Isomeric Gold Research Articles

Staggered Assembly of a Dimeric Au13 Cluster: Impacts on Coupling of Geometric Isomerism

AbstractThe specific states of aggregation of metal atoms in sub‐nanometer‐sized gold clusters are related to the different quantum confinement volumes of electrons, leading to novel optical and electronic properties. These volumes can be tuned by changing the relative positions of the gold atoms to generate isomers. Studying the isomeric gold core and the electron coupling between the basic units is fundamentally important for nanoelectronic devices and luminescence; however, appropriate cases are lacking. In this study, the structure of the first staggered di‐superatomic Au25‐S was solved using single‐crystal X‐ray diffraction. The optical properties of Au25‐S were studied by comparing with eclipsed Au25‐E. From Au25‐E to Au25‐S, changes in the electronic structures occurred, resulting in significantly different optical absorptions originating from the coupling between the two Au13 modules. Au25‐S shows a longer electron decay lifetime of 307.7 ps before populating the lowest triplet emissive state, compared to 1.29 ps for Au25‐E. The experimental and theoretical results show that variations in the geometric isomerism lead to distinct photophysical processes owing to isomerism‐dependent electronic coupling. This study offers new insights into the connection between the geometric isomerism of nanosized building blocks and the optical properties of their assemblies, opening new possibilities for constructing function‐specific nanomaterials.

Staggered Assembly of a Dimeric Au13 Cluster: Impacts on Coupling of Geometric Isomerism.

The specific states of aggregation of metal atoms in sub-nanometer-sized gold clusters are related to the different quantum confinement volumes of electrons, leading to novel optical and electronic properties. These volumes can be tuned by changing the relative positions of the gold atoms to generate isomers. Studying the isomeric gold core and the electron coupling between the basic units is fundamentally important for nanoelectronic devices and luminescence; however, appropriate cases are lacking. In this study, the structure of the first staggered di-superatomic Au25 -S was solved using single-crystal X-ray diffraction. The optical properties of Au25 -S were studied by comparing with eclipsed Au25 -E. From Au25 -E to Au25 -S, changes in the electronic structures occurred, resulting in significantly different optical absorptions originating from the coupling between the two Au13 modules. Au25 -S shows a longer electron decay lifetime of 307.7 ps before populating the lowest triplet emissive state, compared to 1.29 ps for Au25 -E. The experimental and theoretical results show that variations in the geometric isomerism lead to distinct photophysical processes owing to isomerism-dependent electronic coupling. This study offers new insights into the connection between the geometric isomerism of nanosized building blocks and the optical properties of their assemblies, opening new possibilities for constructing function-specific nanomaterials.

Gold-Catalyzed Cyclization of Yndiamides with Isoxazoles via α-Imino Gold Fischer Carbenes.

Gold catalysis is an important method for alkyne functionalization. Here we report the gold-catalyzed formal [3+2] aminative cyclization of yndiamides and isoxazoles in a direct synthesis of polysubstituted diaminopyrroles, which are important motifs in drug discovery. Key to this process is the formation, and subsequent cyclization, of an α-imino gold Fischer carbene, which represents a new type of gold carbene intermediate. The reaction proceeds rapidly under mild conditions, with high regioselectivity being achieved by introducing a subtle steric bias between the nitrogen substituents on the yndiamide. DFT calculations revealed that the key to this regioselectivity was the interconversion of isomeric gold keteniminiun ions via a low-barrier π-complex transition state, which establishes a Curtin-Hammett scenario for isoxazole addition. By using benzisoxazoles as substrates, the reaction outcome could be switched to a formal [5+2] cyclization, leading to 1,4-oxazepines.

Isomerization in Alkynyl-Protected Gold Nanoclusters.

We report the controlled synthesis and structures of two isomeric gold nanoclusters, whose compositions are determined to be Au23(C≡CBut)15 (denoted as Au23-1 and Au23-2) by single-crystal X-ray diffraction and matrix-assisted laser desorption ionization time-of-flight mass spectrometry. This is the first time isomerism is discovered in alkynyl-protected gold nanoclusters. The metal-to-ligand ratios in these two clusters are different from known Aun(SR)m systems and have not been observed in the Aux(C≡CPh)y family. This pair of isomers exhibits different optical properties, although they have similar structures and identical components. For both Au23 clusters,time-dependent density functional theory calculations revealed the frontier orbitals highest occupied molecular orbital (HOMO)-1, HOMO, and lowest unoccupied molecular orbital (LUMO) are mainly constructed from the Au15 kernel and V-shaped alkynyl-gold motifs. The HOMO → LUMO transition of Au23-1 is optically forbidden, whereas it is allowed in Au23-2. It is also found that Au23-2 cluster can be transformed to Au23-1 spontaneously under ambient conditions. This work offers further insight into the synthesis and isomerism of all-alkynyl-protected gold nanoclusters and will stimulate more investigation of isomeric metal nanoclusters.

