Photoelectron spectroscopy of binary Au cluster anions with a doped metal atom: AunM− (n=2–7), M=Pd, Ni, Zn, Cu, and Mg

Revisiting ultrasmall phosphine-stabilized rhodium-doped gold clusters AunRh (n = 5, 6, 7, 8): geometric, electronic, and vibrational properties

Incorporation of other transition metals in Au nanoclusters has been thriving recently due to its effect on their electronic and photophysical properties. Here, the ultrasmall phosphine-stabilized Rh-doped gold clusters AunRh (n = 5, 6, 7, 8), with metal core structures represented as fragments of a rhodium-centered icosahedron, are considered. The geometric and electronic properties of these nanoclusters are revisited and analyzed using density functional theory (DFT). Moreover, infrared spectra are simulated to identify the effects of Rh doping on the clusters through vibrational properties. Peaks are assigned to breathing-like normal modes for all AuRh clusters except for Au8Rh, likely due to the presence of bound Cl ligands. Unlike their pure gold core counterparts, the % motions of both Au and Rh atoms are lower in the mixed metal clusters, suggesting more restrained metal cores by rhodium, which could result in other novel physical and chemical properties not hitherto discovered.

Double σ-Aromaticity in a Planar Zinc-Doped Gold Cluster: Au9Zn. J Phys Chem A 2021;125:4606-4613. [PMID: 34014680 DOI: 10.1021/acs.jpca.1c02954]

The strong relativistic effects result in many interesting chemical and physical properties for gold and gold compounds. One of the most surprising findings has been that small gold clusters prefer planar structures. Dopants can be used to tune the electronic and structural properties of gold nanoclusters. Here we report an experimental and theoretical investigation of a Zn-doped gold cluster, Au₉Zn^-. Photoelectron spectroscopy reveals that Au₉Zn^- is a highly stable electronic system with an electron binding energy of 4.27 eV. Quantum chemical studies show that the global minimum of Au₉Zn^- has a D_3h structure with a closed-shell electron configuration (¹A₁'), which can be viewed as replacing the central Au atom by Zn in the open-shell parent Au₁₀^- cluster. The high electronic stability of Au₉Zn^- is corroborated by its extremely large HOMO-LUMO gap of 3.3 eV. Chemical bonding analyses revealed that the D_3h Au₉Zn^- are bonded by two sets of delocalized σ bonds, giving rise to double σ aromaticity and its remarkable stability. Two planar low-lying isomers are also observed, corresponding to a similar triangular structure with the Zn atom on the edge and another one with one of the corner Au atoms moved to the edge of the triangle.

Remarkable Structural Effect on the Gold-Hydrogen Analogy in Hydrogen-Doped Gold Cluster

In accordance with the well established gold-hydrogen analogy, a hydrogen atom mimics the properties of a gold atom in gold clusters. In a recent study it has been demonstrated that the properties of a hydrogen atom doped small gold cluster (Au₇H) are not in conformity with the aforementioned analogy. In this paper we study the properties of the Au₇H cluster exhaustively to re-examine the validity of the gold-hydrogen analogy in the context of adsorption of CO and O₂ molecules on pristine gold and hydrogen atom doped gold clusters. For this purpose we first determine the most stable structure of the Au₇H cluster by using an ab initio density functional theory based method with generalized gradient approximation (GGA) and Meta-GGA exchange-correlation functionals. We carry out geometry optimization by considering various planar and three-dimensional isomers of the Au₇H cluster as initial geometries. We find that the lowest energy structure of Au₇H is a planar one with C_{2 v} symmetry, and it is very close to the structure of the Au₈ cluster with D_{4 h} symmetry. Furthermore, to examine the validity of the gold-hydrogen analogy we carry out a detailed investigation of the adsorption of CO and O₂ molecules on the most stable as well as various other low energy isomers of the Au₇H cluster. We find that the adsorption energies and the extent of activation of CO and O₂ molecules on the most stable planar isomer of Au₇H are almost the same as those on the parent Au₈ cluster with D_{4 h} symmetry proving the validity of the gold-hydrogen analogy. On the other hand, for the high energy three-dimensional isomers of the Au₇H cluster obtained from the pristine Au₈ cluster with T _d symmetry, we find a significant enhancement in adsorption energy as well as the extent of activation of CO and O₂ molecules as compared to those for the corresponding pristine cluster. Therefore, the high reactivity of the 3D isomer of the Au₇H cluster may be attributed to its existence in a state which is higher in energy than its most stable planar isomer.

