Hyperfine and magnetic properties of 19e− (electron reservoir) sandwiches of Fe(I), C5R5FeC6R6 (where R=H or CH3) and (C6(CH3)6)2Fe+: Mössbauer experiments and molecular orbital calculations

Abstract

The four compounds C5H5FeC6H6, C5H5Fe(CH3)6, C5(CH3)5FeC6(CH3)6 and (C6(CH3)6)2Fe+ were studied by Mossbauer spectroscopy on powders. On the basis of semi-empirical molecular orbital calculation (Iterative Extended Huckel with self-consistence of the charge) in which parameters derived from X-ray data are used, we have modelized the thermal behaviour of the electric field gradient (EFG) tensor from 4 K to 300 K. The reduction in magnitude of electronic observables (e.g. spin orbit coupling constant and EFG magnitude) gave evidence for a dynamic Jahn-Teller effect. Spectra in a high magnetic field (6 teslas) confirmed the paramagnetic behaviour of the compounds. The sign of the EFG tensor, the magnetic hyperfine field tensor and its orientation with respect to the EFG tensor were determined.