Au108S24(PPh3)16: A Highly Symmetric Nanoscale Gold Cluster Confirms the General Concept of Metalloid Clusters

The reduction of (Ph₃P)AuCl with NaBH₄ in the presence of HSC(SiMe₃)₃, leads to one of the largest metalloid gold clusters: Au₁₀₈S₂₄(PPh₃)₁₆ ( 1 ). Within 1 an octahedral Au₄₄ core of gold atoms arranged as in Au metal is surrounded by 48 oxidized Au atoms of an Au₄₈S₂₄ shell, a novel building block in gold chemistry. The protecting Au₄₈S₂₄ shell is completed by additional 16 Au(PPh₃) units, leading to a complete protection of the gold core. Within 1 the Au–Au distances get more molecular on going from the center to the ligand shell. Cluster 1 represents novel structural motives in the field of metalloid gold clusters which also are partly typical for metal atoms in metalloid clusters: M_n R_m (n >m ).     

Bare Clusters Derived from Protein Templates: Au25+, Au38+ and Au102+

A discrete sequence of bare gold clusters of well‐defined nuclearity, namely Au₂₅⁺, Au₃₈⁺ and Au₁₀₂⁺, formed in a process that starts from gold‐bound adducts of the protein lysozyme, were detected in the gas phase. It is proposed that subsequent to laser desorption ionization, gold clusters form in the gas phase, with the protein serving as a confining growth environment that provides an effective reservoir for dissipation of the cluster aggregation and stabilization energy. First‐principles calculations reveal that the growing gold clusters can be electronically stabilized in the protein environment, achieving electronic closed‐shell structures as a result of bonding interactions with the protein. Calculations for a cluster with 38 gold atoms reveal that gold interaction with the protein results in breaking of the disulfide bonds of the cystine units, and that the binding of the cysteine residues to the cluster depletes the number of delocalized electrons in the cluster, resulting in opening of a super‐atom electronic gap. This shell‐closure stabilization mechanism confers enhanced stability to the gold clusters. Once formed as stable magic number aggregates in the protein growth medium, the gold clusters become detached from the protein template and are observed as bare Au_n⁺ (n=25, 38, and 102) clusters.     

Local Geometric Effects on Stability and Energy Gap of Thiolate‐Protected Gold Nanoparticles

Thiolate‐protected gold nanoclusters, Au_m(SR)_n, have potential applications in many fields due to their high stability and remarkable electronic properties. However, the controlling factors in determining the stability and HOMO–LUMO gap of Au_m(SR)_n remain controversial, despite decades of work on the topic. Through DFT calculations, including nonlocal many‐body dispersion (MBD) interactions, the geometric and electronic properties of Au_m(SR)_n clusters are investigated. Calculations demonstrate that the MBD interactions are essential for correctly describing the geometry and energy of the clusters. Greater anisotropic polarization and more atoms distributed in the shell of the clusters lead to more pronounced MBD interactions and higher stability of the clusters. Furthermore, the HOMO–LUMO gap of the clusters strongly depends on the gold core. These results provide critical clues for understanding and designing Au_m(SR)_n clusters.     

Observable Structures of Small Neutral and Anionic Gold Clusters

Since gold clusters have mostly been studied theoretically by using DFT calculations, more accurate studies are of importance. Thus, small neutral and anionic gold clusters (Au_n and Au_n^?, n=4–7) were investigated by means of coupled cluster with singles, doubles, and perturbative triple excitations [CCSD(T)] calculations with large basis sets, and some differences between DFT and CCSD(T) results are discussed. Interesting isomeric structures that have dangling atoms were obtained. Structures having dangling atoms appear to be stable up to n=4 for neutral gold clusters and up to n=7 for anionic clusters. The relative stabilities and electronic properties of some isomers and major structures are discussed on the basis of the CCSD(T) calculations. This accurate structure prediction of small gold clusters corresponding to experimental photoelectron spectral peaks is valuable in the field of atom‐scale materials science including nanocatalysts.     

