The discoverers were reluctant to assert an oxidation state of the iron centers in the compound, instead deferring the details of the electronic structure to computational studies.
The crystal structure reveals that the three iron centers arrange in an equilateral triangle (nearly ideal; Fe1 = 59.67°, Fe2 = 60.15°, and Fe3 = 60.18°) The corresponding bond lengths are similar to one another, (Fe1–Fe2 = 2.829 Å, Fe1–Fe3 = 2.815 Å, and Fe2–Fe3 = 2.830 Å), and reflective of Fe-Fe single bonds. As a trinuclear cluster, it would be thought to have a stable 48-electron closed-shell configuration (24 electrons from the three iron atoms and 24 electrons from the three COT rings).
In the original depiction, each COT ligand acts as an η and η donor, and thus, some degree of π-allylic and pentadienyl bonding modes can be inferred – though the degree of metal-to-ligand electron transfer is uncertain. Computational models suggest the binding mode to lie between η and η, as small shifts in geometry make each mode effectively equivalent (see section on fluxional behavior). Furthermore, DFT calculations with the BLYP functional using a TZP basis set for iron and DZP for carbon and hydrogen estimate a Hirshfeld charge of 0.08 on the iron centers (and Voronoi deformation density of 0.00). Interestingly, all of the bond orders of the C-C ring lie between 1.26 and 1.33, sharply contrasting the discrete single and double bonds of free cyclooctatetraene, or COT complexes with non-bound olefins.
Doubly reduced COT (dianion) is known to adopt a planar (aromatic) comformation to metal centers, which is not observed in Fe(COT). However, arguments also exist that such comformations are more related to binding efficiency than aromaticity.
In computational studies (BP86), when Fe(CH) is optimized as a singlet (gas phase), the iron centers are arranged in an ideal equilateral triangle, as experimentally observed in the crystal structure. In such an electronic configuration, each iron atom achieves an 18-electron configuration through pseudo η and η coordination to alternating COT ligands. However, if the compound is optimized as a triplet structure, the iron centers instead are a scalene triangle, featuring significant Jahn-Teller distortions.
Additional NBO analysis of the singlet structure reveals Wiberg Bond Indices of 0.22 for the Fe-Fe bonds, closely reminiscent of that of D Fe(CO) (0.18).