Iron–carbon clusters: Geometric structures and interconversions

Synthesis and magnetic properties of sub-nanosized iron carbides on a carbon support

Iron carbide clusters with near-sub-nanometer size have been synthesized by employing a tetraphenylmethane-cored phenylazomethine dendrimer generation 4 (TPM-DPAG4) as a molecular template. Magnetic measurements reveal that these iron carbide clusters exhibit a magnetization–field hysteresis loop at 300 K. The data indicate that these iron carbide clusters are ferromagnets at room temperature.

This study reports the synthesis and ferromagnetism of iron carbide clusters with near-subnanometer size by employing a dendrimer template and carbothermal hydrogen reduction (CHR).

How far away are iron carbide clusters from the bulk?

Combining the basin hopping structure searching algorithm and density functional theory, the iron carbide clusters, Fe_xC_y (x ≤ 8 and y ≤ 8), and clusters with various stoichiometries (Fe_2nC_n, Fe_3nC_n, Fe_nC_2n, Fe_nC_3n and Fe_nC_4n (n = 1-7), Fe_5nC_2n, and Fe_4nC_n (n = 1-5)) are predicted. The stable structures of iron rich carbide clusters are composed of C-C dimers or single C atoms on the surface of the clusters, which are remarkably different from their corresponding bulk structures, where the carbon atoms are atomically distributed in the iron matrix. The most stable carbon rich clusters are highly diverse in topology (bowl, basket, plane, shoe, necklace, etc.) with long carbon chains. The Bader charge analysis shows that the size effect on iron carbide clusters is an electronic tuning. Large carbon-rich clusters appear even under low carbon chemical potentials, whereas small iron-rich clusters are only energetically stable in high carbon chemical potentials, which indicates that changing the carbon chemical potential can tune the morphology (size and stoichiometry) of the iron carbide clusters. These results may help us understand the catalytic activity of iron and iron carbides in reactions such as the Fischer-Tropsch synthesis and the carbon nanotube formation process.

Structural evolution of triniobium carbide clusters: evidence of large Cn chains (n = 3-4) in Nb3Cn- (n = 5-10) clusters

First-principle density functional calculations and photoelectron spectroscopy experiments show that triniobium carbide clusters exist in multiple motifs. The Nb(3)C(n)(-) (n = 5-10) series have isomers surrounding a triangular Nb(3) base while incorporating Nb-C bonding. We provide evidence of not only C(2) carbon chains but also stable isomers with previously unidentified C(3) and C(4) carbon chains in triniobium carbide clusters.