Ultra-Thin Gold Cluster Films by Langmuir–Blodgett-Techniques

The extraordinary electronic properties of the full-shell cluster Au₅₅(PPh₃)₁₂Cl₆ and its ligand modified derivatives make them one of the most attractive building blocks in future nanoelectronics. The reason is the ability to act as a single electron switch or transistor at room temperature. As a consequence of this knowledge, further developments to organize these quantum dots in two dimensions are necessary. In this study, the Langmuir–Blodgett (LB) technique has been applied to generate extended two-dimensionally organized arrangements of Au₅₅(PPh₃)₁₂Cl₆, Au₅₅[(cyclopentyl)₇Si₈O₁₂(CH₂)₃SH]₁₂Cl₆ and of Au₅₅(PhSH) _x Cl₆. Film formation was performed by spreading dichloromethane or pentane solutions of the clusters onto the water surface in a LB trough, followed by compression by means of a film balance. From the π-A isotherms exact cluster dimensions could be calculated from monolayers, except for Au₅₅[(cyclopentyl)₇Si₈O₁₂(CH₂)₃SH]₁₂Cl₆, the size of which resulted as too small. The reason is to be seen in the formation cluster double layers. Brewster angle microscopy (BAM) investigations of the thin films on the water surface, atomic force microscopy (AFM) and transmission electron microscopy (TEM) studies of transferred films clearly demonstrated formation of densely packed monolayers and of double layers, respectively. These extended mono- and double layers are now available for electric investigations and the construction of layered systems. Those works are in progress. Dedicated to Professor Ilya Moiseev on the occasion of his 75th birthday.     

Electronic structure and bonding of the metal cluster compound Au55(PPh3)12Cl6

We discuss the electronic structure, bonding and physical properties of the gold cluster compound Au₅₅(PPh₃)₁₂Cl₆. Results from our experimental measurements, including EXAFS, specific heat, Mössbauer, UV-visible and photoelectron spectroscopy, are combined with those of other work to form a consistent physical picture of the system. The bonding in Au₅₅(PPh₃)₁₂Cl₆ is much more delocalised and non-directional than in smaller gold cluster molecules. The Au₅₅ cluster exhibits a substantial degree of metallic bonding, while displaying some of the characteristics of a discrete energy level spectrum.     

The thermal motion of gold atoms in metal cluster compounds as determined by Mössbauer and specific heat

¹⁹⁷Au Mössbauer effect spectroscopy and specific heat measurements have been performed as a function of temperature on three gold polynuclear cluster compounds, [Au₉(PPh₃)₈](NO₃)₃, Au₁₁(PPh₃)₇(SCN)₃, and Au₅₅(PPh₃)₁₂Cl₆. The Mössbauer data yield information on the vibrational motions of the various distinguishable Au sites, as well as on the motion of the clusters as a whole. The Mössbauer and the specific heat data are successfully described by a superposition of inter- and intra-cluster vibrations. The latter are determined by calculating numerically the normal modes of vibration of the metal cores.     

The relationship of Au55(PPh3)12Cl6 to colloidal gold

The electronic (UV-visible) spectrum of the molecular cluster Au₅₅(PPh₃)₁₂Cl₆ shows features corresponding to the 520 nm plasma resonance and the shorter-wavelength interband transition of colloidal gold. These absorptions differ qualitatively from the simpler one-electron transitions of lower-nuclearity cluster molecules. Differential scanning calorimetry has been used to measure the enthalpy of decomposition of Au₅₅(PPh₃)₁₂Cl₆. The Au-Au bonding appears to be substantially stronger than in bulk gold.     

