Au-Au Distances Research Articles

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.

Crystal structure of a pentanuclear gold-silver cluster complex

The title compound, [C16H36N]+[C48H30Au3Ag2]−, crystallizes in the triclinic space groupP1−1, witha=18.199(12),b=19.210(8),c=19.270(9)A,α=71.34(3)°β=76.43(4)° γ=72.95(5)° andZ=4, with two independent molecules in the asymmetric unit. The structure was solved by direct methods and refined by full-matrix least squares methods toR=0.072 for 3739 observed reflections. The metal atoms have a trigonal-bipyramidal arrangement with the three Au atoms forming an equilateral triangle and two Ag atoms occupying apical positions. Each Au atom is σ-bonded to phenylethynyl ligands in a linear coordination. Each Ag atom is asymmetrically pi-bonded to three alkyne groups. The Au-Au distances lie in the range of 3.934–4.010 A, indicating the lack of Au-Au bond.

Length distributions in metallic alloys.

We use the embedded-atom potential of Johnson to compute the length-distribution functions for a large number of fcc binary metallic alloys. From these distributions, we extract the mean lengths of the nearest-neighbor bonds, which compare well with recent extended x-ray-absorption fine-structure (EXAFS) experiments in ${\mathrm{Ni}}_{\mathit{x}}$${\mathrm{Au}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$. In other cases, where EXAFS results are not available, we compare our results with the mean lattice parameter as determined by diffraction experiments. While the embedded-atom potential is accurate for some alloys (e.g., Ni-Au), we show that for alloys containing Pt, a simple central-force model is superior. The embedded-atom potential of Johnson predicts an unexpected contraction of the Au-Au distance in Ag-rich Au-Ag alloys. We point out that an important characteristic of any alloy potential is its ability to get the single and double defects correct.

A luminescent gold complex: bis-μ-[bis(dicyclohexylphosphino)ethane-P,P']-digold bis(hexafluorophosphate)

[Au_2(C_(26)H_(48)P_2h](PF_6)_2, M_r = 1529·1, tetragonal, P4n2, ɑ= 15·917 (5), c = 12-448 (1) A, V = 3154 (1) A3 , Z = 2, Dx = 1·61 g cm^(-3), λ(Mo Ka) = 0·71073 A, μ = 50·1 cm^(-1), F(000) = 1528, room temperature (297 K), R = 0·064 for 3525 reflections with F/_o^2 > 0,0·038 for 2440 with F/_o^2 > 3σ(F/_o^2). This [Au_2(C_26)H_(48)P_2)_2] (PF_6)_2 compound shows a strong luminescence in the solid state at 77 K. The cation consists of two Au atoms joined by two bis (dicyclohexylphosphino )ethane links, with one Au atom and one half of a link being the asymmetric unit. The Au-Au distance [2·936 (1) A] is only slightly longer than the 2·884 A found in gold metal, indicative of substantial metal-metal bonding.

Au/Si(111): Analysis of the ( sqrt 3 x sqrt 3 )R30 degrees and 6 x 6 structures by in-plane x-ray diffraction.

In-plane, fractional-order diffraction-data sets from thin Au layers on Si(111) with (\ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 )R30\ifmmode^\circ\else\textdegree\fi{} and 6\ifmmode\times\else\texttimes\fi{}6 structures were measured at the wiggler beamline W1 at the Hamburg synchrotron radiation laboratory. For the \ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 structure the trimer model is confirmed with an Au-Au distance of 2.8 \AA{}. In the \ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 unit cell, two additional sites beside the Au trimer were found which can be identified with distorted substrate layers or additional partially occupied Au sites. The 6\ifmmode\times\else\texttimes\fi{}6 structure is a sixfold twinned structure. The observed Patterson function clearly indicates the main features of the structural units. Each consists of three trimer clusters of Au atoms, forming a nearly equilateral triangle. The local structure of each trimer is either the original \ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 structure or a twin structure where the Au trimers are rotated by 60\ifmmode^\circ\else\textdegree\fi{}. Three of these structural units form the 6\ifmmode\times\else\texttimes\fi{}6 unit cell. Model calculations with incoherent superposition of twin domains lead to Patterson maps very similar to the one observed.

