Luminescent di- and polynuclear organometallic gold(I)-metal (Au2, {Au2Ag}n and {Au2Cu}n) compounds containing bidentate phosphanes as active antimicrobial agents

The reaction of new dinuclear gold(I) organometallic complexes containing mesityl ligands and bridging bidentate phosphanes [Au(2)(mes)(2)(μ-LL)] (LL=dppe: 1,2-bis(diphenylphosphano)ethane 1a, and water-soluble dppy: 1,2-bis(di-3-pyridylphosphano)ethane 1b) with Ag(+) and Cu(+) lead to the formation of a family of heterometallic clusters with mesityl bridging ligands of the general formula [Au(2)M(μ-mes)(2) (μ-LL)][A] (M=Ag, A=ClO(4)(-), LL=dppe 2a, dppy 2b; M=Ag, A=SO(3)CF(3)(-), LL=dppe 3a, dppy 3b; M=Cu, A=PF(6)(-), LL=dppe 4a, dppy 4b). The new compounds were characterized by different spectroscopic techniques and mass spectrometry The crystal structures of [Au(2)(mes)(2)(μ-dppy)] (1b) and [Au(2)Ag(μ-mes)(2)(μ-dppe)][SO(3)CF(3)] (3a) were determined by a single-crystal X-ray diffraction study. 3a in solid state is not a cyclic trinuclear Au(2)Ag derivative but it gives an open polymeric structure instead, with the {Au(2)(μ-dppe)} fragments "linked" by {Ag(μ-mes)(2)} units. The very short distances of 2.7559(6)?? (Au-Ag) and 2.9229(8)?? (Au-Au) are indicative of gold-silver (metallophilic) and aurophilic interactions. A systematic study of their luminescence properties revealed that all compounds are brightly luminescent in solid state, at room temperature (RT) and at 77?K, or in frozen DMSO solutions with lifetimes in the microsecond range and probably due to the self-aggregation of [Au(2)M(μ-mes)(2)(μ-LL)](+) units (M=Ag or Cu; LL=dppe or dppy) into an extended chain structure, through Au-Au and/or Au-M metallophilic interactions, as that observed for 3a. In solid state the heterometallic Au(2)M complexes with dppe (2a-4a) show a shift of emission maxima (from ca. 430 to the range of 520-540?nm) as compared to the parent dinuclear organometallic product 1a while the complexes with dppy (2b-4b) display a more moderate shift (505 for 1b to a max of 563?nm for 4b). More importantly, compound [Au(2)Ag(μ-mes)(2)(μ-dppy)]ClO(4) (2b) resulted luminescent in diluted DMSO solution at room temperature. Previously reported compound [Au(2)Cl(2)(μ-LL)] (LL dppy 5b) was also studied for comparative purposes. The antimicrobial activity of 1-5 and Ag[A] (A=ClO(4)(-), SO(3)CF(3)(-)) against gram-positive and gram-negative bacteria and yeast was evaluated. Most tested compounds displayed moderate to high antibacterial activity while heteronuclear Au(2)M derivatives with dppe (2a-4a) were the more active (minimum inhibitory concentration 10 to 1?μg?mL(-1)). Compounds containing silver were ten times more active to gram-negative bacteria than the parent dinuclear compound 1a or silver salts. Au(2)Ag compounds with dppy (2b, 3b) were also potent against fungi.     

Synthesis, Chemical Characterization, and Molecular Structure of Au8{Fe(CO)4}4(dppe)2 and Au6Cu2{Fe(CO)4}4(dppe)2

The new Au₈{Fe(CO)₄}₄(P^P)₂ and Au₆Cu₂{Fe(CO)₄}₄(P^P)₂ (P^P=dppm, dppe) neutral cluster compounds were isolated in good yields by condensation of the [Au₃{Fe(CO)₄}₂(P^P)]^- anions with Au(SEt₂)Cl and CuCl, respectively, and have been characterized by IR, NMR and microanalyses. The molecular structures of Au₈{Fe(CO)₄}₄(dppe)₂ and Au₆Cu₂{Fe(CO)₄}₄(dppe)₂ have been determined by X-ray diffraction studies. Both molecules adopt a stereogeometry of the heavy atoms consisting of a triangulated and corrugated ribbon twisted around the elongation direction. Contrary to the expectations the latter displays the two copper atoms in the sites of highest connectivity. This implies that site exchange between copper and gold occurs during the synthesis.     