Differenz-Scanning-Kalorimetrische-Untersuchungen an großen Übergangsmetallclustern

Differential Scanning Calorimetric Investigations of Large Transition Metal Clusters The thermal behavior of various ligand stabilized transition metal clusters is investigated by means of differential-scanning-calorimetry (DSC). In the case of the cluster Au₅₅(PPh₃)₁₂Cl₆ the decomposition temperature of 131°C, the decomposition enthalpy of 114 J/g, as well as the bond energy of 75.6 kJ/mole can be determined. Moreover, detailed informations about the mechanism of cluster degradation into Ph₃PAuCl, (Ph₃P)₂AuCl, PPh₃, and metallic gold can be made in combination with impedance spectroscopic measurements. The derivatives Au₅₅[P(p-tolyl)₃]₁₂Cl₆ and Au₅₅[P(p-anisyl)₃]₁₂Cl₆ behave similar like the PPh₃ substituted clusters. The thermolysis of the water-soluble cluster Au₅₅(TPPMS-Na)₁₂Cl₆ proceeds completely different, what can be attributed to the formation of (TPPMS-Na)Au(TPPMS). The DSC diagram of the platinum cluster Pt₃₀₉phen*₃₆O₃₀ shows no decomposition signal between 25 and 400°C although degradation occurs. This must be due to compensating processes of unknown nature. The thermal behavior of the larger 5-, 7-, and 8-shell palladium clusters documents the relation to the metallic state. The points of decomposition are found between 130 and 115°C, the decomposition enthalphies between 150 and 60 J/g, and the bond energies between 58–56 kJ/mole what is slightly smaller than in the bulk metal with 62.8 kJ/mole.     

NMR of metal-core bonded31P in polynuclear metal cluster compounds

In this paper we present measurements of nuclear relaxation times of³¹P in the polynuclear cluster compounds Au₅₅(PPh₃)₁₂Cl₆ and Ru₅₅(P(t-Bu)₃)₁₂Cl₂₀. Above 15 K the data can be described as a Korringa process, while below 15 K the relaxation time appears to be thermally activated.     

Synthesis, Stability, and Photoluminescence Properties of PdAu10(PPh3)8Cl2 Clusters

We report on the synthesis, stability, and photoluminescence (PL) properties of triphenylphosphine (PPh₃)-stabilized PdAu₁₀(PPh₃)₈Cl₂ cluster, which is a mono-Pd-doped cluster of the well-studied Au₁₁(PPh₃)₈Cl₂ cluster. The PdAu₁₀(PPh₃)₈Cl₂ cluster was synthesized by simultaneously reducing two different metal complexes; AuCl(PPh₃) and Pd(PPh₃)₄. Experimental evaluation of the stability showed that PdAu₁₀(PPh₃)₈Cl₂ is more stable against degradation in solution than the monometal Au₁₁(PPh₃)₈Cl₂ cluster. PL measurements revealed that PdAu₁₀(PPh₃)₈Cl₂ exhibits PL at 950?nm with a quantum yield of 1.5?×?10^?3, which has not been observed for the monometal Au₁₁(PPh₃)₈Cl₂ cluster. The results indicate that Pd doping is a powerful method to produce clusters with higher stability and different physical properties than the monometal Au:PPh₃ clusters.     

Generation and electrical contacting of gold quantum dots

We report on first tries in generating a system of 20-nm-wide parallel bars as templates for conductive gold wires, decorated with Au₅₅(PPh₃)₁₂Cl₆ clusters. The electrical characterization of these quasi one-dimensional arrangements shows pronounced nonlinearity, reflecting charging effects on the small clusters. Furthermore, very first results on the generation of 2.5-nm bars are also reported.     

Synthesis, single crystal X-ray analysis, and TEM for a single-sized Au11 cluster stabilized by SR ligands: The interface between molecules and particles

An SR-modified Au cluster with a sub-nanometer size, Au₁₁(S-4-NC₅H₄)₃(PPh₃)₇ (1), has been synthesized by NaBH₄ reduction of Au(S-py)(PPh₃) or by reacting [Au₉(PPh₃)₈](NO₃)₃ with HS-4-py in good yield. Its molecular structure has been elucidated by single crystal X-ray diffraction, and TEM observation has been achieved for the first time for this size of SR-modified Au clusters. The core structure is best described in terms of an incomplete icosahedron. CV measurements in CH₂Cl₂ have suggested that the cluster does not coagulate in solution with significant concentration.     

