Gold Fragments Research Articles

Elemental analysis through X-ray techniques applied in archeological gold authentication — the case of Transylvanian gold and of the Dacian bracelets

To identify the provenance of gold archeological metallic artifacts, trace elements are more significant than the main components. The most promising elements are Platinum Group Elements (PGE), Sn, Sb, Hg, Pb, Te, and Cu. Several minute fragments of natural Transylvanian gold – placers and primary – were studied by micro Particle Induced X-ray Emission (micro-PIXE) at Forschungszentrum Dresden-Rossendorf, Germany and micro Synchrotron Radiation X-Ray Fluorescence (micro SR-XRF) at ANKA Synchrotron Radiation Facility of the Forschungszentrum Karlsruhe, Germany. The goal of the study was to identify the trace elements characterizing Transylvanian gold, especially Sn, Sb, Pb and Te. A spectacular application of these measurements to the authentication of nine Dacian gold bracelets is presented.

Structure and Bonding in Neutral and Cationic 14‐Electron Gold Alkyne π Complexes

Cyclododecyne (5) as a prototype unstrained alkyne was coordinated to either the neutral [AuCl] fragment or to two different cationic [Au(NHC)](+) entities (NHC = N-heterocyclic carbene), and the resulting complexes 6, 8, and 10 were characterized by X-ray crystallography and NMR spectroscopy. Since the structure of cyclododecyne in the solid state could also be obtained after in situ crystallization, a comparison was possible that provides insights into structural changes imposed on the alkyne by the different gold fragments. These data are interpreted on the basis of a DFT analysis of the bonding situation in the individual compounds, which provides insights into the very first elementary step common to many gold-catalyzed transformations.

Tuning the Photophysical Properties and Solid‐State Organization of Perfluorophenyl‐functionalized Dithieno[3,2‐b:2′,3′‐d]phospholes

AbstractA series of perfluorophenyl‐substituted dithienophosphole derivates has been synthesized. Investigation of their photophysical properties, as well as their organization in the solid state reveals that these properties can be manipulated via introduction of bromine substituents in 2,6‐position of the dithienphosphole scaffold, as well as the complexation of the phosphorus center with an electron rich gold(I) fragment. The strongly electron‐withdrawing character of the perfluorophenyl‐group surmounts the effect of the oxidation of the phosphorus center with respect to photophysics, leading to leading to optoelectronic features similar to those of the trivalent phosphole species. The trivalent phosphole species. The solid‐state organization of the members of this perfluorinated dithienophosphole family, on the other hand, strongly depends on the heteroatoms present within the system, as close intermolecular interactions can be observed between varieties of different atoms (Au‐Au, Br‐Br, Br‐O, Br‐C, F‐C, O‐S), next to regular C‐C π‐stacking interactions.

Trace element fingerprinting of ancient Chinese gold with femtosecond laser ablation-inductively coupled mass spectrometry

In this collaborative investigation, femtosecond laser ablation-inductively coupled mass spectrometry (LA-ICP-MS) was applied to the study of a remarkable group of ancient Chinese gold objects in the Smithsonian's Freer Gallery of Art and Arthur M. Sackler Gallery. Taking advantage of the superior ablation characteristics and high precision of a femtosecond 266 nm Ti:sapphire laser at Lawrence Berkeley National Laboratory, major, minor and trace element concentrations in the gold fragments were quantified. Results validate use of femtosecond LA-ICP-MS for revealing “fingerprints” in minute gold samples. These fingerprints allow us to establish patterns based on the association of silver, palladium and platinum that support historical, technical and stylistic relationships, and shed new light on these ancient objects.

