Molecular dynamics study of ferrocene topology under various temperatures

We present the first quantum mechanical Atom-Centered Density-Matrix Propagation molecular dynamic (MD) study to investigate ferrocene (Fc) conformation in gas phase. The MD simulations were performed at several temperatures (7, 18, 80, 120, 180, 293, and 500 K) for a period of 10 ps. It is found that, at very low temperatures (≤18 K), ferrocene prefers eclipsed-like conformation. At higher temperatures (>18 K), the cyclopentadienyl rings (Cp) of ferrocene exhibit apparent fluxional rotations, leading to configurations with the rotational angle δ distributing within a range of 0° (eclipsed) to 18° (approximately half of 36° for the staggered conformation), accompanied by the cyclopentadienyl ring tilt up to approximately 12° at 500 K. The simulated mean inferred (IR) spectrum of ferrocene at 7 K is clearly dominant by a doublet-splitting band of eclipsed-like Fc features in the region of 400 to 600 cm−1, in agreement with previous IR studies. The animation obtained from the MD simulations indicates that, at room temperature, the Fe-C distances in ferrocene are in fact not strictly congruent but 2:2:1-fold.