Laser ablation synthesis of new gold phosphides using red phosphorus and nanogold as precursors. Laser desorption ionisation time‐of‐flight mass spectrometry

Gold phosphides show unique optical or semiconductor properties and there are extensive high technology applications, e.g. in laser diodes, etc. In spite of the various AuP structures known, the search for new materials is wide. Laser ablation synthesis is a promising screening and synthetic method. Generation of gold phosphides via laser ablation of red phosphorus and nanogold mixtures was studied using laser desorption ionisation time‐of‐flight mass spectrometry (LDI TOFMS). Gold clusters Au_m⁺ (m = 1 to ~35) were observed with a difference of one gold atom and their intensities were in decreasing order with respect to m. For P_n⁺ (n = 2 to ~111) clusters, the intensities of odd‐numbered phosphorus clusters are much higher than those for even‐numbered phosphorus clusters. During ablation of P‐nanogold mixtures, clusters Au_m⁺ (m = 1‐12), P_n⁺ (n = 2‐7, 9, 11, 13–33, 35–95 (odd numbers)), AuP_n⁺ (n = 1, 2–88 (even numbers)), Au₂P_n⁺ (n = 1‐7, 14–16, 21–51 (odd numbers)), Au₃P_n⁺ (n = 1‐6, 8, 9, 14), Au₄P_n⁺ (n = 1‐9, 14–16), Au₅P_n⁺ (n = 1‐6, 14, 16), Au₆P_n⁺ (n = 1‐6), Au₇P_n⁺ (n = 1‐7), Au₈P_n⁺ (n = 1‐6, 8), Au₉P_n⁺ (n = 1‐10), Au₁₀P_n⁺ (n = 1‐8, 15), Au₁₁P_n⁺ (n = 1‐6), and Au₁₂P_n⁺ (n = 1, 2, 4) were detected in positive ion mode. In negative ion mode, Au_m^– (m = 1–5), P_n^– (n = 2, 3, 5–11, 13–19, 21–35, 39, 41, 47, 49, 55 (odd numbers)), AuP_n^– (n = 4–6, 8–26, 30–36 (even numbers), 48), Au₂P_n^– (n = 2–5, 8, 11, 13, 15, 17), Au₃P_n^– (n = 6–11, 32), Au₄P_n^– (n = 1, 2, 4, 6, 10), Au₆P₅^–, and Au₇P₈^– clusters were observed. In both modes, phosphorus‐rich Au_mP_n clusters prevailed. The first experimental evidence for formation of AuP₆₀ and gold‐covered phosphorus Au₁₂P_n (n = 1, 2, 4) clusters is given. The new gold phosphides generated might inspire synthesis of new Au‐P materials with specific properties. Copyright © 2012 John Wiley & Sons, Ltd.     

Controllable Conversion of CO2 on Non‐Metallic Gold Clusters

Gold nanoparticles in metallic or plasmonic state have been widely used to catalyze homogeneous and heterogeneous reactions. However, the catalytic behavior of gold catalysts in non‐metallic or excitonic state remain elusive. Atomically precise Au_n clusters (n=number of gold atoms) bridge the gap between non‐metallic and metallic catalysts and offer new opportunities for unveiling the hidden properties of gold catalysts in the metallic, transition regime, and non‐metallic states. Here, we report the controllable conversion of CO₂ over three non‐metallic Au_n clusters, including Au₉, Au₁₁, and Au₃₆, towards different target products: methane produced on Au₉, ethanol on Au₁₁, and formic acid on Au₃₆. Structural information encoded in the non‐metallic clusters permits a precise correlation of atomic structure with catalytic properties and hence, provides molecular‐level insight into distinct reaction channels of CO₂ hydrogenation over the three non‐metallic Au catalysts.     