Micro-SR-XRF and micro-PIXE studies for archaeological gold identification – The case of Carpathian (Transylvanian) gold and of Dacian bracelets

Trace-elements are more significant for provenancing archaeological metallic artifacts than the main components. For gold, the most promising elements are platinum group elements (PGE), Sn, Te, Sb, Hg and Pb. Several small fragments of natural Transylvanian gold – placer and primary – were studied by using micro-PIXE technique at the Legnaro National Laboratory AN2000 microbeam facility, Italy and at the AGLAE accelerator, C2RMF, Paris, France and by using micro synchrotron radiation X-ray fluorescence (micro-SR-XRF) at BESSY synchrotron, Berlin, Germany. The goal of the study was to identify the trace-elements, especially Sn, Sb and Te. A spectacular application to five Dacian gold bracelets authentication is presented (Sn and Sb traces).

GILDED ORGANOMETALLICS

The (phosphine)- and (N-heterocyclic carbene)gold(I) fragments are isolobal with the proton; they can attach terminally to fluorescent organic molecules in place of hydrogen. A new synthetic protocol, base-promoted transmetallation, has been developed that binds gold(I) to the peripheries of aromatic molecules through direct C–Au σ-bonds. Photophysical investigations indicate that a single gold center induces triplet excited-state behavior. Gold-induced perturbations of an azadipyrromethene chromophore are also discussed; here gold binds through nitrogen. In all instances considered, gold(I) acts as a relativistic functional group that perturbs its ligands' excited state manifolds through spin-orbit coupling.

Gold–ruthenium compounds containing bridging phosphide or thiolate groups: Crystal structures of the intermediate species [Ru 3(CO) 8L(μ 3-η 2,η 4,η 3-{Me 3SiCC(C 2Fc)SC(Fc)CSC [tbnd]CSiMe 3})] (L = NMe 3 or PPh 2H)

New tetranuclear complexes have been prepared using bridging phosphide or thiolate groups between phosphine gold fragments and the compound [Ru 3(CO) 9(μ 3-η 2,η 4,η 3-{Me 3SiCC(C 2Fc)SC(Fc)CSC CSiMe 3})]. The crystal structures of the intermediates [Ru 3(CO) 8(NMe 3)(μ 3-η 2,η 4,η 3-{Me 3SiCC(C 2Fc)SC(Fc)CSC CSiMe 3})] and [Ru 3(CO) 8(PPh 2H)(μ 3-η 2,η 4,η 3-{Me 3SiCC(C 2Fc)SC(Fc)CSC CSiMe 3})] have been solved.

Synthesis and ligand properties towards gold and silver of the ferrocenylamidobenzimidazole ligand

The treatment of FcCOCl (Fc = (C 5H 5)Fe(C 5H 4)) with aminobenzimidazole in 1:1 or 2:1 ratio gives the ferrocenyl-amido derivatives FcCO(benzimNH 2) or (FcCO) 2(NHbenzim), respectively. The reactivity of FcCO(benzimNH 2) with silver or gold complexes has been studied. The reaction with the basic gold compounds [Au(acac)(PPh 3)] or [O(AuPPh 3) 3]ClO 4 occurs with deprotonation of the NH 2 group and coordination of one or three gold(phosphine) fragments. The treatment of this ligand with silver compounds, such as Ag(OTf) or [Ag(OTf)(PPh 3)], gives the complexes of stoichiometry [Ag(OTf)L] or [Ag(OTf)(PPh 3)L]. The ligand FcCO(benzimNH 2) and the complex [Ag(OTf){FcCO(benzimNH 2)}(PPh 3)] have been characterized by X-ray diffraction studies. DFT calculations were performed on models of this dimeric silver complex and showed that dimerization is energetically favourable, because Ag(I) achieves a four coordination environment, despite some bonds being relatively weak.