Chemisorption Activity of Mercury(II) Cyclopentamethylenedithiocarbamate: Synthesis, Structure, and Thermal Behavior of the [Hg2{S2CN(CH2)5}4] and [Au3{S2CN(CH2)5}6][Au{S2CN(CH2)5}2][Hg2Cl6]2 Complexes

The dinuclear complex mercury(II) cyclopentamethylenedithiocarbamate (piperidine-1-carbodithioate) [Hg2{S2CN(CH2)5}4] was synthesized and its chemisorption activity toward a solution of AuCl3 in 2 M HCl was studied. The chemisorption of gold from the solution forms an ionic gold(III)‒mercury(II) dithiocarbamato-chlorido complex comprising three isomeric gold cations and an unsymmetrical hexachlorodimercurate anion. The structural organization and thermal behavior of the resulting compounds was studied.

Multiple isomerization of structural units in ion-polymeric heteronuclear gold(III)–zinc(II) complex ([Au{S2CN(C4H9)2}2]2[ZnCl4])n: Chemisorption-based synthesis, supramolecular structure (self-organization of long-period cation–cationic polymer chains), and thermal behavior

Chemisorption of gold(III) from solutions in 2 M HCl with freshly precipitated binuclear zinc dithiocarbamate [Zn2{S2CN(C4H9)2}4] resulted in the formation of a polymeric heteronuclear gold(III)–zinc(II) dithiocarbamato-chlorido complex ([Au{S2CN(C4H9)2}2]2[ZnCl4]) n (I), which was characterized by MAS 13C NMR, X-ray diffraction (CIF file CCDC no. 1526616), and simultaneous thermal analysis. Compound I isolated on a preparative scale was found to have a highly intricate supramolecular structure composed of 13 centrosymmetric and non-centrosymmetric isomeric complex cations, [Au{S2CN(C4H9)2}2]+, with 24 structurally non-equivalent BuDtc ligands, and six isomeric [ZnCl4]2– anions. The isomeric gold(III) cations perform different structural functions. Four and six cations are involved in the formation of two sorts of long-period cation–cationic chains (via pair non-valence secondary Au···S bonds): (···A···B···C···D···C···B···) n and (···F···G···H···I···J···K···) n . The discrete E, L, and M cations and the [ZnCl4]2– complex anions are located alongside of the polymer chains and do not take part in the secondary interactions. According to simultaneous thermal analysis, thermolysis of I includes destruction of the dithiocarbamate moiety with reduction of gold to the metal in the cation and liberation of zinc chloride with partial conversion to ZnS in the anion.

A new polymorphic modification and chemisorption activity of mercury(II) N,N-di-iso-propyldithiocarbamate: Synthesis and characterisation of the heteronuclear double complex of ([Au{S2CN(iso-C3H7)2}2]2[Hg2Cl6]·OC(CH3)2)n

A new crystalline modification (γ-form, 1) of the mercury(II) N,N-di-iso-propyldithiocarbamate (Hg-iso-PDtc) has been identified and structurally characterised using single-crystal X-ray diffraction analysis. The crystal structure of 1 is presented by centrosymmetric binuclear molecules of [Hg2{S2CN(iso-C3H7)2}4], in which the mercury atoms are interconnected by two tridentate bridging iso-PDtc ligands. The chemisorption activity of the freshly precipitated Hg-iso-PDtc was tested with respect to gold(III) in a 2M HCl solution. The novel heteronuclear gold(III)–mercury(II) double complex was found to be the sole gold-containing product of the chemisorption. The isolated compound was crystallised as a solvated form, ([Au{S2CN(iso-C3H7)2}2]2[Hg2Cl6]·OC(CH3)2)n (2). It was revealed that compound 2 adopts a polymeric structure comprising two types (‘A’ and ‘B’) of isomeric gold(III) cations [Au{S2CN(iso-C3H7)2}2]+ and centrosymmetric binuclear mercury(II) anions [Hg2Cl6]2–. The supramolecular self-organisation of 2 occurs due to the relatively weak Au···S secondary interactions between neighbouring isomeric [Au{S2CN(iso-C3H7)2}2]+ cations resulting in the formation of linear cation-cationic chains of (⋯‘A’⋯‘B’⋯‘A’⋯‘B’⋯)n. The thermal behaviour of polycrystalline samples of Hg-iso-PDtc and 2 was studied by simultaneous thermal analysis (STA). It was shown that thermal decomposition is accompanied by the formation of HgS (for the original mercury(II) complex) or quantitative reduction of gold(III) to elemental gold and formation of HgCl2 along with its partial transformation to HgS (for 2).

