Octacarbonyl Diiron. A Density Functional Study

The electronic and molecular structures of several isomers of the
title compound have been studied by
approximate density functional theory. A geometric arrangement
with two bridging CO ligands was identified as
the most stable structure, similar to that of
Co2(CO)8. However, the terminal CO
ligands in Fe2(CO)8 adopt a
staggered
rather than an eclipsed arrangement. The unbridged isomer is shown
to be stabilized by a trans bent distortion. The
CO stretching frequencies are reported for the most stable isomers.
The theoretical findings are compared to the
experimental studies on Fe2(CO)8. A
mechanism for the isomerization reaction of the dibridged structure to
the
unbridged structure is proposed.