A mass spectrometric investigation of the binding of gold antiarthritic agents and the metabolite [Au(CN)2]− to human serum albumin

Electrospray ionisation (ESI) mass spectrometry was used to examine the reactions of the clinically used antiarthritic agent [Au(S2O3)2]3-, and AuPEt3Cl, a derivative of another clinically used agent auranofin, with human serum albumin (HSA) obtained from a human volunteer. Both compounds reacted readily with HSA to form complexes containing one or more covalently attached gold fragments. In the case of AuPEt3Cl, binding was accompanied by the loss of the chloride ligand, while for [Au(S2O3)2]3- the mass spectral data indicated binding of Au(S2O3) groups. Experiments performed using HSA with Cys34 blocked by reaction with iodoacetamide were consistent with reaction of both gold compounds with this amino acid. Separate blocking experiments using diethylpyrocarbonate and AuPEt3Cl also provided evidence for histidine residues acting as lower-affinity binding sites for this gold compound. ESI mass spectra of solutions containing [Au(S2O3)2]3- or [Au(CN)2]-, and HSA, provided evidence for the formation of protein complexes in which intact gold molecules were non-covalently bound. In the case of [Au(S2O3)2]3-, these non-covalent complexes proved to be transitory in nature. However, for [Au(CN)2]- a non-covalent complex containing a single gold molecule bound to HSA was found to be stable, and constituted the main adduct formed in solutions containing low-to-medium Au-to-HSA ratios. Evidence was also obtained for the formation of a covalent adduct in which a single Au(CN) moiety was bonded to Cys34 of the protein. AuPEt3Cl reacted to a much lower extent with HSA that had Cys34 modified by formation of a disulfide bond to added cysteine, than with unmodified HSA. This suggests that the extent of modification of the protein in vivo may have an important influence on the transport and bioavailability of gold antiarthritic drugs.

Synthesis, Structural Characterization, and Theoretical Studies of Gold(I) and Gold(I)−Gold(III) Thiolate Complexes: Quenching of Gold(I) Thiolate Luminescence

The gold(I) thiolate complexes [Au(2-SC6H4NH2)(PPh3)] (1), [PPN][Au(2-SC6H4NH2)2] (2) (PPN = PPh3=N=PPh3), and [{Au(2-SC6H4NH2)}2(mu-dppm)] (3) (dppm = PPh2CH2PPh2) have been prepared by reaction of acetylacetonato gold(I) precursors with 2-aminobenzenethiol in the appropriate molar ratio. All products are intensely photoluminescent at 77 K. The molecular structure of the dinuclear derivative 3 displays a gold-gold intramolecular contact of 3.1346(4) A. Further reaction with the organometallic gold(III) complex [Au(C6F5)3(tht)] affords dinuclear or tetranuclear mixed gold(I)-gold(III) derivatives with a thiolate bridge, namely, [(AuPPh3){Au(C6F5)3}(mu2-2-SC6H4NH2)] (4) and [(C6F5)3Au(mu2-2-SC6H4NH2)(AudppmAu)(mu2-2-SC(6)H4NH2)Au(C6F5)3] (5). X-ray diffraction studies of the latter show a shortening of the intramolecular gold(I)-gold(I) contact [2.9353(7) or 2.9332(7) A for a second independent molecule], and short gold(I)-gold(III) distances of 3.2812(7) and 3.3822(7) A [or 3.2923(7) and 3.4052(7) A] are also displayed. Despite the gold-gold interactions, the mixed derivatives are nonemissive compounds. Therefore, the complexes were studied by DFT methods. The HOMOs and LUMOs for gold(I) derivatives 1 and 3 are mainly centered on the thiolate and phosphine (or the second thiolate for complex 2), respectively, with some gold contributions, whereas the LUMO for derivative 4 is more centered on the gold(III) fragment. TD-DFT results show a good agreement with the experimental UV-vis absorption and excitation spectra. The excitations can be assigned as a S --> Au-P charge transfer with some mixture of LLCT for derivative 1, an LLCT mixed with ILCT for derivative 2, and a S --> Au...Au-P charge transfer with LLCT and MC for derivative 3. An LMCT (thiolate --> Au(III) mixed with thiolate --> Au-P) excitation was found for derivative 4. The differing nature of the excited states [participation of the gold(III) fragment and the small contribution of sulfur] is proposed to be responsible for quenching the luminescence.

