Low temperature magnetic and Mössbauer studies on anhydrous iron(II) sulfonates

Magnetic susceptibilities from 130 to 4.2 K are reported for a series of Fe(RSO3)2 compounds, where R is F, CF3, CH3, and p-CH3C6H4. The β form of Fe(CH3SO3)2 exhibits a maximum in susceptibility at approximately 22.5 K and a sharp drop in susceptibility below the maximum indicating a transition to a magnetically ordered state. None of the other compounds exhibit magnetic ordering although abnormally low magnetic moments down to 2.0 K are observed for α-Fe(CH3SO3)2. Variable-temperature Mössbauer studies on Fe(CF3SO3)2 and β- and α-Fe(CH3SO3)2 are reported and the magnitude of axial field splitting is estimated for these compounds. The first two have trigonally elongated FeO6 chromophores, whereas the third is trigonally compressed. The nature of the distortion in α-Fe(CH3SO3)2 is confirmed by magnetic perturbation Mössbauer studies. Spectra in applied fields of 4.50 and 5.63 T show a doublet–triplet pattern, with the triplet at higher energy, indicating a negative Vzz and an orbital singlet ground state.