Density functional study of structural and electronic properties of maximum‐spin n+1Aun−1Ag clusters

The structures and relative stabilities of high‐spin ⁿ⁺¹Au_n?1Ag and ⁿAu_n?1Ag⁺ (n = 2–8) clusters have been studied with density functional calculation. We predicted the existence of a number of previously unknown isomers. Our results revealed that all structures of high‐spin neutral or cationic Au_n?1Ag clusters can be understood as a substitution of an Au atom by an Ag atom in the high‐spin neutral or cationic Au_n clusters. The properties of mixed gold–silver clusters are strongly sized and structural dependence. The high‐spin bimetallic clusters tend to be holding three‐dimensional geometry rather than planar form represented in their low‐spin situations. Silver atom prefers to occupy those peripheral positions until to n = 8 for high‐spin clusters, which is different from its position occupied by light atom in the low‐spin situations. Our theoretical calculations indicated that in various high‐spin Au_n?1Ag neutral and cationic species, ⁵Au₃Ag, ³AuAg and ⁵Au₄Ag⁺ hold high stability, which can be explained by valence bond theory. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Ligand‐Stabilized and Atomically Precise Gold Nanocluster Catalysis: A Case Study for Correlating Fundamental Electronic Properties with Catalysis

We present results from our investigations into correlating the styrene‐oxidation catalysis of atomically precise mixed‐ligand biicosahedral‐structure [Au₂₅(PPh₃)₁₀(SC₁₂H₂₅)₅Cl₂]²⁺ (Au₂₅‐bi) and thiol‐stabilized icosahedral core–shell‐structure [Au₂₅(SCH₂CH₂Ph)₁₈]^? (Au₂₅‐i) clusters with their electronic and atomic structure by using a combination of synchrotron radiation‐based X‐ray absorption fine‐structure spectroscopy (XAFS) and ultraviolet photoemission spectroscopy (UPS). Compared to bulk Au, XAFS revealed low Au–Au coordination, Au? Au bond contraction and higher d‐band vacancies in both the ligand‐stabilized Au clusters. The ligands were found not only to act as colloidal stabilizers, but also as d‐band electron acceptor for Au atoms. Au₂₅‐bi clusters have a higher first‐shell Au coordination number than Au₂₅‐i, whereas Au₂₅‐bi and Au₂₅‐i clusters have the same number of Au atoms. The UPS revealed a trend of narrower d‐band width, with apparent d‐band spin–orbit splitting and higher binding energy of d‐band center position for Au₂₅‐bi and Au₂₅‐i. We propose that the differences in their d‐band unoccupied state population are likely to be responsible for differences in their catalytic activity and selectivity. The findings reported herein help to understand the catalysis of atomically precise ligand‐stabilized metal clusters by correlating their atomic or electronic properties with catalytic activity.     

Molecular orbital analysis of the bonding in high nuclearity gold cluster compounds

Extended Hückel molecular orbital calculations on high nuclearity gold clusters of the general type [Au(AuPH₃)_n]^x+ have demonstrated that they can be classified into two broad topological classes according to the three-dimensional disposition of the peripheral gold atoms. If they lie approximately on a sphere they are characterised by a total of 12n + 18 valence electrons, but if they adopt a toroidal or eliptical arrangement the total electron count is 12n + 16. The computed energy differences between alternative polyhedral geometries is generally small and accounts for the stereochemical non-rigidity of the gold cluster compounds in solution. Detailed aspects of the structures of the high nuclearity gold cluster compounds have been interpreted in terms of molecular orbital calculations on clusters derived from the centred chair [Au₇(PH₃)₆]⁺ by edge- and face-capping with Au(PH₃)⁺ fragments.     