A two-stage process of native palladium formation at low temperatures: evidence from a palladian gold nugget (Gongo Soco iron ore mine, Minas Gerais, Brazil)

AbstractNative palladium is rare and occurs in oxidizing environments (hematite stability field) and consistently has very low contents of other metals. On the other hand, gold may contain significant amounts of alloyed palladium. A nugget of palladian gold, obtained from a specularite-rich auriferous vein (‘jacutinga’) of the Gongo Soco iron ore mine, Quadrilátero Ferrífero, Minas Gerais, allows the definition of a paragenetic sequence of native palladium formation. The cm-sized nugget is brecciated and consists of fragments of palladian gold [Au0.79Pd0.09Cu0.07Ag0.04Hg0.01] with inclusions of isomertieite [Pd11Sb2As2], cemented by kaolinite-hematite-palladian gold infill. The isomertieite inclusions are preferentially fractured and display various degrees of alteration to a Pd-O phase. Native palladium occurs as a crystallized component within the Pd-O phase, with microstructural and chemical features suggesting a desiccation process. It is proposed that native palladium forms by (1) oxidation of a pre-existent palladium mineral to a Pd-O phase, and (2) subsequent crystallization of native palladium from the Pd-O phase, by oxygen loss and dehydration. This process operates in a low-temperature hydrothermal or weathering environment and leads to strong fractionation of palladium and gold.

Fast and Reversible Intramolecular Cleavage of an Au−C Bond in the Spiked-Triangular Metal Complexes [Fe3Au(μ4,η2-C⋮CtBu)(CO)9(PR3)] (R = Ph, iPr)

The C−S bond cleavage in the alkynethiolate ligand of the compound Li[Fe3(μ3-SC⋮CtBu)(CO)9] (1a) takes place in its reaction with [AuClPR3] (R = Ph, iPr), affording the complexes [Fe3Au(μ4,η2-C⋮CtBu)(CO)9(PR3)] (R = Ph (3a), iPr (3b)). The gold fragment displays an unexpected bonding mode, and a fast and reversible process of oxidative addition/reductive elimination of the Au−C bond has been observed in solution.

Reactivity of [Re3(μ-H)3(μ3-ampy)(CO)9]-. Preparation of Heteronuclear Re3Au Carbonyl Cluster Complexes Containing Face-Capping and Edge-Bridging Gold Atoms

The reaction of the trirhenium anionic cluster [Re3(μ-H)3(μ3-ampy)(CO)9]- (1; Hampy = 2-amino-6-methylpyridine) with the cationic gold fragment [Au(PPh3)]+ gives the neutral heteronuclear adducts [Re3{μ3-Au(PPh3)}(μ-H)3(μ3-ampy)(CO)9] (2) and [Re3{μ-Au(PPh3)}(μ3-H)(μ-H)2(μ3-ampy)(CO)9] (3). In compound 2, each hydride ligand spans an edge of the Re3 triangle, which is capped by the gold atom, whereas in compound 3, the gold atom spans a Re2 edge, two hydride ligands span the two symmetry-related Re2 edges, and the remaining hydride ligand caps the Re2Au triangle.

High nuclearity clusters of osmium and ruthenium containing the [Au 2(Ph 2PCH 2PPh 2)] 2+ cation; the X-ray structures of [Os 4H 4(CO) 11Au 2(Ph 2PCH 2PPh 2)] and [Ru 10C(CO) 24Au 2(Ph 2PCH 2PPh 2)

Treatment of [Os 4H 4(CO) 11] 2−, [Os 10C(CO) 24] 2− and [Ru 10C(CO) 24] 2− with [Au 2(Ph 2PCH 2PPh 2)Cl 2] in the presence of an excess of TIPF 6, gave [Os 4H 4(CO) 11(Au 2Ph 2PCH 2PPh 2)] 1, [Os 10C(CO) 24(Au 2Ph 2PCH 2PPh 2)] 2 and [Ru 10C(CO) 24(Au 2Ph 2PCH 2PPh 2)] 3, respectively, all of which were obtained in high yield. The structures of the clusters l and 3 have been established by X-ray crystallography, both exhibiting novel coordination modes of the bidentate gold fragments. Cluster 1 contains a tetrahedral Os 4 core with one of the Au atoms of the Au 2(Ph 2PCH 2PPh 2) ligand bridging an edge of the tetrahedron, and the second Au atom coordinated to a third Os atom. In 3 the two Au atoms of the Au 2(Ph 2PCH 2PPh 2) ligand cap two adjacent, vertex sharing, triangular faces of the Ru 10 tetracapped octahedral core.