An EXAFS study of some gold and palladium cluster compounds

Gold L₃-edge EXAFS measurements at 80 K on Au₅₅(PPh₃)₁₂Cl₆ confirm that the Au-Au distances in this amorphous metal cluster compound are significantly shorter than in bulk gold. The nearest-neighbour Au-Au distances are all equal within experimental uncertainty. Outer-shell Au-Au distances have also been resolved. The results are consistent with the cuboctahedral structure originally proposed for this cluster, but not the polyicosahedral one recently suggested. Very similar results have been obtained from the sulphonated water-soluble derivative Au₅₅(PPh₂C₆H₄SO₃Na)₁₂Cl₆. In contrast, EXAFS of Au₁₁{PPh₂(p-ClC₆H₄)}₇I₃ has clearly resolved the two nearest-neighbour Au-Au distances associated with its icosahedral structure.Palladium K-edge EXAFS has been used to study the cluster Pd₅₆₁(phen)₃₆O₂₀₀. The Pd-Pd distance is nearly equal to that in bulk palladium. The results show a cubic close-packed cluster structure for this material, in contrast to the icosahedral structure reported for Pd₅₆₁(phen)₆₀(OAc)₁₈₀.     

Secondary ion mass spectra of gold super clusters up to 140000 dalton

The bombardment of a two-shell gold complex (Au₅₅(PPh₃)₁₂Cl₆) with 10 keV Xe⁺-ions results in the formation of secondary ion masses up to 140000 u. These are by far the largest secondary ions observed under primary particle bombardment. The detection and identification of these ions with a Time-Of-Flight Secondary Ion Mass Spectrometer (TOF-SIMS) gives important information about the behavior of naked full-shell clusters. Au₁₃ particles, generated from the Au₅₅ cluster, serve as building blocks for a series of super-clusters up to (Au₁₃)₅₅. The results for keV-ion bombardment are compared to those for MeV-ion bombardment.     

Partial Phosphorization: A Strategy to Improve Some Performance(s) of Thiolated Metal Nanoclusters Without Notable Reduction of Stability

Thiolates endow metal nanoclusters with stability while sometimes inhibit the catalytic activity due to the strong M−S interaction (M: metal atom). To improve the catalytic activity and keep the stability to some extent, one strategy is the partial phosphorization of thiolated metal nanoclusters. This is demonstrated by successful partial phosphorization of Au₂₃(SC₆H₁₁)₁₆ and by revealing that the products Au₂₂(SC₆H₁₁)₁₄(PPh₃)₂ and Au₂₂(SC₆H₁₁)₁₂(PPh₃)₄, with varied degree of phosphorization, both show excellent activity in the photocatalytic oxidation of thioanisole without notable reduction of stability. Furthermore, Au₂₂(SC₆H₁₁)₁₂(PPh₃)₄ exhibits better photoluminescence performance than the mother nanocluster Au₂₃(SC₆H₁₁)₁₆, indicating that partial phosphorization can also improve some other performance(s) except for the catalytic performance. The intermediates Au_22-xCu_x(SC₆H₁₁)₁₂(PPh₃)₄ (x=1, 2) in the transformation from Au₂₃(SC₆H₁₁)₁₆ (Au₂₂(SC₆H₁₁)₁₄(PPh₃)₂) to Au₂₂(SC₆H₁₁)₁₂(PPh₃)₄ were captured and identified by mass spectrometry and single crystal X-ray diffraction, which throws light on the understanding of the non-alloyed anti-galvanic reaction.     