Far‐Infrared Spectra of Yttrium‐Doped Gold Clusters AunY (n=1–9)

The geometric, spectroscopic, and electronic properties of neutral yttrium‐doped gold clusters Au_nY (n=1–9) are studied by far‐infrared multiple photon dissociation (FIR‐MPD) spectroscopy and quantum chemical calculations. Comparison of the observed and calculated vibrational spectra allows the structures of the isomers present in the molecular beam to be determined. Most of the isomers for which the IR spectra agree best with experiment are calculated to be the energetically most stable ones. Attachment of xenon to the Au_nY cluster can cause changes in the IR spectra, which involve band shifts and band splittings. In some cases symmetry changes, as a result of the attachment of xenon atoms, were also observed. All the Au_nY clusters considered prefer a low spin state. In contrast to pure gold clusters, which exhibit exclusively planar lowest‐energy structures for small sizes, several of the studied species are three‐dimensional. This is particularly the case for Au₄Y and Au₉Y, while for some other sizes (n=5, 8) the 3D structures have an energy similar to that of their 2D counterparts. Several of the lowest‐energy structures are quasi‐2D, that is, slightly distorted from planar shapes. For all the studied species the Y atom prefers high coordination, which is different from other metal dopants in gold clusters.     

Activation and Transformation of Ethane by Au2VO3+ Clusters with Closed‐Shell Electronic Structures

The study of chemical reactions between gold‐containing heteronuclear oxide clusters and small molecules can provide molecular level mechanisms to understand the excellent activity of gold supported by metal oxides. While the promotion role of gold in alkane transformation was identified in the clusters with atomic oxygen radicals (O^?.), the role of gold in the systems without O^?. is not clear. By employing mass spectrometry and quantum chemistry calculations, the reactivity of Au₂VO₃⁺ clusters with closed‐shell electronic structures toward ethane was explored. Both the dehydrogenation and ethene elimination channels were identified. It is gold rather than oxygen species initiating the C?H activation. The Au?Au dimer formed during the reactions plays important roles in ethane transformation. The reactivity comparison between Au₂VO₃⁺ and bare Au₂⁺ demonstrates that Au₂VO₃⁺ not only retains the property of bare Au₂⁺ that transforming ethane to dihydrogen, but also exhibits new functions in converting ethane to ethene, which reveals the importance of the composite system. This study provides a further understanding of the reactivity of metal oxide supported gold in alkane activation and transformation.     

Adsorption of Propene on Neutral Gold Clusters in the Gas Phase

The adsorption of propene on neutral gold clusters is investigated in a collision cell under a few collision conditions. The adsorption reaction is studied by pressure‐dependent kinetic measurements and delayed unimolecular dissociation of the excited Au_n?propene complexes. The cluster size (n=9–25) and temperature (T=90–300 K) dependence of the propene adsorption is analyzed. Strong size dependences of the absorption reaction are observed; a larger propene adsorption probability was found for gold clusters composed of an even number of atoms. Propene binding energies are estimated by comparison of the temperature‐dependent unimolecular dissociation rates with rates obtained by using statistical RRKM modeling. The Au_n–propene binding energies decrease non‐monotonously with cluster size and are in the range of 1.2–0.85 eV for n=9–25. Finally, the bonding of C₃H₆ on Au_n is qualitatively described and similarities with the absorption of CO molecules on gold clusters are discussed.     

Predicting Stable Molecular Structures for (RNC)2AuIX Complexes

Calculations have been performed at the MP2 and DFT levels for investigating the reasons for the difficulties in synthesizing bis(isocyanide)gold(I) halide complexes. Three‐coordinated gold(I) complexes of the type (R₃P)₂Au^IX ( 1 ) can be synthesized, whereas the analogous isocyanide complexes (RNC)₂Au^IX ( 2 ) are not experimentally known. The molecular structures of (R₃P)₂Au^IX (X = Cl, Br, and I) and (RNC)₂Au^IX with X = halide, cyanide, nitrite, methylthiolate, and thiocyanate are compared and structural differences are discussed. Calculations of molecular properties elucidate which factors determine the strength of the gold‐ligand interactions in (RNC)₂Au^IX. The linear bonding mode of RNC favors a T‐shaped geometry instead of the planar Y‐shaped trigonal structure of (R₃P)₂Au^IX complexes that have been synthesized. An increased polarity of the Au–X bond in 2 leads to destabilization of the Y‐shaped structure. Chalcogen‐containing ligands or cyanide appear to be good X‐ligand candidates for synthesis of (RNC)₂Au^IX complexes.     