Bimetallic Au2Cu6 Nanoclusters: Strong Luminescence Induced by the Aggregation of Copper(I) Complexes with Gold(0) Species

The concept of aggregation‐induced emission (AIE) has been exploited to render non‐luminescent Cu^ISR complexes strongly luminescent. The Cu^ISR complexes underwent controlled aggregation with Au⁰. Unlike previous AIE methods, our strategy does not require insoluble solutions or cations. X‐ray crystallography validated the structure of this highly fluorescent nanocluster: Six thiolated Cu atoms are aggregated by two Au atoms (Au₂Cu₆ nanoclusters). The quantum yield of this nanocluster is 11.7 %. DFT calculations imply that the fluorescence originates from ligand (aryl groups on the phosphine) to metal (Cu^I) charge transfer (LMCT). Furthermore, the aggregation is affected by the restriction of intramolecular rotation (RIR), and the high rigidity of the outer ligands enhances the fluorescence of the Au₂Cu₆ nanoclusters. This study thus presents a novel strategy for enhancing the luminescence of metal nanoclusters (by the aggregation of active metal complexes with inert metal atoms), and also provides fundamental insights into the controllable synthesis of highly luminescent metal nanoclusters.     

Oxidation‐induced nanostructures on Cu{100}, Cu(Ag) and Ag/Cu{100} studied by photoelectron spectroscopy

Initial surface oxidation and nanoscale morphology on Cu{100}, Cu(Ag) and Ag/Cu{100} have been investigated in situ by X‐ray photoelectron spectroscopy (XPS), X‐ray induced Auger electron spectroscopy (XAES) and the inelastic electron background analysis as a function of oxygen exposure at 3.7 × 10^?2 and 213 mbar pressures at a surface temperature of 373 K. Relative Cu₂O concentrations have been quantified by analysis of the peak shape of the XAES Cu LMM transition. The surface morphology of Cu₂O islands and the Ag layer has been characterized by inelastic electron background analysis of XAES O KLL and Ag 3d transitions. Oxygen‐induced segregation of Cu, as well as the subsequent Cu₂O island formation on Cu(Ag) and Ag/Cu{100} surfaces, has been investigated quantitatively. Our results indicate that Ag has a clear inhibitive effect on the initial oxidation and Cu₂O island formation on Cu(Ag) and Ag/Cu{100} surfaces. The Cu₂O islands are also observed to remain highly strained on Ag/Cu{100} even at higher O₂ exposures. The results suggest that strained Cu₂O islands eventually penetrate through the buried Ag layer, and in conjunction with segregating Cu atoms enable the oxidation to proceed at a similar rate to or even faster than on the unalloyed Cu surface. Copyright © 2007 John Wiley & Sons, Ltd.     

An Atomically Precise Au10Ag2 Nanocluster with Red–Near‐IR Dual Emission

A red–near‐IR dual‐emissive nanocluster with the composition [Au₁₀Ag₂(2‐py?C≡C)₃(dppy)₆](BF₄)₅ ( 1 ; 2‐py?C≡C is 2‐pyridylethynyl, dppy=2‐pyridyldiphenylphosphine) has been synthesized. Single‐crystal X‐ray structural analysis reveals that 1 has a trigonal bipyramidal Au₁₀Ag₂ core that contains a planar Au₄(2‐py?C≡C)₃ unit sandwiched by two Au₃Ag(dppy)₃ motifs. Cluster 1 shows intense red–NIR dual emission in solution. The visible emission originates from metal‐to‐ligand charge transfer (MLCT) from silver atoms to phosphine ligands in the Au₃Ag(dppy)₃ motifs, and the intense NIR emission is associated with the participation of 2‐pyridylethynyl in the frontier orbitals of the cluster, which is confirmed by a time‐dependent density functional theory (TD‐DFT) calculation.     

A Controlled Route to a Luminescent 3 d10–5 d10 Sulfido Cluster Containing Unique AuCu2(μ3‐S) Motifs

The first examples of gold(I) trimethylsilylchalcogenolate complexes were synthesized and their reactivity showcased in the preparation of a novel gold–copper–sulfur cluster [Au₄Cu₄S₄(dppm)₂] (dppm=bis(diphenylphosphino)methane). The unprecedented structural chemistry of this compound gives rise to interesting optoelectronic properties, including long‐lived orange luminescence in the solid state. Through time‐dependent density functional theory calculations, this emission is shown to originate from ligand‐to‐metal charge transfer facilitated by Au???Cu metallophilic bonding.     

A Unique Au–Ag–Au Triangular Motif in a Trimetallic Halonium Dication: Silver Incorporation in a Gold(I) Catalyst

As a result of explorations into the solution chemistry of silver/gold mixtures, a unique diphosphine trimetallic chloronium dication was discovered that incorporates silver–arene chelation and a triangular mixed gold/silver core in the solid state. Notably, it was isolated from a Celite prefiltered solution initially thought to be silver‐free. The crystal structure also incorporates the coordination to silver of one fluorine atom of one SbF₆^? counterion. The structure was compared to two new, but well‐precedented, phosphine digold chloride cations. DFT calculations supported significant silver–halide and silver–arene interactions in the mixed gold/silver complex and metallophilic interactions in all three complexes. Comparison of computed data revealed that the ωB97X‐D functional, which has a long‐range corrected hybrid with atom–atom dispersion corrections, gave a better fit to the experimental data compared with the PBE0 functional, which has previously failed to capture aurophilic interactions. Preliminary studies support the presence of the mixed gold/silver structure in solution.     

