On the variation of cluster core characteristics by an endohedral atom. Shape variation in 8-ce [EAu4(PPh3)4]2+ (E = N, P, As, Sb) clusters

Atomically precise gold superatoms have attracted interest owing to their suitable use as building blocks for cluster-assembled materials, favoring ordered structures with advanced properties. In this sense, expanding their versatility is a relevant issue for controlling their properties and retaining a specific nuclearity. Interestingly, the reported structure for isoelectronic [Au4N(PPh3)4]+ and [Au4Sb(PPh3)4]+ clusters denotes two contrasting shapes featuring a tetrahedral and square pyramidal structure, respectively. Herein, we further explore the [Au4E(PPh3)4]+ (E = N, P, As, Sb) series in order to evaluate energetic and structural factors determining the overall shape. Our results show a favorable [Au4(PPh3)4]4+/E3- interaction energy, predicting particular patterns in their UV-vis spectrum. Thus, the use of dopant atoms is enabled to vary the core shape and, in turn, to modify the cluster properties, which serve as a structural control, in addition to ligand-based and size approaches.

On the halide aggregation into the [Au4(PPh3)4]4+ cluster core. Insights from structural, optical and interaction energy analysis in [(Ph3PAu)4X2]2+ and [(Ph3PAu)4X]3+ species (X = Cl-, Br-, I-)

The aggregation of halide atoms into gold clusters offers an interesting scenario for the development of novel metal-based cavities for anion recognition and sensing applications. Thus, further understanding of the different contributing terms leading to efficient cluster-halide aggregation is relevant to guide their synthetic design. In this report, we evaluate the formation of [(Ph3PAu)4X2]2+ and [(Ph3PAu)4X]3+ species (X = Cl-, Br-, I-) in terms of different energy contributions underlying the stabilization of the cluster-halide interaction, and the expected UV-vis absorption profiles as a result of the variation in frontier orbital arrangements. Our results denote that a non-planar Au4 core shape enables enhanced halide aggregation, which is similar for Cl-, Br-, and I-, in comparison to the hypothetical planar Au4 counterparts. The electrostatic nature of the interaction involves a decreasing ion-dipole term along with the series, and for iodine species, higher-order electrostatic contributions become more relevant. Hence, the obtained results help in gaining further understanding of the different stabilizing and destabilizing contributions to suitable cluster-based cavities for the incorporation of different monoatomic anions.

Manifestation of the interplay between spin-orbit and Jahn-Teller effects in Au25 superatom UV-Vis fingerprint spectra

Atomically precise nanoclusters play an important role in nanoscale catalysis, photonics, and quantum information science. Their nanochemical properties arise from their unique superatomic electronic structures. As the flagship of atomically precise nanochemistry, the Au₂₅(SR)₁₈ nanocluster exhibits tunable spectroscopic signatures that are sensitive to the oxidation state. This work aims to unravel the physical underpinnings of the spectral progression of Au₂₅(SR)₁₈ nanocluster using variational relativistic time-dependent density functional theory. The investigation will focus on the effects of superatomic spin-orbit coupling, its interplay with Jahn-Teller distortion, and their manifestations in the absorption spectra of Au₂₅(SR)₁₈ nanoclusters of different oxidation states.

Self-isomerization of nearly planar superatoms formed by actinide embedded gold clusters

First-principles calculations show a self-isomerization process of the nearly planar superatom, in which the maximum energy difference between different extreme points is below 0.1 eV and a crossing between singlet and triplet states is also involved. Further UV-Vis spectra reveal a correlation between the spectra and structures caused by self-isomerization.

N-Heterocyclic carbene derivatives to modify gold superatom characteristics. Tailorable electronic and optical properties of [Au11(PPh3)7LCl2]+ as a cluster from relativistic DFT

