New Perspectives on the Electronic and Geometric Structure of Au70S20(PPh3)12 Cluster: Superatomic-Network Core Protected by Novel Au12(µ3-S)10 Staple Motifs

Performance of Density Functionals and Semiempirical 3c Methods for Small Gold-Thiolate Clusters

In light of the recent surge in computational studies of gold thiolate clusters, we present a comparison of popular density functionals (DFAs) and three-part corrected methods (3c-methods) on their performance by taking a data set named as AuSR18 consisting of 18 isomers of Au_n(SCH₃)_m (m ≤ n = 1-3). We have compared the efficiency and accuracy of the DFAs and 3c-methods in geometry optimization with RI-SCS-MP2 as the reference method. Similarly, the performance for accurate and efficient energy evaluation was compared with DLPNO-CCSD(T) as the reference method. The lowest energy structure among the isomers of the largest stoichiometry from our data set, AuSR18, i.e., Au₃(SCH₃)₃, is considered to evaluate the computational time for SCF and gradient evaluations. Alongside this, the numbers of optimization steps to locate the most stable minima of Au₃(SCH₃)₃ are compared to assess the efficiency of the methods. A comparison of relevant bond lengths with the reference geometries was made to estimate the accuracy in geometry optimization. Some methods, such as LC-BLYP, ωB97M-D3BJ, M06-2X, and PBEh-3c, could not locate many of the minima found by most of the other methods; thus, the versatility in locating various minima is also an important criterion in choosing a method for the given project. To determine the accuracy of the methods, we compared the relative energies of the isomers in each stoichiometry and the interaction energy of the gold core with the ligands. The dependence of basis set size and relativistic effects on energies are also compared. The following are some of the highlights. TPSS has shown accuracy, while mPWPW shows comparable speed and accuracy. For the relative energies of the clusters, the hybrid range-separated DFAs are the best option. CAM-B3LYP excels, whereas B3LYP performs poorly. Overall, LC-BLYP is a balanced performer considering both the geometry and relative stability of the structures, but it lacks diversity. The 3c-methods, although fast, are less impressive in relative stability.

Assembling Au4 Tetrahedra to 2D and 3D Superatomic Crystals Based on Superatomic-Network Model

Thiolate-protected gold nanoclusters (denoted as Au _m (SR) _n or Au _n L _m ) have received extensive attention both experimentally and theoretically. Understanding the growth mode of the Au₄ unit in Au _m (SR) _n is of great significance for experimental synthesis and the search for new gold clusters. In this work, we first build six clusters of Au₇(AuCl₂)₃, Au₁₂(AuCl₂)₄, Au₁₆(AuCl₂)₆, Au₂₂(AuCl₂)₆, and Au₃₀(AuCl₂)₆ with the Au₄ unit as the basic building blocks. Density functional theory (DFT) calculations show that these newly designed clusters have high structural and electronic stabilities. Based on chemical bonding analysis, the electronic structures of these clusters follow the superatom network (SAN) model. Inspired by the cluster structures, we further predicted an Au₄ two-dimensional (2D) monolayer and a three-dimensional (3D) crystal using graphene and diamond as templates, respectively. The computational results demonstrate that the two structures have high dynamic, thermal, and mechanical stabilities, and both structures exhibit metallic properties according to the band structures calculated at the HSE06 level. The chemical bonding analysis by the solid-state natural density partitioning (SSAdNDP) method indicates that they are superatomic crystals assembled by two electron Au₄ ^- superatoms. With this construction strategy, the new bonding pattern and properties of Au _n L _m are studied and the structure types of gold are enriched.

Structural Prediction of Anion Thiolate Protected Gold Clusters of [Au28+7n(SR)17+3n]− (n = 0-4)

Structural prediction of thiolate-protected gold nanocluster (AuNCs) with diverse charge states can enrich the understanding of this species. Till now, most expementally synthesized or theoretically predicted AuNCs structures own neutral total charge. In this work, a series of gold nanoclusters with negative total charge including [Au28(SR)17]−, [Au35(SR)20]−, [Au42(SR)23]−, [Au49(SR)26]−, and [Au56(SR)29]− are designed. Following crystallized [Au23(SR)16]- prototype structure, the inner core of the newly predicted clusters are obtained through packing crossed Au7. Next, proper protecting thiolate ligands are arranged to fullfil the duet rule to obtain Au3(2e) and Au4(2e). Extensive analysis indicates these cluster own high stabilities. Molecular orbital analysis shows that the orbitals for the populations of the valence electron locate at each Au3(2e) and Au4(2e), which demonstrates the reliability the GUM model. This work should be helpful for enriching the structural diversity of AuNCs.

A Review of State of the Art in Phosphine Ligated Gold Clusters and Application in Catalysis

Atomically precise gold clusters are highly desirable due to their well-defined structure which allows the study of structure-property relationships. In addition, they have potential in technological applications such as nanoscale catalysis. The structural, chemical, electronic, and optical properties of ligated gold clusters are strongly defined by the metal-ligand interaction and type of ligands. This critical feature renders gold-phosphine clusters unique and distinct from other ligand-protected gold clusters. The use of multidentate phosphines enables preparation of varying core sizes and exotic structures beyond regular polyhedrons. Weak gold-phosphorous (Au-P) bonding is advantageous for ligand exchange and removal for specific applications, such as catalysis, without agglomeration. The aim of this review is to provide a unified view of gold-phosphine clusters and to present an in-depth discussion on recent advances and key developments for these clusters. This review features the unique chemistry, structural, electronic, and optical properties of gold-phosphine clusters. Advanced characterization techniques, including synchrotron-based spectroscopy, have unraveled substantial effects of Au-P interaction on the composition-, structure-, and size-dependent properties. State-of-the-art theoretical calculations that reveal insights into experimental findings are also discussed. Finally, a discussion of the application of gold-phosphine clusters in catalysis is presented.

