Moessbauer spectroscopy of organometallic compounds. Isomerism in [(.pi.-C5H5)Fe(CO)2]2SnCl2 and related molecules

Abstract

The Mossbauer spectra of a number of organotin compounds derived from [π-C5H5Fe(CO)2]2 have been examined at liquid nitrogen temperature, using both the 14.4-keV resonance γ radiation of 57Fe and the 23.8-keV resonance γ radiation of 119Sn. These measurements show that for (π-C5H5)Fe(CO)2SnCl3 and (π-C5H5)Fe(CO)2Sn(C6H 5)3 there are no observable conformational changes on dissolution of the crystalline solids in solvents which set to a glassy matrix at low temperatures. The 57Fe Mossbauer parameters in [(π-C5H5)Fe(CO)2]2SnCl 2 and [(π-C5H5)Fe(CO)2]2GeCl 2 are found to be invariant with respect to dissolution, and from these data it is concluded that the anomalous bond distances and bond angles, derived from the X-ray diffraction data for these compounds, arise from the specific bonding interactions within the molecule, and not from stacking forces between molecules in the crystalline state. The 119Sn Mossbauer spectra and infrared data for [(π-C5H5)Fe-(CO)2]2SnCl 2, moreover, show the existence of two structural forms in solution, and these are identified with the two possible rotational isomers obtained by rotation of the metal-metal bond. On the basis of isomer shift systematics, an assignment of the parameters to the two forms can be made.