Probing the structures of gold-aluminum alloy clusters AuxAly(-): a joint experimental and theoretical study

Besides the size and structure, compositions can also dramatically affect the properties of alloy nanoclusters. Due to the added degrees of freedom, determination of the global minimum structures for multi-component nanoclusters poses even greater challenges, both experimentally and theoretically. Here we report a systematic and joint experimental/theoretical study of a series of gold-aluminum alloy clusters, AuxAly(-) (x + y = 7,8), with various compositions (x = 1-3; y = 4-7). Well-resolved photoelectron spectra have been obtained for these clusters at different photon energies. Basin-hopping global searches, coupled with density functional theory calculations, are used to identify low-lying structures of the bimetallic clusters. By comparing computed electronic densities of states of the low-lying isomers with the experimental photoelectron spectra, the global minima are determined. It is found that for y ≥ 6 there is a strong tendency to form the magic-number square bi-pyramid motif of Al6(-) in the AuxAly(-) clusters, suggesting that the Al-Al interaction dominates the Au-Au interaction in the mixed clusters. A closely related trend is that for x > 1, the gold atoms tend to be separated by Al atoms unless only the magic-number Al6(-) square bi-pyramid motif is present, suggesting that in the small-sized mixed clusters, Al and Au components do not completely mix with one another. Overall, the Al component appears to play a more dominant role due to the high robustness of the magic-number Al6(-) square bi-pyramid motif, whereas the Au component tends to be either "adsorbed" onto the Al6(-) square bi-pyramid motif if y ≥ 6, or stays away from one another if x < y < 6.

Dopant induced modulation in the structure and electronic properties of Au10 cluster

DFT calculations at PBE0/SDD ∪ 6-31++G(d,p) level suggest that doped Au₁₀ clusters (with alkali and alkaline earth metals as dopants) are better potential candidates for use in heterogeneous catalysis.

Density functional study on the structural, electronic, and magnetic properties of 3d transition-metal-doped Au5 clusters

Density functional calculations have been performed for the structural, electronic, and magnetic properties of Au5M (M = Sc-Zn) clusters. Geometry optimizations indicate that the M atoms in low-energy Au5M isomers prefer to occupy the most highly coordinated position. The ground-state clusters except Au5Sc possess a planar structure. The vibrational spectra of the doped clusters are completely different from that of a pure gold cluster. The relative stability and chemical activity are investigated through the averaged binding energy and energy gap for the most stable Au5M clusters. It is found that the impurity atoms (not including the Zn atom) can enhance the thermal stability of the host cluster. The chemical activity of Au5M clusters is higher than that of the Au6 cluster. The calculated energy gaps are in accord with available approximate experimental data. The vertical ionization potential, the electron affinity, and photoelectron spectrum are computed and simulated theoretically for all of the ground-state clusters. The magnetism analyses show that the magnetic moment of these Au5M clusters varies from 0 to 5 μB by substituting a Au atom in a Au6 cluster with various M atoms and is mainly localized on the M atom for M = Ti-Ni.

The PtAl(-) and PtAl2(-) anions: theoretical and photoelectron spectroscopic characterization

We report a joint photoelectron spectroscopic and theoretical study of the PtAl(-) and PtAl2(-) anions. The ground state structures and electronic configurations of these species were identified to be C∞v, (1)Σ(+) for PtAl(-), and C2v, (2)B1 for PtAl2(-). Structured anion photoelectron spectra of these clusters were recorded and interpreted using ab initio calculations. Good agreement between theory and experiment was found. All experimental features were successfully assigned to one-electron transitions from the ground state of the anions to the ground or excited states of the corresponding neutral species.

A DFT study on structure, stabilities and electronic properties of double magnesium doped gold clusters

The doping of two Mg atoms on Au-clusters has considerable effects on the structure and stability of gold clusters. The doped clusters enhance the stability of pure Au-clusters as observed from the binding energy plot.