Nickel and gold in skin lesions of pierced earlobes with contact dermatitis. A study using scanning electron microscopy and x-ray microanalysis.

Cases of contact dermatitis due to nickel and gold especially in pierced earlobes, are increasing in number the world over. However, the presence of these metal fragments has not been demonstrated in the skin lesions. The aim of this study was to demonstrate nickel and gold in contact dermatitis lesions in pierced earlobes. Skin specimens taken from such earlobe lesions were examined using scanning electron microscopy and x-ray microanalysis. The pierced earrings worn when the lesions appeared were examined by the same techniques, and their analysis confirmed. In nickel dermatitis, small, electron-dense fragments were seen in the specimens examined by scanning electron microscopy, and nickel was detected in locations corresponding to these fragments by x-ray microanalysis. In contact dermatitis due to gold, small dense fragments containing gold were observed. It is suggested that small fragments of nickel and gold remain in the skin lesions of pierced earlobes for a long time, even after the studs have been removed, and cause prolonged irritation and various cutaneous reactions.

Beating of monopole modes in nuclear dynamics

Time-dependent Hartree-Fock simulations of the evolution of excited gold fragments have been performed. The observed dynamics appears more complex than the collective expansion picture. The minimum density is often not reached during the first density oscillation because of the beating of several collective compression modes.

Metal core rearrangements in hetero-bimetallic nona-osmium carbonyl clusters; the crystal and molecular structures of [Os 9(CO) 24{Au(PCy 3)} 2] and [Os 9(CO) 23(Au 2DPPE)

The reaction of the nona-osmium cluster dianion [(Ph 3P) 2N] 2[Os 9(CO) 24] with the electrophilic gold reagents “AuPR + 3” and “Au 2L 2+” (where R=Ph ( 2a, 3a), Cy ( 2b, 3b) and L=bis-(diphenylphosphino)methane (DPPM) ( 1a) or 1,2-bis-(diphenyl)ethane (DPPE) ( 1b)) has been studied. The monogold fragment reacts to give both the mono- and di-substituted products [(Ph 3P) 2N][Os 9(CO) 24{Au(PR 3)}] and [Os 9(CO) 24{Au(PR 3)} 2]. The structure of the latter cluster (R=Cy ( 2b)) has been determined by a single crystal X-ray diffraction analysis and a major rearrangement of the metal core geometry was found to have occurred on coordination of the gold fragments. In contrast, reaction with the digold reagent “Au 2L 2+” results in the isolation of only one product of formulation [Os 9(CO) 23(Au 2L)], where coordination of the heteroatom moiety has been accompanied with the loss of a carbonyl ligand. From a single crystal X-ray diffraction analysis (L=DPPE ( 1b)) this compound was shown to have retained its original cluster geometry, with the gold atoms coordinated in close proximity to each other.

Aurophilicity at Sulfur Centers. Synthesis and Reactivity of the Complex [S(Au2dppf)]; Formation of Polynuclear Sulfur-Centered Complexes. Crystal Structures of [S(Au2dppf)]·2CHCl3, [(μ-Au2dppf){S(Au2dppf)}2](OTf)2· 8CHCl3, and [S(AuPPh2Me)2(Au2dppf)](ClO4)2·3CH2Cl2