Synthese und Kristallstruktur des Goldclusters [Au16(AsPh3)8Cl6]

Synthesis and Structures of the Gold Cluster [Au₁₆(AsPh₃)₈Cl₆] Reduction of Ph₃AsAuCl with NaBH₄ in ethanol yields the gold cluster [Au₁₆(AsPh₃)₈Cl₆]. It can be crystallized from dichloromethane/diisopropyl ether in form of dark red, light sensitive crystals with the space group P2₁/n and a = 1777.68(8), b = 3372.7(1), c = 2696.2(1)pm, β = 94.166(6)°, Z = 4). The inner skeleton of the 16 Au atoms consists of a centered icosahedron of which one of the corners binds to three additional Au atoms forming a tetrahedron pendent. The shortest Au–Au distances of 264.3 to 266.6 pm correspond to the bonds to the three external Au atoms. Within the icosahedron the distances between the central atom and the peripheral atoms (273.0–279.1 pm) are distinctly shorter than the distances between the peripheral atoms (283.6–299.0 pm).     

Same Magic Number but Different Arrangement: Alkynyl‐Protected Au25 with D3 Symmetry

Two homoleptic alkynyl‐protected gold clusters with compositions of Na[Au₂₅(C≡CAr)₁₈] and (Ph₄P)[Au₂₅(C≡CAr)₁₈] (Na? 1 and Ph₄P? 1 , Ar=3,5‐bis(trifluoromethyl)phenyl) were synthesized via a direct reduction method. 1 is a magic cluster analogous to [Au₂₅(SR)₁₈]^? in terms of electron counts and metal‐to‐ligand ratio. Single‐crystal structure analysis reveals that 1 has an identical Au₁₃ kernel to [Au₂₅(SR)₁₈]^?, but adopts a distinctly different arrangement of the six peripheral dimer staple motifs. The steric hindrance of alkynyl ligands is responsible for the D₃ arrangement of Au₂₅. The introduction of alkynyl also significantly changes the optical absorption features of the nanocluster as supported by DFT calculations. This magic cluster confirms that there is a similar but quite different parallel alkynyl‐protected metal cluster universe in comparison to the thiolated one.     

Ionic bonding of lanthanides,as influenced by d‐ and f‐atomic orbitals,by core–shells and by relativity

Lanthanide trihalide molecules LnX₃ (X = F, Cl, Br, I) were quantum chemically investigated, in particular detail for Ln = Lu (lutetium). We applied density functional theory (DFT) at the nonrelativistic and scalar and SO‐coupled relativistic levels, and also the ab initio coupled cluster approach. The chemically active electron shells of the lanthanide atoms comprise the 5d and 6s (and 6p) valence atomic orbitals (AO) and also the filled inner 4f semivalence and outer 5p semicore shells. Four different frozen‐core approximations for Lu were compared: the (1s²–4d¹⁰) [Pd] medium core, the [Pd+5s²5p⁶ = Xe] and [Pd+4f¹⁴] large cores, and the [Pd+4f¹⁴+5s²5p⁶] very large core. The errors of Lu? X bonding are more serious on freezing the 5p⁶ shell than the 4f¹⁴ shell, more serious upon core‐freezing than on the effective‐core‐potential approximation. The Ln? X distances correlate linearly with the AO radii of the ionic outer shells, Ln³⁺‐5p⁶ and X^?‐np⁶, characteristic for dominantly ionic Ln³⁺‐X^? binding. The heavier halogen atoms also bind covalently with the Ln‐5d shell. Scalar relativistic effects contract and destabilize the Lu? X bonds, spin orbit coupling hardly affects the geometries but the bond energies, owing to SO effects in the free atoms. The relativistic changes of bond energy BE, bond length R_e, bond force k, and bond stretching frequency v_s do not follow the simple rules of Badger and Gordy (R_e～BE～k～v_s). The so‐called degeneracy‐driven covalence, meaning strong mixing of accidentally near‐degenerate, nearly nonoverlapping AOs without BE contribution is critically discussed. © 2015 Wiley Periodicals, Inc.     