Chemisorption binding of gold(III) from solutions with bismuth dipropyldithiocarbamate: Supramolecular self-assembly (role of the secondary Au…S and aurophilic interactions) and thermal behavior of the solvated heteropolynuclear ionic type complex ([Au{S2CN(C3H7)2}2]3[Bi2Cl9] • 0.5CO(CH3)2 • 0.5HCl) n

The reaction of binuclear bismuth(III) N,N-dipropyldithiocarbamate [Bi2{S2CN(C3H7)2}6] with a solution of AuCl3 in 2 M HCl was studied. Crystallization of the heterogeneous reaction products from an acetone solution afforded the polymeric solvated heteropolynuclear gold(III)–bismuth complex, ([Au{S2CN(C3H7)2}2]3[Bi2Cl9] · 1/2CO(CH3)2 · 1/2HCl)n (I). According to X-ray diffraction data (CIF file CCDC no. 1050766), the structure of I comprises four isomeric [Au{S2CN(C3H7)2}2]+ cations in 1: 1: 2: 2 ratio, namely: cation “A” with the Au(1) atom, cation “B” with the Au(2) atom, cation “C” with the Au(3) atom, and cation “D” with the Au(4) atom, and the discrete binuclear [Bi2Cl9]3– anions. The isomeric gold(III) complex cations are involved in the construction of two types of cationic triads, [“C”···“A”···“C”] and [“D”···“B”···“D”], through secondary bonds and short Au···S contacts. The cation types differ by both the nature of binding and the Au–Au distances. The weak aurophilic binding between the cationic triads (Au···Au 3.5416(2) A) gives rise to zigzag-like polymeric chains (···[“C”···“A”···“C”]···[“D”···“B”···“D”]···)n extended along the y axis. In turn, the [Bi2Cl9]3– anions located on one side of polymer chains are held by the secondary Cl···S bonds. The outer-sphere CO(CH3)2 and HCl solvate molecules joined by hydrogen bonds are located in the space between bismuth anions. The thermal behavior of I was studied by simultaneous thermal analysis. The thermal destruction of the complex includes desolvation and thermolysis of the dithiocarbamate moiety and [Bi2Cl9]3– with liberation of gold metal and bismuth chloride (which is subsequently evaporated) and partial formation of Bi2S3. In the temperature range of 712–828°C, bismuth sulfide is oxidized to (BiO)2SO4, which decomposes above 828°C to give Bi2O3. Bismuth(III) oxide and reduced gold are the final products of thermal transformations.

Phosphanchalkogenide und ihre Metallkomplexe. II. Komplexe einiger Gold(I)-Halogenide mit Diphosphanmonochalkogeniden [1] / Phosphane Chalcogenides and their Metal Complexes. II. Gold(I) Halide Complexes of some Diphosphane Monochalcogenides

