The $$[(\eta^5-C_5H_5)Fe(CO)_2]_2$$ molecule exists in solution as a 1:1 mixture of cis- and trans-isomers.

At 28°C, ¹H NMR spectrum of the molecule shows

Correct option is A

​Reactions between metal carbonyls and cyclopentadiene usually yield mixed ligand complexes, e.g. Fe(CO)₅ reacts with C₅H₆ to give (η⁵-Cp)₂Fe₂(CO)₄. Two isomers of (η⁵-Cp)₂Fe₂(CO)₄ exist , cis and trans, and both have been confirmed in the solid state. The Fe-Fe bond length (253 pm) is consistent with a single bond giving each Fe centre 18 electrons.

In solution at 298 K, both the cis- and trans-forms are present and the terminal and bridging ligands exchange by an intramolecular process.

The protons of the two cyclopentadienyl ligands in both isomers (cis- and trans-) are chemically equivalent in solution. Both the cis- and trans-isomers lead to identical proton environments for the η⁵-C₅H₅ protons due to the fast exchange between the two isomers, making the proton environments indistinguishable.