Bonding in ‘closed,’ open, and half-open ferrocenes: new insight from structural and Mössbauer spectroscopic studies

A 17 electron edge-bridged open metallocene, bis(6,6-dimethylcyclohexadienyl)iron cation, which had previously been observed electrochemically, has been isolated and characterized. Mössbauer spectroscopic data have been obtained for this compound, and for various neutral 18 electron open, half-open, and ‘closed’ ferrocenes, and are in accord with the previous indications that much greater metal–ligand orbital mixing occurs for pentadienyl, as opposed to cyclopentadienyl, ligands. Pertinent structural data have also been obtained for Fe(C5H5)(2,4-C7H11) and Fe(c-C7H9)2 (C7H11=dimethylpentadienyl; c-C7H9=cycloheptadienyl) in order to aid in comparisons between metal–pentadienyl and metal–cyclopentadienyl bonding.