We report the crystal structures of 19 gold(I) complexes with diphosphane monochalcogenide ligands, general formula (PP)EAuHal (PP = diphosphane, E = chalcogen, Hal = halogen). For PP = bis(diphenylphosphano)methane (dppm): 1, dppmOAuCl as its diisopropyl ether solvate; 2, dppmOAuI as its dichloromethane solvate; 3, dppmSAuCl as its dichloromethane hemisolvate; 4, dppmSAuI; 5, dppmSeAuBr as a 1:1 adduct with dppmSe2; 6, dppmSeAuI. Compound 3 is isotypic to the known structure of dppmSeAuCl. Most of the structures have an E-P…P-Au torsion angle close to zero, which, especially for the larger E atoms, facilitates a close intramolecular approach of E and Au. The packing of 1-3 involves hydrogen bonds from the methylene hydrogens. For PP = 1,2-bis(diphenylphosphano)ethane (dppe): 7, dppeOAuBr and 8, dppeOAuI, both as their hemihydrates; 9, dppeSAuBr; 10, dppeSAuI. All four compounds crystallise with two independent molecules of the gold complex, between which short Au…Au contacts are observed; the molecules of 7 and 8 are further linked by hydrogen bond systems […P=O…H-O-H…O=P…]. Compounds 7 and 8 form an isotypic series with their known chloride analogue, as do 9 and 10. For PP = 1,2- bis(diphenylphosphano)benzene (dppbz): 11, dppbzOAuCl; 12, dppbzOAuBr; 13, dppbzSAuBr; 14, dppbzSAuI, 16, dppbzSeAuBr and 17, dppbzSeAuI, all as their isotypic dichloromethane disolvates; 15, dppbzSeAuCl (isotypic to 13). The absolute E-P…P-Au torsion angles are all in the range 50 - 70°; short intramolecular E…Au contacts are observed. The packing of 11-17 shows few notable short contacts. For PP = cis-1,2-bis(diphenylphosphano)ethene (cisdppen): 18, cisdppenSAuCl; 19, cisdppenSAuBr. Both compounds crystallise with two independent molecules, and in both cases the molecules display considerable differences in configuration. The packing of 18 involves short H…Cl and that of 19 short H…S contacts. For PP = 1,8-bis(diphenylphosphano)naphthalene (dppn), an inversion-symmetric gold(III) complex (dppnSeAu)2Cl2 20, with a central four-membered ring Au2Se2, was obtained instead of the expected isomeric gold(I) derivative by formal insertion of gold into a P-Se bond; it crystallised as a deuterochloroform hexasolvate.

Synthesis and interconversions of digold(i), tetragold(i), digold(ii), gold(i)–gold(iii) and digold(iii) complexes of fluorine-substituted aryl carbanions

Treatment of [AuXL] (X = Br, L = AsPh(3); X = Cl, L = tht) with the lithium or trimethyltin derivatives of the carbanions [2-C6F4PPh2]- and [C6H3-n-F-2-PPh2]- (n = 5, 6) gives digold(I) complexes [Au2(mu-carbanion)2] (carbanion = 2-C6F4PPh2 2, C6H3-5-F-2-PPh2 3, C6H3-6-F-2-PPh2 4) which, like their 2-C6H4PPh2 counterpart, undergo oxidative addition with halogens X2 (X = Cl, Br, I) to give the corresponding, metal-metal bonded digold(II) complexes [Au2X2(mu-carbanion)2] (carbanion = 2-C6F4PPh2, X = Cl 5, Br 8, I 11; carbanion = C6H3-5-F-2-PPh2, X = Cl 6, Br 9, I 12; carbanion = C6H3-6-F-2-PPh2, X = Cl 7, Br 10, I 13). In the case of 2-C6F4PPh2 and C6H3-6-F-2-PPh2, the dihalodigold(II) complexes rearrange on heating to isomeric gold(I)-gold(III) complexes [XAu(I)(mu-P,C-carbanion)(kappa2-P,C-carbanion)Au(III)X] (carbanion = 2-C6F4PPh2, X = Cl 25, Br 26, I 27; carbanion = C6H3-6-F-2-PPh2, X = Cl 28, Br 29, I 30), in which one of the carbanions chelates to the gold(III) atom. This isomerisation is similar to, but occurs more slowly than, that in the corresponding C6H3-6-Me-2-PPh2 system. The Au2X2 complexes 6, 9 and 12, on the other hand, rearrange on heating via C-C coupling to give digold(I) complexes of the corresponding 2,2'-biphenyldiylbis(diphenylphosphine), [Au2X2(2,2'-Ph2P-5-F-C6H3C6H3-5-F-PPh2)] (X = Cl 32, Br 33, I 34), this behaviour resembling that of the 2-C6H4PPh2 and C6H3-5-Me-2-PPh2 systems. Since the C-C coupling probably occurs via undetected gold(I)-gold(III) intermediates, the presence of a 6-fluoro substituent is evidently sufficient to suppress the reductive eliminations, possibly because of an electronic effect that strengthens the gold(III)-aryl bond. Anation of 5 or 8 gives the bis(oxyanion)digold(II) complexes [Au2Y2(mu-2-C6F4PPh2)2] (Y = OAc 14, ONO2 15, OBz 16, O2CCF3 17 and OTf 20), which do not isomerise to the corresponding gold(I)-gold(III) complexes [YAu(mu-2-C6F4PPh2)(kappa2-2-C6F4PPh2)AuY] on heating, though the latter [Y = OAc 35, ONO2 36, OBz 37, O2CCF3 38] can be made by anation of 25-27. Reaction of the bis(benzoato)digold(II) complex 16 with dimethylzinc gives a dimethyl gold(I)-gold(III) complex, [Au(I)(mu-2-C6F4PPh2)2Au(III)(CH3)2] 19, in which both 2-C6F4PPh2 groups are bridging. In contrast, the corresponding reaction of 16 with C6F5Li gives a digold(II) complex [Au(II)2(C6F5)2(mu-2-C6F4PPh2)2] 18, which on heating isomerises to a gold(I)-gold(III) complex, [(C6F5)Au(I)(mu-2-C6F4PPh2)(kappa2-2-C6F4PPh2)Au(III)(C6F5)] 31, analogous to 25-27. The bis(triflato)digold(II) complex 20 is reduced by methanol or cyclohexanol in CH2Cl2 to a tetranuclear gold(I) complex [Au4(mu-2-C6F4PPh2)4] 21 in which the four carbanions bridge a square array of metal atoms, as shown by a single-crystal X-ray diffraction study. The corresponding tetramers [Au4(mu-C6H3-n-F-2-PPh2)4] (n = 5 22, 6 23) are formed as minor by-products in the preparation of dimers 3 and 4; the tetramers do not interconvert readily with, and are not in equilibrium with, the corresponding dimers 2-4. Addition of an excess of chlorine or bromine (X2) to the digold(II) complexes 5 and 8, and to their gold(I)-gold(III) isomers 25 and 26, gives isomeric digold(III) complexes [Au2X4(mu-2-C6F4PPh2)2] (X = Cl 39, Br 40) and [X3Au(mu-2-C6F4PPh2)AuX(kappa2-2-C6F4PPh2)] (X = Cl 41, Br 42), respectively. The structures of the digold(I) complexes 2, 4 and 32, the digold(II) complexes 5-11 and 14-18, the gold(I)-gold(III) complexes 19, 25, 35 and 38, the tetragold(I) complexes 21 and 22, and the digold(III) complexes 41 and 42, have been determined by single-crystal X-ray diffraction. In the digold(II) (5d9-5d9) series, there is a systematic lengthening, and presumably weakening, of the Au-Au distance in the range 2.5012(4)-2.5885(2) A with increasing trans-influence of the axial ligand, in the order X = ONO2 < O2CCF3 < OBz < Cl < Br < I < C6F5. The strength of the Au-Au interaction is probably the main factor that determines whether the digold(II) compounds isomerise to gold(I)-gold(III). The gold-gold separations in the digold(I) and gold(I)-gold(III) complexes are in the range 2.8-3.6 A suggestive of aurophilic interactions, but these are probably absent in the digold(III) compounds (Au...Au separation ca. 5.8 A). Attempted recrystallisation of complex 10 gave a trinuclear gold(II)-gold(II)-gold(I) complex, [Au3Br2(mu-C6H3-6-F-2-PPh2)3] 24, which consists of the expected digold(II) framework in which one of the axial bromide ligands has been replaced by a sigma-carbon bonded (C6H3-6-F-2-PPh2)Au(I)Br fragment.

