Superatomic and adsorption properties of Ni atom doped Au clusters

Planar σ-Aromaticity in Ga-Doped Au Clusters

Recently, the first example of Au-Ga clusters is synthesized and characterized, which can be described by the jellium model as a superatom with 8 valence electrons that come from the joint contribution of Au and Ga atoms, opening a whole new field for further research. Here, the structure features and stability of one Ga-doped Au cluster with magic number electrons (6 and 8) are analyzed in detail. Moreover, the valence electron fillings and chemical bonding of them are also further explored. It is found that Au₃Ga and Au₅Ga clusters present planar configurations, and they have higher stability than that of neighbor clusters. The AIMD simulations show that these two clusters still have a good thermal stability at 500 K. The molecular orbital analyses show that the Au₃Ga and Au₅Ga have three and one typical delocalization orbital throughout the whole planar spaces, respectively, following the planar σ-aromaticity rule. The ELF and LOL analyses are further performed, and the results are consistent with the molecular orbital analyses. The NICSzz-scan curves confirm that the Au₃Ga is more aromatic than the Au₅Ga, and the reason is that the former has more delocalized electrons than the latter. Our work opens up aromaticity studies in the Au-Ga clusters.

The nature of stability and adsorption interactions of binary Au-Li clusters with bridge adsorption structures

Earlier findings have confirmed that CO molecules have propensities to adsorb on low-coordinated gold atoms (top sites) of Au-based clusters, which can be treated by the Blyholder model wherein the σ donation and π-back donation take place. Here, the structural features and stability of (AuLi)_n (n = 1-9) clusters were first analyzed using the GA-DFT method. The new adsorption modes, vibration frequencies and electronic interactions for Au-Li clusters with CO were investigated in detail. More excitingly, we found that CO prefers to adsorb on the bridge sites of the Au-Li clusters rather than on the top sites, which are much lower in energies than the top adsorptions, and the C-O stretching frequencies are also red-shifted. AIMD simulations show that the adsorption structures still have good thermal stability at 500 K. The density of states reveals that the electronic structures of Au-Li clusters have excellent stability for the bridge adsorptions of CO molecules. The ETS-NOCV analysis and NPA charges show that the direction of charge flow is from Au-Li clusters → CO. Our study provides an idea to elucidate the new adsorption mechanism on Au-Li clusters and the connection between the geometries and reaction properties.

An Open-Shell Superatom Cluster Ta10- with Enhanced Stability by United d-d π Bonds and d-Orbital Superatomic States

We carried out a comprehensive study on the gas-phase reactions of Ta_n^- (n = 5-27) with nitrogen using a customized reflection time-of-flight mass spectrometer coupled with a velocity map imaging apparatus (Re-TOFMS-VMI). Among the studied tantalum clusters, Ta₁₀^- exhibits prominent mass abundance indicative of its unique inertness. DFT calculation results revealed a D_4d bipyramidal prolate structure of the most stable Ta₁₀^-, which was verified by photoelectron spectroscopy experiments. The calculations also unveiled that Ta₁₀^- has the largest HOMO-LUMO gap and second-order difference of binding energy among the studied clusters. This is associated with its well-organized superatomic orbitals, which consist of both 6s and 5d orbitals of tantalum atoms, allowing for splitting of superatomic 1D and 2P orbitals and an enlarged gap between the singly occupied molecular orbital (SOMO) and unoccupied β counterpart, which brings forth stabilization energy pertaining to Jahn-Teller distortion. Also, the SOMO exhibits a united d-d π orbital pattern that embraces the central Ta₈^- moiety.

Adsorption properties of pyramidal superatomic molecules based on the structural framework of the Au20 cluster

The pyramidal Au₂₀ cluster is a highly inert and stable superatomic molecule, but it is not suitable as a potential catalyst for covalent bond activations, e.g., CO oxidation reaction. Herein, the adsorption and electronic properties of CO molecules on various pyramidal clusters based on the structural framework of Au₂₀ are investigated using density functional theory. According to the SVB model, we constructed isoelectronic superatomic molecules with different pyramid configurations by replacing the vertex atoms of the Au₂₀ using metal M atoms (M = Li, Be, Ni, Cu, and Zn group atoms). After the CO molecules are adsorbed on the vertex atoms of these metal clusters, we analyzed the CO adsorption energies, C-O bond stretching frequencies, and electronic properties of the adsorption structures. It was found that the adsorption of CO molecules results in minimal changes in the parent geometries of the pyramidal clusters, and most adsorption structures are consistent with the geometry of CO adsorption at the vertex site of the Au₂₀ cluster. There are significant red shifts when CO molecules are adsorbed on the Ni/Pd/Pt atoms of the clusters, and their CO adsorption energies were also greater. The molecular orbitals and density of states reveal that there are overlaps between the frontier orbitals of the clusters and CO, and the electronic structure of NiAu₁₉^- is not sensitive to CO. The ETS-NOCV analysis shows that the increase in the density of the bonding area caused by the orbital interactions between the fragments is higher than the decrease in the density of the bonding area caused by Pauli repulsion, presenting that the direction of charge flow in the deformation density is from CO → clusters. From energy decomposition analysis (EDA) and NPA charge, we find a predominant covalent nature of the contributions in CO⋯M interactions (σ-donation). Our study indicates that the SVB model provides a new direction to expand the superatomic catalysts from the superatom clusters, which also provides inference for the extension of the single atom catalysis.

Structural and electronic properties for Be-doped Ptn (n = 1-12) clusters obtained by DFT calculations

In this work, we have performed a computational study on the structure and electronic properties for Be-doped Pt_n (n = 1-12) clusters in the framework of density functional theory (DFT). The most stable structures of the clusters are obtained by a structure search procedure based in simulated annealing. The results show that the Pt_nBe clusters adopt compact structure motifs with Be situated at the edge sites while only in Pt₁₁Be the Be atom occupies the center site. The energetic parameters showed that Pt₅Be, Pt₇Be and Pt₁₀Be are the most stable ones. The Pt_nBe clusters with (n = 5-7) have similar vertical ionization potential (vIP) and vertical electron affinity (vEA) parameters compared to the unary Pt clusters, while Pt₉Be and Pt₁₁Be have the higher vEA values. In particular, the d-band center is slightly higher for the doped clusters, suggesting an enhanced reactivity. The σ-holes are found more remarkable for the doped clusters, which are situated in the Be dopant and low coordinated Pt sites. The data on the infrared spectra of the clusters is also provided and showed a significant blue shift due to the vibrational modes of the Be atom. These results are useful for understanding the fundamental properties of Be-doped Pt_n clusters in the subnanometer region.