Atomically precise gold superatoms are useful building blocks whose properties can be tuned by the proper choice of ligands in the protecting ligand layer. Herein, different N-heterocyclic carbene (NHC) derivatives of the prototypical [Au₁₁(PPh₃)₈Cl₂]⁺ cluster were evaluated by the replacement of a single ligand, which led to isoelectronic [Au₁₁(PPh₃)₇(NHC)Cl₂]⁺ species, enabling further understanding of the possible changes in the resulting cluster properties. Our results reveal the great variation in the HOMO-LUMO gap and optical features when going from strong to weak σ-donor NHC ligands. The Au₁₁ core retains similar features throughout the series, and the lowest unoccupied orbital (LUMO) is further stabilized, indicating greater π*-NHC character for the weaker σ-donor ligands, which favors directional core-ligand optical charge transfer to a single ligand. The ligand-tailored behavior of the [Au₁₁(PPh₃)₇LCl₂]⁺ cluster underlies its tunable characteristics, indicating its potential use in novel devices as building blocks of nanostructured materials, which favors further versatility and applications of superatomic clusters.

Insight Into the Stability and Electronic and Optical Properties of N-Heterocyclic Carbene Analogues of Halogen/Phosphine-Protected Au13 Superatomic Clusters

Atomically precise gold nanoclusters (AuNCs) belong to a relevant area offering useful templates with tunable properties toward functional nanostructures. In this work, we explored the feasible incorporation of N-heterocyclic carbenes (NHCs), as part of the protecting-ligand shell in AuNCs. Our results, which are based on the substitution of phosphine ligands in experimentally characterized AuNCs by NHCs in various eight-electron superatoms Au₁₃ and M₄Au₉ (M = Cu, Ag), indicate similar electronic structure and stability but somewhat different optical properties. These findings support the feasible obtention of novel targets for explorative synthetic efforts featuring NHC ligands on medium-sized species based on the recurrent Au₁₃ icosahedral core. The hypothetical species appear to be interesting templates for building blocks in nanostructured materials with tuned properties, which encourage experimental exploration of ligand versatility in homo- and heterometallic superatomic clusters.

Ligand-Core Interaction in Ligand-Protected Ag25(XR)18 (X= S, Se, Te) Superatoms. Evaluation of Anchor Atom Role via Relativistic DFT Calculations

The isostructural and isoelectronic silver [Ag25(SR)18]- (R=Ligand) cluster to [Au25(SR)18]- gold clusters allows to further understand the fundamental similarities between Au and Ag, at the ultrasmall nanoscale (< 2 nm)...

Superatomic Rydberg State Excitation

Superatomic molecular orbitals (SAMOs) have symmetries (angular quantum numbers) similar to those of atoms, and thus, it is possible to realize Rydberg state excitations (RSEs) in superatomic molecules. In this Letter, the feasibility of superatomic Rydberg state excitation (SRSE) is explored using gold superatoms based on first-principles calculations. The results show that the SRSE exists in the high and low excited states of the gold superatoms and their SAMOs make a major contribution to electronic transitions. The radial distribution function of electronic density shows that the main distribution of electrons in the lowest unoccupied molecular orbitals and other unoccupied superatomic molecular orbitals is extremely far from the geometric center, and thus, they can be unambiguously identified as Rydberg orbitals. We found that due to the two-dimensional ductility of the planar SAMOs, superatoms are superior in the RSE regulation. Our findings may provide a new source of superatom-based RSE and will contribute to the regulation and efficient preparation of Rydberg states.

Evaluation of ultrasmall coinage metal M13(dppe)6 M = Cu, Ag, and Au clusters. Bonding, structural and optical properties from relativistic DFT calculations

Ultrasmall ligand-protected clusters are prototypical species for evaluating the variation at the bottom of the nanoscale range. Here we explored the ultrasmall gold-phosphine M₁₃(dppe)₆ cluster, as a prototypical framework to gain insights into the fundamental similarities and differences between Au, Ag, and Cu, in the 1-3 nm size range, via relativistic DFT calculations. Different charge states involving 8- and 10-cluster electron (ce) species with a 1S²1P⁶ and 1S²1P⁶1D² configuration, leading to structural modification in the Au species between Au₁₃(dppm)₆⁵⁺ and Au₁₃(dppm)₆³⁺, respectively. Furthermore, this structural distortion of the M₁₃ core is found to occur to a lower degree for the calculated Ag and Cu counterparts. Interestingly, optical properties exhibit similar main patterns along with the series, inducing a blue-shift for silver and copper, in comparison to the gold parent cluster. For 10-ce species, the main features of 8-ce are retained with the appearance of several weak transitions in the range. The ligand-core interaction is enhanced for gold counterparts and decreased for lighter counterparts resulting in the Au > Cu > Ag trend for the interaction stabilization. Hence, the Ag and Cu counterparts of the Au₁₃(dppm)₆ cluster appear as useful alternatives, which can be further explored towards different cluster alternatives for building blocks for nanostructured materials.

