Theoretical study of negatively charged Fe(-)-(H2O)(n ≤ 6) clusters

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Physical Chemistry

Background:

• Understanding the hydration of metal ions is crucial in various chemical and biological processes.
• The behavior of anionic metal clusters differs significantly from their cationic counterparts, yet is less explored.
• Investigating gas-phase interactions provides insights into fundamental bonding principles without solvent interference.

Purpose of the Study:

• To investigate the structural and energetic properties of gas-phase iron anion-water clusters (Fe(-)-(H2O)n).
• To elucidate the nature of bonding interactions between the Fe- anion and water molecules.
• To compare the hydration behavior of Fe- anions with that of traditional transition metal cations.

Main Methods:

• Density Functional Theory (DFT) calculations were employed.
• All-electron calculations utilized the B3LYP functional.
• The 6-311++G(2d,2p) basis set was used for Fe, O, and H atoms.

Main Results:

• Metal-hydrogen bonding is dominant over metal-oxygen bonding in Fe(-)-(H2O)n clusters.
• Low-symmetry structures are formed, with water molecules attaching via hydrogen atoms.
• Water molecules form three- to six-membered rings bonded to the Fe- anion, which is positioned at the cluster surface.
• Internal isomers exist within a small energy range (3-5 kcal/mol) for n=2-6.
• These findings contrast with high-symmetry structures observed in cationic metal-water complexes.

Conclusions:

• The Fe- anion exhibits a strong capability for water molecule adsorption, forming stable clusters.
• Hydration is driven by Fe(δ-)-H(δ+) interactions and hydrogen bonding networks.
• The bonding and structural characteristics of anionic iron clusters differ markedly from those of cationic transition metal complexes.