Synthesis, crystal structure and antimicrobial activities of two isomeric gold(I) complexes with nitrogen-containing heterocycle and triphenylphosphine ligands, [Au(L)(PPh 3)] (HL=pyrazole and imidazole)

Two isomeric gold(I)–triphenylphosphine complexes with nitrogen-containing heterocycles, [Au(L)(PPh 3)] (HL=pyrazole ( 1), imidazole ( 2)), were isolated as colorless cubic crystals for 1 and colorless plate crystals for 2, respectively. The crystal structures of 1 and 2 were determined by single-crystal X-ray diffraction. These complexes were also fully characterized by complete elemental analyses, thermogravimetric/differential thermal analyses (TG/DTA) and FT-IR in the solid state and by solution NMR ( 31P, 1H and 13C) spectroscopy and molecular weight measurements in acetone solution. These complexes consisted of a monomeric 2-coordinate AuNP core both in the solid state and in solution. The molecular structures of 1 and 2 were compared with those of related gold(I) complexes, [Au(1,2,3-triz)(PPh 3)] ( 3, Htriz=triazole), [Au(1,2,4-triz)(PPh 3)] 2 ( 4) as a dimer through a gold(I)–gold(I) bond in the solid state, and [Au(tetz)(PPh 3)] ( 5, Htetz=tetrazole). Selective and effective antimicrobial activities against two Gram-positive bacteria ( B. subtilis, S. aureus) and modest activities against one yeast ( C. albicans) found in these gold(I) complexes 1– 4 are noteworthy, in contrast to poor activities observed in the corresponding silver(I) complexes.