Toward the Formation of N-Heterocyclic-Carbene-Protected Gold Clusters of Various Nuclearities. A Comparison with Their Phosphine-Protected Analogues from Density Functional Theory Calculations

The structure and bonding of a series of selected phosphine-protected gold clusters (Au_n-P) of nuclearity varying from n = 6 to 13 were investigated by density functional theory (DFT) calculations and compared to those of the hypothetical homologues in which phosphines were replaced by N-heterocyclic carbene (NHC) analogues (Au_n-C). Both the Au_n-P and Au_n-C series exhibit similar stabilities and structural features, except for n = 6, where some differences are noted. The NHC ligands are found to be even slightly more strongly bonded to the gold core (by a few kilocalories per mole per ligand) than phosphines. Investigation of the optical properties of both series using time-dependent DFT calculations indicates similarities in the nature and energies of the UV-vis optical transitions and, consequently, relatively similar shapes of the simulated spectra, with a general blue-shift tendency when going from Au_n-P to Au_n-C. The fluorescence behavior observed experimentally for some of the Au_n-P species is expected to occur also for their Au_n-C analogues, which can be extended to other carbene-ligand-protected nanoclusters. Our results show that it should be possible to stabilize gold clusters with NHC ligands, in relation to the seminal Au₁₃-ligand-protected core, offering novel building blocks for the design of nanostructured materials with various properties.

Electron counting and bonding patterns in assemblies of three and more silver-rich superatoms

DFT calculations were carried out on a series of cluster cores, the framework of which was made of the condensation of several Pt@Ag12-centered icosahedra. Icosahedral condensations through vertex-sharing, face-sharing, and interpenetration were considered and their favored electron counts were determined from their stable closed-shell configurations. A large number of the computed assemblies of n icosahedral superatomic units can be considered as isolobal analogs of stable, closed-shell n-atom molecules, most of them obeying the octet rule. The larger the degree of fusion between icosahedra, the stronger the interaction between them. For example, it was possible to design 3-icosahedral supermolecular cores analogous to CO2, SF2, or [I3]-, but also to the not-yet-isolated cyclic O3. Supermolecules equivalent to non-stable molecules can also be designed. Indeed, differences exist between atoms and superatoms, and original icosahedra assemblies with no "molecular" analogs are also likely to exist, especially with compact structures and/or systems made of a large number of fused superatoms.

Electron count and electronic structure of bare icosahedral Au32and Au33ionic nanoclusters and ligated derivatives. Stable models with intermediate superatomic shell fillings

The Au₃₂icosahedral cage can adapt its shape to several electron counts.

Potential of N-heterocyclic carbene derivatives from Au13(dppe)5Cl2gold superatoms. Evaluation of electronic, optical and chiroptical properties from relativistic DFT

N-heterocyclic carbene (NHC) introduction into well-defined atomically precise gold superatoms allows efficient control of structural, optical, chiroptical and emission features of the Au₁₃Cl₂core, related to the classical chiral [Au₁₃Cl₂(dppe)₅]³⁺nanocluster.

Structurally Precise Dichalcogenolate-Protected Copper and Silver Superatomic Nanoclusters and Their Alloys

