Bonding in 'closed,' open, and half-open ferrocenes: new insight from structural and Mossbauer spectroscopic studies

A 17 electron edge-bridged open metallocene, bis(6,6-dimethylcyclohexadieny l)iron cation, which had previously been observed electrochemically, has be en isolated and characterized. Mossbauer spectroscopic data have been obtai ned for this compound, and for various neutral 18 electron open, half-open, and 'closed' ferrocenes, and are in accord with the previous indications t hat much greater metal-ligand orbital mixing occurs for pentadienyl, as opp osed to cyclopentadienyl, ligands. Pertinent structural data have also been obtained for Fe(C5H5)(2,4-C7H11) and Fe(c-C7H9)(2) (C7H11 = dimethylpentad ienyl; c-C7H9 = cycloheptadienyl) in order to aid in comparisons between me tal-pentadienyl and metal-cyclopentadienyl bonding. (C) 2001 Elsevier Scien ce B.V. All rights reserved.