Correlation between electronic properties and reactivity toward oxygen of tetrahedral gold–silver clusters

From 8- to 18-Cluster Electrons Superatoms: Evaluation via DFT Calculations of the Ligand-Protected W@Au12(dppm)6 Cluster Displaying Distinctive Electronic and Optical Properties

The iconic W@Au₁₂ icosahedral bare cluster reaches the favorable closed-shell superatomic electron configuration 1S² 1P⁶ 1D¹⁰, making it an 18-cluster electron (18-ce) superatom. Here, we pursue the evaluation of a ligand-protected counterpart based on the construction of a fully phosphine-protected [W@Au₁₂(dppm)₆] cluster strongly related to the characterized [Au₁₃(dppm)₆]⁵⁺ homometallic counterpart. The later cluster has the same total number of valence electrons as the former but is considered an 8-ce superatom with 1S² 1P⁶ configuration. The fundamental differences between 8- and 18-ce species are investigated. The character of the frontier orbitals varies from 1P/1D in the 8-ce case to a 1D/ligand for 18-ce species, enabling an efficient charge transfer toward the ligands upon irradiation, being interesting for electron injection in optoelectronic devices and black absorbers applications. Excited-state properties are also revisited, showing different geometrical and electronic structure variations between 8- and 18-ce species. Moreover, the continuum between the 8- and 18-ce limits has been explored by varying the nature of the encapsulated dopant between group 6 and group 11. The transition between the 8- and 18-ce counts can be formally situated between Pt (8-ce) and Ir (18-ce). Thus, 18-ce derivatives obtained as doped counterparts of homometallic gold clusters can introduce useful alternatives to achieve different properties in related structural motifs, which can be further explored owing to their extension of the well-established versatility of current gold nanoclusters.

Triple 1D[triple bond, length as m-dash]1D superatomic bonding. Au22(dppo)6 as a Π4- and Δ2-triply bonded cluster based on Au11 assembled units

δ-Bonds have been intimately related to metal-metal bonds of d-elements since the archetypal d⁴-d⁴ [Re₂Cl₈]^2- ion with a σ²π⁴δ² bond. Currently, the notion of multiple superatom arrangements as initial steps toward molecular materials within the building-up approach is dominated by P-shell characteristics, as given in the well-described Au₂₅(SR)₁₈ ligand protected cluster. In this work we rationalize the Au₂₂(dppo)₆ cluster as a triple-bonded 22-valence electron (ve) supermolecule, featuring a bonding scheme based on 1D + 1D shell combinations, which largely contrasts with the 14-ve Au₃₈(SR)₂₄ with mainly 1P + 1P patterns mimicking a F₂ molecule. The resulting Π⁴Δ²-bonding pattern shows an unprecedented superatomic counterpart of a d-shell based bond inherently related to transition-metal dimers, adding useful key aspects to the understanding of species based on cluster-assembly.

Theoretical Studies on the Direct Propylene Epoxidation Using Gold-Based Catalysts: A Mini-Review

Direct propylene epoxidation using Au-based catalysts is an important gas-phase reaction and is clearly a promising route for the future industrial production of propylene oxide (PO). For instance, gold nanoparticles or clusters that consist of a small number of atoms demonstrate unique and even unexpected properties, since the high ratio of surface to bulk atoms can provide new reaction pathways with lower activation barriers. Support materials can have a remarkable effect on Au nanoparticles or clusters due to charge transfer. Moreover, Au (or Au-based alloy, such as Au–Pd) can be loaded on supports to form active interfacial sites (or multiple interfaces). Model studies are needed to help probe the underlying mechanistic aspects and identify key factors controlling the activity and selectivity. The current theoretical/computational progress on this system is reviewed with respect to the molecular- and catalyst-level aspects (e.g., first-principles calculations and kinetic modeling) of propylene epoxidation over Au-based catalysts. This includes an analysis of H2 and O2 adsorption, H2O2 (OOH) species formation, epoxidation of propylene into PO, as well as possible byproduct formation. These studies have provided a better understanding of the nature of the active centers and the dominant reaction mechanisms, and thus, could potentially be used to design novel catalysts with improved efficiency.

Au19M (M=Cr, Mn, and Fe) as magnetic copies of the golden pyramid

An investigation on structure, stability, and magnetic properties of singly doped Au19M (M=Cr, Mn, and Fe) clusters is carried out by means of density functional theory calculations. The studied clusters prefer forming magnetic versions of the unique tetrahedral Au20. Stable sextet Au19Cr is identified as the least reactive species and can be qualified as a magnetic superatom. Analysis on cluster electronic structures shows that the competition between localized and delocalized electronic states governs the stability and magnetic properties of Au19M clusters.

Doping the cage. Re@Au11Pt and Ta@Au11Hg, as novel 18-ve trimetallic superatoms displaying a doped icosahedral golden cage

Trimetallic superatomic clusters. Theoretical proposal and evaluation of the 18-ve Ta@Au₁₁Hg and Re@Au₁₁Pt clusters.

Spin and structural features of oxygen dissociation on tetrahedral Ag20 and Ag19Au clusters

The spin-crossing mechanism of oxygen dissociation on Ag₂₀ and monodoped Ag₁₉Au clusters was investigated using spin-polarized scalar-relativistic DFT. The activation energy decreases by 11–29 kJ mol⁻¹ relative to that for the spin-conserving pathway.