Treatment of [Au2Cl2(μ-dppf)] (dppf = 1,1‘-bis(diphenylphosphino)ferrocene) with Li2S (molar ratio 1:1) in ethanol gives a yellow solid [S(Au2dppf)] (1). The sulfur atom in complex 1 can coordinate several neutral or cationic gold(I) fragments giving the trinuclear neutral [S{Au(C6F5)}(Au2dppf)] (2) or cationic derivatives [S(AuL)(Au2dppf)]ClO4 [L = CH2PPh3 (3), PPh3 (4), PPh2Me (5)]. A pentanuclear complex [Au{S(Au2dppf)2}]ClO4 (6) is obtained by reaction of 2 equiv of complex 1 with 1 equiv of [Au(tht)2]ClO4, in which the central gold atom is bonded to two sulfur atoms. Treatment of compound 1 with [Au2(OTf)2(μ-dppf)] (OTf = trifluoromethylsulfonate) in a molar ratio 2:1 affords the hexanuclear complex [(μ-Au2dppf){S(Au2dppf)}2](OTf)2 (7), in which two SAu3 units are joined through the dppf ligand. The reaction of 1 with 2 equiv of [Au(OClO3)PR3] leads to the quadruply bridging derivatives [S(AuPR3)2(Au2dppf)](ClO4)2 [PR3 = PPh3 (8), PPh2Me (9)]. Crystal structure determinations were performed for complexes 1, 7, and 9. [S(Au2dppf)] (1) crystallizes in the monoclinic space group P2/n, with a = 12.571(4) Å, b = 10.579(4) Å, c = 15.212(4) Å, β = 107.84(3)°, Z = 2, T = −130 °C. [(μ-Au2dppf){S(Au2dppf)}2](OTf)2 (7) is triclinic, P1̄, with a = 15.177(3), b = 18.408(4), c = 27.894(8) Å, α = 88.83(2), β = 84.46(2), γ = 67.78(2), Z = 2, T = −100 °C. [S(AuPPh2Me)2(Au2dppf)](ClO4)2 (9) is triclinic, P1̄, with a = 13.727(2) Å, b = 15.952(3) Å, c = 17.763(2) Å, α = 71.738(12)°, β = 73.264(14)°, γ = 75.96(2)°, Z = 2, T = −100 °C. All three complexes display short gold(I)−gold(I) interactions.

A Cluster‐Bound Triply‐Bridging Phosphorus Atom Coordinated to Four (Ph3P)Au+ Units: [Fe3(CO)9P{Au(PPh3)}4][BAr4

The seven-coordinate phosphorus atom in the title compound is bound to a slightly distorted square-planar Au4 array (see structure on the right). Despite the fact that the phosphorus atom is donating all but two of its electrons to the Fe3 cluster, it is still able to act as a nucleus for the aggregation of four gold fragments.

Reversible skeletal rearrangement in a carbido carbonyl cluster induced by ligand substitution. Synthesis and crystal structure of the anion [Rh12C2(CO)23(AuPPh3)

The mixed-metal carbido carbonyl cluster anion [Rh12C2(CO)23(AuPPh3)]– has been obtained by reaction of [Rh12C2(CO)24]2– with [Au(PPh3)Cl]. It is an intermediate species in the previously reported reaction producing the two related clusters [Rh10C2(CO)18(AuPPh3)4] and [Rh10C2(CO)20(AuPPh3)4] and reacts with CO regenerating the starting dianion. The molecular structure of the [NEt4]+ salt has been determined by X-ray diffraction analysis [monoclinic, space group P21/n, Z= 4, a= 13.499(2), b= 32.789(3), c= 14.923(3)A, β= 101.26(2)°]. The loss of a CO ligand and the addition of the gold fragment result in major rearrangements in the Rh12C2 cluster yielding an unprecedented layered aggregation in which three fused trigonal prisms (two containing the carbide atoms) are recognizable. The Au(PPh3)+ fragment bridges a Rh4 butterfly-shaped face of the Rh-atom skeleton. Phosphorus-31 NMR spectra at low temperature show that the solution structure is somewhat different with the gold bonded to a RhARhBRhB face. The CO ligands are distributed in such a way as to achieve a regular charge distribution among the metal atoms.