The complex is tricarbonyl(η⁴-cyclobutadienyl)iron(0). The η⁴ hapticity means the cyclobutadienyl ligand is bonded to the iron center using all four of its carbon atoms in a planar, side-on fashion. This bonding mode is characteristic for antiaromatic rings like cyclobutadiene, which form stable complexes with metals. The iron is in the 0 oxidation state. The three carbonyl (CO) ligands are terminal. The correct structure must show the Fe(CO)₃ unit coordinated to the flat, square cyclobutadiene ring, not edge-bound or through a single carbon.

Final Answer: The first structure is correct.