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 Co-2(CO)(8). However, the terminal CO ligands in Fe-2(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 Fe-2(CO)(8). A mechanism for the isomerization reaction of the dibridged structure to the unbridged structure is proposed.