Characterization of the structural and electronic properties of binary iron‐carbon clusters composed by six iron atoms and with up to nine carbon atoms was carried out with density functional theory calculations. Neutral, cations (q = +1), and anions (q = −1), some of them experimentally detected, were studied. The formation of dimers and trimers of carbon atoms over the iron surface were preferred. Moreover, some large carbon chains, with up to five atoms, were determined. High spin states emerged for the ground states, with multiplicities above 16, for all clusters independently of the number of carbon atoms attached to the iron core. All neutral clusters were stable because fragmentation (into carbon chains), dissociation (of a single carbon atom), and detachment of all carbons need high amounts of energy. Reactive species were defined by small HOMO‐LUMO gaps. Charge transfer, to the carbon atoms, increased as the carbon content increased, producing, for some cases, an even‐odd behavior for the magnetic moment of the Fe6Cn particles.

The evolution of structural and electronic properties of neutral and charged iron clusters doped with a single carbon atom, Fe n C0,±1 (n = 1–13) series, is studied in this work, which has been carried out throughout all-electron density functional calculations at the BPW91/6-311++G­(2d,2p) level of theory. The results indicate a redshift of the bands in the infrared spectra due to carbon–iron stretching because the cluster contains more iron atoms. The iron–carbon bond lengths and the iron–carbon–iron bond angle increase and the ionization energies decrease as the cluster size increases. Notably, the total spin multiplicity increases smoothly even with the inclusion of the carbon atom. Also, the spin from the additional carbon atom turns parallel in the larger species, contributing to the total magnetic moment. In the Fe6–9,12,13C0,±1 species, the carbon atom becomes tetravalent with a near-planar form. This unusual coordination between carbon and the iron core may be due to the lack of hybridization between the s and p orbitals of carbon and to the large iron–carbon bonds. The nearly straight iron–carbon–iron angles are due to the overlap, in occupied orbitals close to the highest occupied molecular orbital, among pure p orbitals and most of d orbitals of carbon and iron atoms, respectively.

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The chemical activation of the carbon monoxide (CO) molecule on the surface of iron clusters Fe n (n = 1–20) is studied in this work. By means of density functional theory (DFT) all-electron calculations, we have found that the adsorption of CO over the bare magnetic Fe n (n = 1–20) clusters is thermochemically favorable. The Fe n –CO interaction increases the C–O bond length, from 1.128 ± 0.014 Å, for isolated CO, up to 1.251 Å, for Fe9CO. Also, the calculated wavenumbers associated with the stretching modes νCO are decreased, or red-shifted, as another indicator of the CO bond weakening, passing from 2099 ± 4 to 1438 cm–1. Markedly, wavenumbers of vibrational modes νCO agree admirably well in comparison with experimental results reported for Fe n CO (n = 1, 18–20), getting small errors below 2.6%. The C–O bond is enlarged on the Fe n CO (n = 1–20) composed systems, as the CO molecule increases its bonding, charge transference, and coordination with the iron cluster. Therefore, small bare iron particles Fe n (n = 1–20) can be proposed to promote the CO dissociation, especially Fe9CO, which has been proven to obtain the most prominent activation of the strong C–O bond by means of the charge transference from the metal core.