Metallization and phase transitions of the three-dimensional halogen-bridge mixed-valence complex Cs 2Au 2I 6 under high pressure

We have recently shown that insulating mixed-valence complex Cs 2Au 2I 6 transforms gradually toa metallic state between ambient pressure and 4.5 GPa at room temperature. Also shown that Cs 2Au 2I 6 undergoes a metal-to-metal transition in a process of increasing temperature at 6.5 GPa. The present energy-dispersive X-ray diffraction study has revealed that Cs 2Au 2I 6 undergoes a pressure-induced first-order tetragonal-to-tetragonal phase transition at about 5.5 GPa and room temperature. At the transition pressure, the Au-Au distance elongates along the c-axis, which is due to the ‘band Jahn-Teller’ transition. The Au 11 valence state is considered to be realized at this pressure. This phase transition would relate to the minimum in the pressure-resistance curve near 5.5 GPa, previously reported. It was also found that Cs 2Au 2I 6 undergoes a first-order tetragonal-to-cubic phase transition at 6.8 GPa and T ∾ 350 K.

Static lattice distortions and the structure of Au/Si(111)-(5 x 1): An x-ray-diffraction study.

Grazing-incidence x-ray diffraction has been used to determine the atomic arrangement in the 5\ifmmode\times\else\texttimes\fi{}1 structure of Au on Si(111). The main features of this structure are partially occupied rows of gold atoms in low-symmetry sites. The density of Au atoms is highly asymmetric in the direction perpendicular to the rows. The substrate atoms in the top double layer are shifted up to 1 \AA{} from their bulk position. The structure has a disordered 5\ifmmode\times\else\texttimes\fi{}2 periodicity due to the variation of the interatomic Au-Au distances within a row in the [011\ifmmode\bar\else\textasciimacron\fi{}] direction. The model is consistent with recent scanning-tunneling-microscopy topographs.

Structure analysis of high-pressure metallic state of the three-dimensional mixed-valence compound Cs2AuIAuIIII6 by X-ray diffraction using SR

The present energy-dispersive X-ray diffraction study has revealed that Cs2Au2I6 undergoes a pressure-induced first-order tetragonal-tetragonal phase transition at about 5.5 GPa and room temperature. At the transition pressure, the Au-Au distance elongates along the c-axis. This phase transition would relate to the resistance minimum at 5.4 GPa, previously reported [1]. It was also found that Cs2Au2I6 undergoes a first-order tetragonal-cubic phase transition at 6.5 GPa and T≈350 K.

An exafs study of the cluster molecule Au 55(PPh 3) 12Cl 6

Gold L 3 edge EXAFS has been used to study the coordination environment of gold atoms in the cluster molecule Au 55( PPh 3) 12 Cl 6. The mean coordination of 7 by other gold atoms is consistent with a 3-shell cuboctahedral structure for the Au 55 cluster. The first direct measurement of the Au-Au distance in this cluster shows that the spacing is significantly shorter than that in bulk metallic gold and is consistent with calorimetric work which has shown the Au-Au interactions are stronger in the cluster than in bulk gold. There is no evidence to suggest a significant spread of Au-Au distances in Au 55( PPh 3) 12 Cl 6, in contrast to lower-nuclearity gold cluster molecules which have peripheral Au-Au distances typically 0.2C̊ longer than those to interstitial gold atoms.

Darstellung und kristallstruktur von K 4Au 6S 5 — ein thioaurat mit anionischen [Au 6S 5]-baugruppen

The new compound K 4Au 6S 5 was prepared by reacting a corresponding mixture of potassium sulphide, gold and sulphur at 600 °C. Green-yellow crystals were obtained by cooling the melt slowly. The crystal structure was determined from four-circle diffractometer data and refined to a conventional R of 0.037 for 342 observed reflections. K 4Au 6S 5 crystallizes in the space group P6̄2c with a = 9.631(3) A ̊ , c = 9.856(4) A ̊ and Z = 2. The crystal structure is characterized by anionic [Au 6S 5] groups, stacked along [001] in hexagonal close-packed sense. They are built up from trigonal bipyramids of sulphur atoms, upon whose skew edges lie the gold atoms, so forming a trigonal prism. The coordination of the gold atoms is almost linear. The Au-Au distances within and between the [Au 6] units show weak interactions of the atoms with d 10 configuration.