The chalcogenolato silver and copper superatoms are currently a topic of cutting edge research besides the extensively studied Au _n(SR) _m clusters. Crystal structure analysis is an indispensable tool to gain deep insights into the anatomy of these sub-nanometer clusters. The metal framework and spatial arrangement of the chalcogenolates around the metal core assist in unravelling the structure-property relationships and fundamental mechanisms involved in their fabrication. In this Account, we discuss our contribution toward the development of dichalcogenolato Ag and Cu cluster chemistry covering their fabrication and precise molecular structures. Briefly introducing the significance of the single crystal structures of the atomically precise clusters, the novel dichalcogenolated two-electron superatomic copper and its alloy systems are presented first. The [Cu₁₃{S₂CNR}₆{C≡CR'}₄]⁺ is so far the first unique copper cluster having Cu₁₃ centered cuboctahedra, which is a miniature of bulk fcc structure. The galvanic exchange of the central Cu with Ag or Au results in a similar anatomy of formed bimetallic [Au/Ag@Cu₁₂(S₂CN ⁿBu₂)₆(C≡CPh)₄][CuCl₂] species. This is unique in the sense that other contemporary M₁₃ cores in group 11 superatomic chemistry are compact icosahedra. The central doping of Ag or Au significantly affects the physiochemical properties of the bimetallic Cu-rich clusters. It is manifested in the dramatic quantum yield enhancement of the doped species [Au@Cu₁₂(S₂CN ⁿBu₂)₆(C≡CPh)₄]⁺ with a value of 0.59 at 77 K in 2-MeTHF. In the second part, the novel eight-electron dithiophosphate- and diselenophosphate-protected silver systems are presented. A completely different type of architecture was revealed for the first time from the successful structural determination of [Ag₂₁{S₂P(O ⁱPr)₂}₁₂]⁺, [Ag₂₀{S₂P(O ⁱPr)₂}₁₂] and [Au@Ag₁₉{S₂P(OPr)₂}₁₂]. They exhibit a nonhollow M₁₃ (Ag or AuAg₁₂) icosahedron, capped by 8 and 7 Ag atoms in the former and latter two species, respectively. The overall metal core units are protected by 12 dithiophosphate ligands and the metal-ligand interface structure was found to be quite different from that of Au _n(SR) _m. Notably, the [Ag₂₀{S₂P(O ⁱPr)}₁₂] cluster provides the first structural evidence of a silver superatom with a chiral metallic core. This chirality arises through the simple removal of one of capping Ag⁺ cations of [Ag₂₁{S₂P(O ⁱPr)₂}₁₂]⁺ present on its C₃ axis. Further, the effects of the ligand exchange on the structures of [Ag₂₀{Se₂P(O ⁱPr)₂}₁₂], [Ag₂₁{Se₂P(OEt)₂}₁₂]⁺, and [AuAg₂₀{Se₂P(OEt)₂}₁₂]⁺ are studied extensively. The structure of the former species is similar to its dithiophosphate counterpart ( C₃ symmetry). The latter two ( T symmetry) differ in the arrangement of 8 capping Ag atoms, as they form a cube engraving the Ag₁₃ (AuAg₁₂) icosahedron. The blue shifts in absorption spectra and photoluminescence further indicate the strong influence of the central Au atom in the doped clusters. Finally, the first paradigm of unusual heteroatom doping induced size-structure transformations is discussed by presenting the case of formation of [Au₃Ag₁₈{Se₂P(O ⁱPr)₂}₁₂]⁺ upon Au doping into [Ag₂₀{Se₂P(O ⁱPr)₂}₁₂]⁰. Finally, before concluding this Account, we discuss the possibility of many unique structural isomers with different physical properties for the aforementioned Ag superatoms which need to be explored extensively in the future.

[Au12 (SR)6 ]2- , As Smaller 8-Electron Gold Nanocluster Retaining an SP3 -Core. Evaluation of Bonding and Optical Properties from Relativistic DFT Calculations

Exploring the versatility of atomically precise clusters is a relevant issue in the design of functional nanostructures. Superatomic clusters offer an ideal framework to gain further understanding of the different distinctive size-dependent physical and chemical properties. Here, we propose [Au12 (SR)6 ]2- as a minimal 8-electron superatom related to the prototypical [Au25 (SR)18 ]- cluster, depicting half of its core-mass (2.3 kDa vs 5.0 kDa). The [Au12 (SMe)6 ]2- cluster fulfills a 1S2 1P6 electronic configuration, with a distorted tetrahedral Au8 core further viewed as an SP3 -hybridized superatom. The distinctive optical properties show a blue-shift for the first relevant 1P→1D transition, in comparison to [Au25 (SR)18 ]- . In addition, chiroptical activity is observed, denoting intrinsic core chirality. We expect that our results can shed light into the variation of the molecular properties according to the size-dependent properties, and serve as guidelines for further experimental exploration of minimal or ultrasmall nanoclusters.