Synthesis of bridged and linked ruthenium and osmium carbonyl clusters containing a [Au2(Ph2PCH2CH2PPh2)]2+ unit. The crystal and molecular structures of Ru5C(CO)14Au2(Ph2PCH2CH2PPh2) and {Os4H3(CO)12}2Au2(Ph2PCH2CH2PPh2)

Treatment of Au₂(Ph₂PCH₂CH₂PPh₂)Cl₂ with one equivalent of the [Ru₅C(CO)₁₄]²⁻ dianion in the presence of TlPF₆ gives Ru₅C(CO)₁₄Au₂(Ph₂PCH₂CH₂PPh₂) (1) in good yield and the [{Ru₅C(CO)₁₄}₂Au₂(Ph₂PCH₂CH₂PPh₂)]²⁻ (2) anion in low yield. Complex 2 becomes the major product if 2 equivalents of [Ru₅C(CO)₁₄]²⁻ are used. Reaction of [Au₂(Ph₂PCH₂CH₂PPh₂)Cl₂] with 3 equivalents of [H₃Os₄(CO)₁₂]⁻ anion in the presence of TlPF₆ affords {H₃Os₄(CO)₁₂}₂Au₂(Ph₂PCH₂CH₂PPh₂) (3) in reasonable yield. X-ray diffraction studies of 1 and 3 show that they contain the [Au₂(Ph₂PCH₂CH₂PPh₂)]²⁺ fragment in different coordination modes.     

Synthesis and molecular structure of [Au3Ru4(μ3-H)(CO)12(PPh3)3]

The title compound can be prepared in good yield by heating either [Ru₄(μ-H)₄(CO)₁₂] or [Au₂Ru₄(μ₃-H)₂(CO)₁₂(PPh₃)₂] with [AuMe(PPh₃)] in toluene. The related compound [Au₃Ru₄(μ₃-H)(μ-dppm)(CO)₁₂(PPh₃)] has also been prepared. Both trigoldtetraruthenium clusters undergo dynamic behaviour in solution, involving intramolecular rearrangement of the metal core, as revealed by variable temperature NMR studies. The crystal structure of [Au₃Ru₄(μ₃-H)(CO)₁₂(PPh₃)₃] has been established by an X-ray diffraction study. The metal atom core comprises a trigonal bipyramidal AuRu₄ unit with two AuRu₂ faces capped by gold atoms.     

Physical and Chemical Consequences of Size-Reduction of Gold: Bioresponse and Biodistribution

The article is dealing with the dependency of physical and chemical properties on size and coating of gold nanoparticles (Au NPs) and their potential in medicine. Full-shell clusters of the type Au₅₅(PR₃)₁₂Cl₆ are in the focal point due to their special properties. They act as quantum dots at room temperature and their stability is based on the perfect cuboctahedral structure. The bioresponse of the 1.4 nm Au₅₅ clusters is, compared with smaller and larger Au NPs, very special, indicated by high cytotoxicity. It is caused by oxidative stress in cells accompanied by direct interactions with DNA. Biodistribution in Wistar–Kyoto rats differs also characteristically from larger Au NPs. Larger Au NPs, intravenously injected, assemble almost quantitatively in the liver, whereas Au₅₅ clusters distribute over numerous other organs. All comparisons have been carried out by Au species with identical ligand molecules in order to have the same conditions concerning surface behaviour.     

Synthese,Kristallstruktur und spektroskopische Charakterisierung von [Au12(PPh)2(P2Ph2)2(dppm)4Cl2]Cl2