Atom hopping on small gold particles imaged by high-resolution electron microscopy

Atom hopping on small gold particles imaged by high-resolution electron microscopy

Structure and bonding in Au 2Os mixed-metal carbonyl clusters: the crystal and molecular structure of [Os(CO) 4AuPPh 32

An X-ray analysis of [Os(CO) 4AuPPh 3 2] shows that the metal atoms define an isosceles triangle in which the Au-Au distance is 2.929(1) Å, which is ca. 0.1 Å shorter than in the corresponding iron analogue [Fe(CO) 4AuPPh 3 2].

Crystal growth and the crystal structures of two modifications of gold monobromide, I-AuBr and P-AuBr

Single crystals of two modifications of AuBr, called P-AuBr and I-AuBr, were prepared by a vapour-transport method. I-AuBr is isostructural with AuCl; it is tetragonal with a = 6.940 A ̊ , c = 9.252 A ̊ , space group I4 1/ amd, Z = 8. P-AuBr is isostructural with Aul; it is tetragonal with a = 4.296 A ̊ , c = 12.146 A ̊ , space group P4 2/ ncm, Z = 4. The structures consist of zigzag chains of Au and Br with symmetry mm. Au is linearly coordinated to Br at distances of 2.40Å in I-AuBr and 2.44Å in P-AuBr; the bond angles Au-Br-Au are 92.3° and 77.1°, respectively. The bromine atoms and gold atoms in P-AuBr form square planar nets perpendicular to the c axis with the dimensions 4.30 A ̊ × 4.30 A ̊ and 3.04 A ̊ × 3.04 A ̊ , respectively, for bromine and gold layers; the Au-Au distance inside the chain is equal to the distance between gold atoms of different chains in the same layer. The sequence of layers of Au and Br is Au/Br/Br/ Au/Br/Br/Au. Therefore P-AuBr can also be considered as a layered compound.

ChemInform Abstract: AN OCTAHEDRAL GOLD CLUSTER, CRYSTAL AND MOLECULAR STRUCTURE OF HEXAKIS‐(TRIS‐(P‐TOLYL)PHOSPHINE)‐OCTAHEDRO‐HEXAGOLD BIS(TETRAPHENYLBORATE)

The crystal arid molecular structure of the title compound has been determined from three-dimensional X-ray data collected by counter methods and refined by least-squares to R 0·052 from 3501 independent reflections. Crystals are triclinic, space group P, with unit cell dimensions a= 17·48(2), b= 19·02(2), c= 13·81(1)A, α= 101·1 (1), β= 94·2(1), γ= 116·4(1)°, Z= 1. The hexanuclear dication is a centrosymmetric octahedron significantly distorted. Two mutually opposite faces have edges ranging from 2·932(2) to 2·990(2), the remaining edges ranging from 3·043(2) to 3·091 (2)A. The overall mean Au-Au distance, 3·019 A, is longer than the corresponding values in Au11 and Au9 clusters. These long distances do not arise from non-bonding repulsions between adjacent ligands.

An octahedral gold cluster: crystal and molecular structure of hexakis[tris-(p-tolyl)phosphine]-octahedro-hexagold bis(tetraphenylborate)

The crystal arid molecular structure of the title compound has been determined from three-dimensional X-ray data collected by counter methods and refined by least-squares to R 0·052 from 3501 independent reflections. Crystals are triclinic, space group P, with unit cell dimensions a= 17·48(2), b= 19·02(2), c= 13·81(1)A, α= 101·1 (1), β= 94·2(1), γ= 116·4(1)°, Z= 1. The hexanuclear dication is a centrosymmetric octahedron significantly distorted. Two mutually opposite faces have edges ranging from 2·932(2) to 2·990(2), the remaining edges ranging from 3·043(2) to 3·091 (2)A. The overall mean Au-Au distance, 3·019 A, is longer than the corresponding values in Au11 and Au9 clusters. These long distances do not arise from non-bonding repulsions between adjacent ligands.