been measured at temperatures between 300 and 1·7 K and in external magnetic fields. In zero field, the spectra consist of a quadrupole split pair of lines. The relative heights of these lines become equal only as the temperature approaches absolute zero. This behaviour is interpreted as arising from zero-field splitting of the sextet ground-state with the parameter D positive. Both the quadrupole splittings and the chemical isomeric shifts are typical of high-spin iron(III) complexes. Although all three compounds obey the Curie–Weiss law with very small θ values down to 80 K, only FeCl(PhCO·CH·COPh)₂ behaves as a simple paramagnet at 4·2–1·7 K. The other compounds show evidence of intramolecular antiferromagnetism involving a pair-wise interaction. E.s.r. measurements on FeCl(MeCO·CH·COMe)₂ showed a broad resonance with an isotropic g of 4·22.