Fe13 Cluster Research Articles

High-Spin and Reactive Fe13 Cluster with Exposed Metal Sites.

Atomically defined large metal clusters have applications in new reaction development and preparation of materials with tailored properties. Expanding the synthetic toolbox for reactive high nuclearity metal complexes, we report a new class of Fe clusters, Tp*4 W4 Fe13 S12 , displaying a Fe13 core with M-M bonds that has precedent only in main group and late metal chemistry. M13 clusters with closed shell electron configurations can show significant stability and have been classified as superatoms. In contrast, Tp*4 W4 Fe13 S12 displays a large spin ground state of S=13. This compound performs small molecule activations involving the transfer of up to 12 electrons resulting in significant cluster rearrangements.

Adsorption of SO, CO, O2, and N2 on the most stable small Fe clusters

Electronic, structural, and magnetic properties of small Fen aggregates with n < 15 atoms were investigated in the framework of the density functional theory (DFT). Our results indicate that spin–orbit coupling has little effect on the structural properties. The magnetic moment of each atom in the cluster is greater than the magnetic moment of their bulk material and the average binding energy value rises monotonically with the size of the cluster and approaches the bulk value. As well as Fe7 and Fe13 are the two first magic numbers in good agreement with experimental reports. We studied the adsorption of diatomic SO, CO, O2, and N2 molecules on the Fe7 and Fe13 nanoclusters. The most stable adsorption sites, binding energies, and the effect of adsorption on the electronic properties of the Fe clusters were studied. The different aspects of the adsorption mechanism were also investigated. The interaction intensity order is SO, O2, CO, and N2, and the bond length of the molecules increased after adsorption. X@Fe13 (X = SO, O2, CO, and N2) systems represent higher magnetization compared to the X@Fe7 systems. The maximum effect of absorption on the magnetization of the Fe13 cluster was about 2.4% and on the Fe7 cluster was about 9.6%. These results provide insights into the application of iron-based catalysts and the understanding of the real reactions and experimental reports.

Effects of electrostatic neutralization of Keggin Fe13 on the removal of micro and nano plastic.

The successful preparation and identification of Keggin-structure Fe13 clusters in recent years further enriched the potential application scenarios of ferric coagulants. Comparing the coagulation efficiencies and mechanisms of Fe13 in the removal of nano/microplastics with conventional polymeric Al13 and monomeric Al/Fe, this work aimed to elucidate the coagulation behaviour of Fe13 compared with the traditional mono ferric coagulant, which has the coagulation applied bottleneck of quick and violet hydrolysis. The results showed that Fe13 has a similar electrostatic neutralization potential to Al13, which could keep a positively charged species, especially in acid conditions. The Fe13 species has a selective removal potential toward the microplastics with a polar functional group like ester. Moreover, Fe13 could hydrolyze to form active sol-gel hydroxides in neutral and alkalinity conditions, which is like the behaviour of traditional monomeric Fe coagulants but seldom restabilization. The electrostatic neutralization of Fe13 could enhance the removal of nano plastic from -25-75% compared with monomeric Fe at pH 4. The higher floc density as a monomeric Fe coagulant and better electrostatic neutralization potential of Keggin Fe13 posed a good prospect for Fe13 to replace the monomeric Fe coagulants in conventional coagulation.

Magneto-volume effect in Fe n Ti13–n clusters during thermal expansion

Ab initio molecular dynamics calculations have been carried out to search for the ground state structure of Fe n Ti13–n clusters and measure the thermal expansion of Fe n Ti13–n . The volume of Fe n Ti13–n clusters during thermal expansion is jointly determined by anharmonic interaction and magneto-volume effect. It has been found that Fe6Ti7, Fe9Ti4, Fe11Ti2, and Fe13 clusters can exhibit the remarkable magneto-volume effect with abnormal volume behaviors and magnetic moment behaviors during thermal expansion. A prerequisite for the magneto-volume effect of Fe n Ti13–n clusters during thermal expansion has been revealed and the magnitude of the magneto-volume is also approximately determined. Furthermore, the magneto-volume behaviors of Fe n Ti13–n clusters are qualitatively characterized by the energy contour map. Our results shed light on the mechanism of the magneto-volume effect in Fe n Ti13–n clusters during thermal expansion, which can guide the design of nanomaterials with zero expansion or even controllable expansion properties.

Invar Effect of the Fe13 Cluster.

The Invar effect, which refers to magnetic alloys having an anomalously small thermal expansion, has been under extensive investigations over the past century. However, study on the thermal expansion of clusters and their Invar effect is still lacking. In this letter, we calculate the thermal expansion properties of Fe13-nNin (n = 0, 3, 6, 9, 12, 13) clusters and find that the Fe13 cluster has an abnormally small thermal expansion, which is due to its remarkable magneto-volume effect. It is also revealed that the strong magneto-volume effect of the Fe13 cluster is highly related with the two magnetic states, the same as the interpretation for the Invar effect of a bulk alloy. The anomalously small thermal expansion of the Fe13 cluster is the manifestation of the Invar effect at the cluster scale.

Sequential oxygen chemisorption on Fe13 clusters: from first-principles to practical insights

With the advent of more precise technologies allowing manipulation of matter at nanoscopic scales and novel characterization techniques, a growing field of research is focused on magnetic materials of technical interest—such as Fe clusters—and their related physical-chemical processes. In this study, we present the results of the sequential oxidation process of the Fe13 cluster by considering the physical-chemistry properties of the ground state configurations of Fe13On () clusters. We develop an exhaustive ab initio study into the GGA approach and explore the effect of the chemisorption of oxygen on the structural properties, the chemical stability, the magnetization and the magnetic anisotropy energy (MAE) of the systems. Our results clearly indicate that: (i) one of the studied clusters, Fe13O17, presents the biggest electrophilicity index and the lowest chemical hardness, being the most reactive among the systems studied; (ii) the Fe13O10 exhibits a much more enhanced magnetization than other related clusters intended for health and technology applications (Sun et al 2007 J. Phys. Chem. C 111 4159–63), so that it might be a better candidate for those purposes; and (iii) the MAE presents a complex and intriguing landscape that encourages thinking about the plausible control of magnetic states focused on technical applications.