Tri- and Tetra-superatomic Molecules in Ligand-Protected Face-Fused Icosahedral (M@Au12)n (M = Au, Pt, Ir, and Os, and n = 3 and 4) Clusters

Cluster assembling has been one of the hottest topics in nanochemistry. In certain ligand-protected gold clusters, bi-icosahedral cores assembled from Au₁₃ superatoms were found to be analogues of diatomic molecules F₂, N₂, and singlet O₂, respectively, in electronic shells, depending upon the super valence bond (SVB) model. However, challenges still remain for extending the scale in cluster assembling via the SVB model. In this work, ligand-protected tri- and tetra-superatomic clusters composed of icosahedral M@Au₁₂ (M = Au, Pt, Ir, and Os) units are theoretically predicted. These clusters are stable with reasonable highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy gaps and proven to be analogues of simple triatomic (Cl₃^-, OCl₂, O₃, and CO₂) and tetra-atomic (N≡C-C≡N, and Cl-C≡C-Cl) molecules in both geometric and electronic structures. Moreover, a stable cluster-assembling gold nanowire is predicted following the same rules. This work provides effective electronic rules for cluster assembling on a larger scale and gives references for their experimental synthesis.

Metalloid gold clusters - past, current and future aspects

Gold chemistry and the synthesis of colloidal gold have always caught the attention of scientists. While Faraday was investigating the physical properties of colloidal gold in 1857 without probably knowing anything about the exact structure of the molecules, 150 years later the working group of Kornberg synthesized the first structurally characterized multi-shell metalloid gold cluster with more than 100 Au atoms, Au102(SR)44. After this ground-breaking result, many smaller and bigger metalloid gold clusters have been discovered to gain a better understanding of the formation process and the physical properties. In this review, first of all, a general overview of past investigations is given, leading to metalloid gold clusters with staple motifs in the ligand shell, highlighting structural differences in the cores of these clusters. Afterwards, the influence of the synthetic procedure on the outcome of the reactions is discussed, focusing on recent results from our group. Thereby, newly found structural motifs are taken into account and compared to the existing ones. Finally, a short outlook on possible subsequent reactions of these metalloid gold clusters is given.

Density-functional tight-binding for phosphine-stabilized nanoscale gold clusters

We report a parameterization of the second-order density-functional tight-binding (DFTB2) method for the quantum chemical simulation of phosphine-ligated nanoscale gold clusters, metalloids, and gold surfaces. Our parameterization extends the previously released DFTB2 "auorg" parameter set by connecting it to the electronic parameter of phosphorus in the "mio" parameter set. Although this connection could technically simply be accomplished by creating only the required additional Au-P repulsive potential, we found that the Au 6p and P 3d virtual atomic orbital energy levels exert a strong influence on the overall performance of the combined parameter set. Our optimized parameters are validated against density functional theory (DFT) geometries, ligand binding and cluster isomerization energies, ligand dissociation potential energy curves, and molecular orbital energies for relevant phosphine-ligated Au n clusters (n = 2-70), as well as selected experimental X-ray structures from the Cambridge Structural Database. In addition, we validate DFTB simulated far-IR spectra for several phosphine- and thiolate-ligated gold clusters against experimental and DFT spectra. The transferability of the parameter set is evaluated using DFT and DFTB potential energy surfaces resulting from the chemisorption of a PH3 molecule on the gold (111) surface. To demonstrate the potential of the DFTB method for quantum chemical simulations of metalloid gold clusters that are challenging for traditional DFT calculations, we report the predicted molecular geometry, electronic structure, ligand binding energy, and IR spectrum of Au108S24(PPh3)16.

Supramolecular Gold Chemistry: From Atomically Precise Thiolate-Protected Gold Nanoclusters to Gold-Thiolate Nanostructures

Supramolecular chemistry is defined as chemistry beyond the molecule [...].

Prediction of the Au4S crystal via a superatom network model: from clusters to solids

Prediction of the Au₄S crystal on the basis of the structural character of the Au₂₂(μ₄-S)(SH)₁₂ cluster.

Au54(Et3P)18Cl12: a structurally related cluster to Au32(Et3P)12Cl8 gives insight into the formation process

The reaction of Et3PAuCl with NaBH4 in EtOH leads to the metalloid gold cluster Au32(Et3P)12Cl8 (Au32) or Au54(Et3P)18Cl12 (Au54) depending on the work-up procedure of the reaction mixture. The molecular structure of Au54 is determined by X-ray diffraction and can be described as a fusion of two Au32 clusters showing a similar solubility. The metalloid cluster Au54 can be either described by a shell model or as a combination of tetrahedral Au4X units (X = Cl, Et3P); edge and face sharing, whereas tetrahedral Au4 units are a central motif in gold cluster chemistry. This novel Au54 gold cluster gives another unique insight into the formation or decomposition process of metalloid clusters, indicating that Au32 and Au54 form from a single yet unknown cluster source.