Fe as hydrogen/halogen bond acceptor in square pyramidal Fe(CO)5

Area of Science:

• Computational Chemistry
• Organometallic Chemistry
• Supramolecular Chemistry

Background:

• Iron pentacarbonyl [Fe(CO)5] is a key organometallic compound.
• Understanding non-covalent interactions is crucial in chemistry.
• Previous studies on hydrogen bonds often focused on C-H···O interactions.

Purpose of the Study:

• To theoretically investigate hydrogen-bonded complexes of Fe(CO)5 with HX (X = F, Cl, Br).
• To explore the formation of X-H···Fe interactions and their characteristics.
• To examine the potential for Fe(CO)5 to act as a halogen bond acceptor.

Main Methods:

• Density Functional Theory (DFT) with dispersion correction.
• Atoms in Molecule (AIM) analysis.
• Natural Bond Orbital (NBO) analysis.

Main Results:

• Confirmed X-H···Fe hydrogen bonds with significant red shifts in HX stretching frequencies (~400 cm⁻¹).
• AIM analysis revealed bond critical points and mutual penetration in hydrogen-bonded complexes.
• Fe(CO)5 also forms halogen bonds with ClF and ClH, showing mutual penetration.

Conclusions:

• The X-H···Fe hydrogen bonds exhibit characteristics consistent with hydrogen bonding criteria.
• Charge transfer does not correlate with interaction energy in these systems.
• Determined a 'hydrogen bond radius' for iron (1.60 ± 0.02 Å) and identified Fe(CO)5 as a halogen bond acceptor.