Hexanuclear Gold(I) Phosphide Complexes as Platforms for Multiple Redox‐Active Ferrocenyl Units

The synthesis, X‐ray crystal structures, electrochemical, and spectroscopic studies of a series of hexanuclear gold(I) μ₃‐ferrocenylmethylphosphido complexes stabilized by bridging phosphine ligands, [Au₆(P?P)_n(Fc‐CH₂‐P)₂][PF₆]₂ (n=3, P?P=dppm (bis(diphenylphosphino)methane) ( 1 ), dppe (1,2‐bis(diphenylphosphino)ethane) ( 2 ), dppp (1,3‐bis(diphenylphosphino)propane) ( 3 ), Ph₂PN(C₃H₇)‐PPh₂ ( 4 ), Ph₂PN(Ph‐CH₃‐p)PPh₂ ( 5 ), dppf (1,1′‐bis(diphenylphosphino)ferrocene) ( 6 ); n=2, P?P=dpepp (bis(2‐diphenylphosphinoethyl)phenylphosphine) ( 7 )), as platforms for multiple redox‐active ferrocenyl units, are reported. The investigation of the structural changes of the clusters has been probed by introducing different bridging phosphine ligands. This class of gold(I) μ₃‐ferrocenylmethylphosphido complexes has been found to exhibit one reversible oxidation couple, suggestive of the absence of electronic communication between the ferrocene units through the Au₆P₂ cluster core, providing an understanding of the electronic properties of the hexanuclear Au^I cluster linkage. The present complexes also serve as an ideal system for the design of multi‐electron reservoir and molecular battery systems.     

Trinuclear Gold Clusters Supported by Cyclic (alkyl)(amino)carbene Ligands: Mimics for Gold Heterogeneous Catalysts

The synthesis of air‐ and moisture‐stable trinuclear mixed‐valence gold(I)/gold(0) clusters is described. They promote the catalytic carbonylation of amines under relatively mild conditions. The synthetic route leading to the trinuclear clusters involves a simple ligand exchange from the readily available μ³‐oxo‐[(Ph₃PAu)₃O]⁺ complex. This synthetic method paves the way for the preparation of a variety of mixed‐valence gold(I)/gold(0) polynuclear clusters. Moreover, the well‐defined nature of the complexes demonstrates that the catalytic process involves a rare example of a definite change of oxidation state of gold from Au⁰₂Au^I to Au^I₃.     

[μ‐4,5‐Bis(diphenylphosphino)‐9,9‐dimethylxanthene]bis[(trifluoroacetato)gold(I)] and its dichloromethane 0.58‐solvate

The dinuclear Au^I complex containing the 4,5‐bis(diphenylphosphino)‐9,9‐dimethylxanthene (xantphos) ligand and trifluoroacetate anions exists in a solvent‐free form, [μ‐4,5‐bis(diphenylphosphino)‐9,9‐dimethylxanthene]bis[(trifluoroacetato)gold(I)], [Au₂(C₂F₃O₂)₂(C₃₉H₃₂OP₂)], (I), and as a dichloromethane solvate, [Au₂(C₂F₃O₂)₂(C₃₉H₃₂OP₂)]·0.58CH₂Cl₂, (II). The trifluoroacetate anions are coordinated to the Au^I centres bridged by the xantphos ligand in both compounds. The Au^I atoms are in distorted linear coordination environments in both compounds. The phosphine substituents are in a syn arrangement in the xantphos ligand, which facilitates the formation of short aurophilic Au...Au interactions of 2.8966 (8) Å in (I) and 2.9439 (6) Å in (II).