Ferrihydrite Formation: The Role of Fe13 Keggin Clusters.

Ferrihydrite is the most common iron oxyhydroxide found in soil and is a key sequester of contaminants in the environment. Ferrihydrite formation is also a common component of many treatment processes for cleanup of industrial effluents. Here we characterize ferrihydrite formation during the titration of an acidic ferric nitrate solution with NaOH. In situ SAXS measurements supported by ex situ TEM indicate that initially Fe13 Keggin clusters (radius ∼ 0.45 nm) form in solution at pH 0.12-1.5 and are persistent for at least 18 days. The Fe13 clusters begin to aggregate above ∼ pH 1, initially forming highly linear structures. Above pH ∼ 2 densification of the aggregates occurs in conjunction with precipitation of low molecular weight Fe(III) species (e.g., monomers, dimers) to form mass fractal aggregates of ferrihydrite nanoparticles (∼3 nm) in which the Fe13 Keggin motif is preserved. SAXS analysis indicates the ferrihydrite particles have a core-shell structure consisting of a Keggin center surrounded by a Fe-depleted shell, supporting the surface depleted model of ferrihydrite. Overall, we present the first direct evidence for the role of Fe13 clusters in the pathway of ferrihydrite formation during base hydrolysis, showing clear structural continuity from isolated Fe13 Keggins to the ferrihydrite particle structure. The results have direct relevance to the fundamental understanding of ferrihydrite formation in environmental, engineered, and industrial processes.

Structure and magnetic properties of Fe12X clusters

The electronic and geometrical structures of a Fe12X family of binary clusters Fe12Al, Fe12Sc, Fe12Ti, Fe12V, Fe12Cr, Fe12Mn, Fe12Co, Fe12Ni, Fe12Cu, Fe12Zn, Fe12Y, Fe12Zr, Fe12Nb, Fe12Mo, Fe12Tc, Fe12Ru, Fe12Rh, Fe12Pd, Fe12Ag, Fe12Cd, and Fe12Gd are studied using density functional theory within generalized gradient approximation. It is found that the geometrical structures corresponding to the lowest total energy states found for the Fe12X clusters possess icosahedral shape with the substituent atom occupying the central or a surface site. The only exception presents Fe12Nb where a squeezed cage structure is the energetically most favorable. The substitution of an atom in the Fe13 cluster results in the decrease of its total spin magnetic moment of 44μB, except for Fe12Mn and Fe12Gd. The Fe12X clusters are more stable than the parent Fe13 cluster when X=Al, Sc, Ti, V, Co, Y, Zr, Nb, Mo, Tc, Ru, and Rh.

Exploring CO dissociation on Fe nanoparticles by density functional theory-based methods: Fe13 as a case study

The interactions of CO and of C+O with Fe13 have been studied by the PW91, PW91+U, B3LYP density functional theory-based methods. In each case, various possibilities have been explored for N α –N β . All methods predict an icosahedral structure for the naked particle. Moreover, all density functionals predict CO adsorption on threefold hollow site. Depending on the density functional used, the interaction of CO with the Fe13 cluster induces or not a change in the total number of unpaired electrons and, therefore, of the electronic state. The same situation can appear for the dissociation of adsorbed CO to co-adsorbed C+O. In the most stable configuration, C and O are proximate, bound to a common Fe atom that is oxidized. These results suggest the proper description of the reactivity of magnetic metallic nanoparticles toward dissociation of simple diatomic molecules is likely to involve various spin states, which has implications for the search of the corresponding transition states which cannot be restricted to a single potential energy surface.

Structural Patterns in Carbon Chemisorption on an Icosahedral 2 Iron Cluster

Carbon chemisorption on iron nanoparticles at small carbon coverage has been studied by using a Fe13 particle as a model because it possesses a nearly icosahedral geometry, and complications with additional effects associated with the surface inhomogeneity do not arise. The electronic and geometrical structures of Fe13Cn are computed for n = 0–20 using an all-electron density functional theory with generalized gradient approximation and a rather large basis set. It is found that the energetically preferred structures correspond to the formation of carbon dimers up to Fe13C12 and trimers up to Fe13C18 in octahedral configurations of the dimers and trimers with the Fe13 cluster being endohedral. The trend for the formation of carbon tetramers breaks at Fe13C20. We found that the dependence of the total energy on the total spin is nearly the same for Fe13 and Fe13C8. When the number of chemisorbed carbon atoms exceeds 6, chemisorption quenches the total magnetic moment to 36 μB from the value of 44 μB in the...

Cluster model studies on the electronic and magnetic properties of LaCo13 and La(FexAl1−x)13 alloys

We present studies on both the electronic and magnetic properties of LaCo13 and La(FexAl1−x)13 intermetallic compounds by cluster model calculations within the scheme of density-functional theory. The equilibrium structures of the isolated and embedded clusters, obtained by minimizing the total binding energy, are in good agreement with available experimental data and other theoretical results. The relative stability and formation of LaCo13 and La(FexAl1−x)13 phases have been successfully explained. Interesting changes of magnetic properties in an Al doped Fe13 cluster have been obtained. The possible effect of Al on the magnetic phase diagram of La(FexAl1−x)13 is discussed.