Dynamische <i>Jahn‐Teller</i> Verzerrungen und chemische Bindungsverhältnisse in orbitalentarteten Sandwichkomplexen

Abstract

Abstract In order to derive information on the Jahn ‐ Teller effect and on chemical bonding in orbitally degenerate sandwich molecules, the low‐spin d 5 ( 2 E 2g ) metallocenes Mn(cp) 2 and Fe(cp) as well as the d 7 ( 2 E 1g ) metallocenes Co(cp) 2 and Ni(cp) have been diluted in a variety of diamagnetic host systems and studied by ESR. at liquid helium temperature and slightly higher temperatures. Analysis of the measured anisotropic Zeeman and hyperfine data leads to the conclusions that the Jahn ‐ Teller distortions remain entirely dynamic in all four cases (E JT ≲ h v ), and that the covalent delocalization of the singly occupied degenerate metal 3d orbital over the ligand rings correlates well with the observed Jahn ‐ Teller distortion increasing strongly along the series Fe(cp) &lt; Mn(cp)&lt; 2 &lt; Co(cp) 2 &lt; Ni(cp) . This finding agrees with the expectation that the ligand components of the singly occupied e 2g (e 1g *) orbitals are mainly responsible for the dynamic e 1g (e 2g ) distortions in the cyclopentadienyl rings.