Molecular Structures and Vibrational Frequencies of Iron Carbonyls: Fe(CO)₅, Fe₂(CO)₉, and Fe₃(CO)₁₂

Abstract

Hybrid Hartree−Fock/density functional theory (HF/DFT) explicitly including all electrons has been employed to study the three iron carbonyls Fe(CO)5, Fe2(CO)9, and Fe3(CO)12. The geometries are fully optimized by the BP86 and B3LYP methods in conjunction with two basis sets, including as many as 507 contracted Gaussian functions for Fe3(CO)12. Our theoretical geometries and harmonic vibrational frequencies are carefully compared with available experimental results. For Fe3(CO)12 most of the fundamental vibrational frequencies have never been assigned experimenally. Several of the experimental assignments for Fe2(CO)9 and Fe3(CO)12 are dubious.