Synthesis, Crystal Structure and Spectroscopic Characterization of [Au₁₂(PPh)₂(P₂Ph₂)₂(dppm)₄Cl₂]Cl₂ The reaction of [(AuCl)₂dppm] (dppm = Ph₂PCH₂PPh₂) with P(Ph)(SiMe₃)₂ in CHCl₃ results in the formation of [Au₁₂(PPh)₂(P₂Ph₂)₂(dppm)₄Cl₂]Cl₂ ( 1 ), the crystal structure of which was determined by single crystal X‐ray analysis (space group P2₁/c, a = 1425.3(3) pm, b = 2803.7(6) pm, c = 2255.0(5) pm, β = 95.00(3)°, V = 8977(3)·10⁶ pm³, Z = 2). The dication in 1 consists of two Au₆P₃ units built by highly distorted Au₃P and Au₂P₂ heterotetrahedra, connected via four bidentate phosphine ligands. Additionally, the compound was characterized by IR‐, UV‐ and NMR spectroscopy. The ³¹P{¹H} NMR spectrum is discussed in detail.     

Metal Ions in Biological Systems,Volume 15: Zinc and its Role in Biology and Nutrition : edited by Helmut Sigel. Marcel Dekker,New York, 1983, ISBN: 0-8247-1750-3, xxii + 493 pages,Sw. Fr. 198.

A single crystal X-ray crystallographic analysis of [ Au₆(PPh₃)₆] (NO₃)₂· 3CH₂Cl₂ has established that the gold atoms adopt the edge-shared bi-tetrahedral structure predicted on the basis of molecular orbital calculations.     

Low-temperature specific heat of the cluster compound Au55 (P(C6H5)3)12Cl6

Specific-heat measurements on the cluster compound Au₅₅(P(C₆H₅)₃)₁₂Cl₆ at temperatures 0.06 K ≤T≤3 K and in magnetic fields 0≤B≤6 T are reported. While above 0.6 K the specific heatC is dominated by the inter-cluster vibrational contribution observed previously, an anomalous increase ofC towards lowT is observed below 0.3 K, withC ～T ^?2. This contribution develops into a Schottky-like anomaly forB≥0.4 T, indicating that it might be attributed to local moments which are also observed in ESR measurements. From the height of the anomaly one can infer that approximately one tenth of the Au₅₅ clusters carry a magnetic moment. For 0.6 K≤T≤1 K andB=0 our data indicate the absence of a linear electronic specific-heat contribution expected for bulk Au. This possibly constitutes the first direct observation of the quantum-size effect on electronic energy levels in the specific heat.     

Bis­[bis­(di­phenyl­phosphino­methyl)­phenyl­phosphine]­di­chloro­tetra­gold(I) bis­[chloro­tris­(penta­fluoro­phenyl)­aurate(III)]

The cation of the title compound, [Au₄(PPh₂CH₂PPhCH₂PPh₂)₂Cl₂][Au(C₆F₅)₃Cl]₂ or [Au₄Cl₂(C₃₂H₂₉P₃)₂][AuCl(C₆F₅)₃]₂, displays a rhomboidal geometry for the Au atoms, with short Au?Au distances of 3.104 (2) and 3.185 (1) Å; the linear coordination at the Au^I atoms is distorted: P—Au—P 164.7 (2)° and P—Au—Cl 170.67 (11)°. The anion shows the expected square‐planar geometry at Au^III, with the Au atom 0.022 (5) Å out of the plane of the four donor atoms.     

Synthesen und Kristallstrukturen neuer sulfidoverbrückter Rutheniumclusterverbindungen

Syntheses and Crystal Structures of New Sulfido‐bridged Ruthenium Clusters The reaction of S(SiMe₃)₂ or NaSH with [RuCl₂(PPh₃)₃] or [Ru₃Cl₈(PEt₃)₄] leads to the formation of sulfidobridged ruthenium clusters. In this publication the compounds [Ru₆S₈(PPh₃)₆][PF₆] ( 1 ), [Ru₆S₈(PPh₃)₆][RuCl₄(PPh₃)₂] ( 2 ), [Ru₆S₈(PEt₃)₆] ( 3 ) and [Ru₃S₄Cl₂(PPh₃)₃]₂ ( 4 ) are described. The structures of these compounds were elucidated by single crystal X‐ray structural analyses.