Discrete Silver(I)‐Palladium(II)‐Oxo Nanoclusters, {Ag4Pd13} and {Ag5Pd15}, and the Role of Metal–Metal Bonding Induced by Cation Confinement

We introduce the class of discrete silver(I)‐palladium(II)‐oxo nanoclusters with the preparation of {Ag₄Pd₁₃} and {Ag₅Pd₁₅}. Both polyanions represent the first examples of noble metal‐capped polyoxo‐noble‐metalates in a fully inorganic assembly, featuring an unprecedented host–guest mode containing hetero‐ and homometallic Ag–Pd and Ag–Ag bonding interactions. Comprehensive theoretical calculations suggest that the Ag–Pd metallic bonds originate partially from surface confinement of Ag^I guest ions onto the anionic polyoxopalladate host that is induced by strong electrostatic forces. This work opens the field of fully inorganic silver‐palladium‐oxo nanoclusters, which can be considered as discrete mixed noble metal precursors for the formation of monodisperse core–shell nanoparticles, with high relevance for catalysis.     

ChemInform Abstract: Quantitative Analysis of Electron Correlation in M2Po (M: Cu,Ag, Au) Systems

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Cyclic Triradicals Composed of Iminonitroxide–Gold(I) with Intramolecular Ferromagnetic Interactions

A triangular gold(iminonitroxide‐2‐ide) trimer complex ( 5 ) was prepared and investigated to determine its magnetic properties. The results showed that the metalloid triradical is highly stable, even in solution under aerated conditions. The intramolecular exchange interaction of 5 was found to be positive (J_intra/k_B≈+29 K), thus showing that 5 is in a quartet ground state. In addition, a silver sandwich complex ( 5 ‐Ag⁺‐ 5 ) was prepared and its electronic and magnetic properties were also clarified.     

Tunable Trimers: Using Temperature and Pressure to Control Luminescent Emission in Gold(I) Pyrazolate‐Based Trimers

A systematic investigation into the relationship between the solid‐state luminescence and the intermolecular Au???Au interactions in a series of pyrazolate‐based gold(I) trimers; tris(μ₂‐pyrazolato‐N,N′)‐tri‐gold(I) ( 1 ), tris(μ₂‐3,4,5‐ trimethylpyrazolato‐N,N′)‐tri‐gold(I) ( 2 ), tris(μ₂‐3‐methyl‐5‐phenylpyrazolato‐N,N′)‐tri‐gold(I) ( 3 ) and tris(μ₂‐3,5‐diphenylpyrazolato‐N,N′)‐tri‐gold(I) ( 4 ) has been carried out using variable temperature and high pressure X‐ray crystallography, solid‐state emission spectroscopy, Raman spectroscopy and computational techniques. Single‐crystal X‐ray studies show that there is a significant reduction in the intertrimer Au???Au distances both with decreasing temperature and increasing pressure. In the four complexes, the reduction in temperature from 293 to 100 K is accompanied by a reduction in the shortest intermolecular Au???Au contacts of between 0.04 and 0.08 Å. The solid‐state luminescent emission spectra of 1 and 2 display a red shift with decreasing temperature or increasing pressure. Compound 3 does not emit under ambient conditions but displays increasingly red‐shifted luminescence upon cooling or compression. Compound 4 remains emissionless, consistent with the absence of intermolecular Au???Au interactions. The largest pressure induced shift in emission is observed in 2 with a red shift of approximately 630 cm^?1 per GPa between ambient and 3.80 GPa. The shifts in all the complexes can be correlated with changes in Au???Au distance observed by diffraction.     

Neue arsinidenverbrückte Mehrkern-Clusterkomplexe des Ag und Au. Die Kristallstrukturen von [Ag14(AsPh)6Cl2(PR3)8], (PR3 = PEt3, PMenPr2, PnPr3), [M4(As4Ph4)2(PR3)4], (M = Ag,PR3 = PEt3, PnPr3; M = Au,PR3 = PnPr3), [Au10(AsPh)4(PhAsSiMe3)2(PnPr3)6]

New Arsinidene-bridged Multinuclear Cluster Complexes of Ag and Au. The Crystal Structures of [Ag₁₄(AsPh)₆Cl₂(PR₃)₈], (PR₃ = PEt₃, PMeⁿPr₂, PⁿPr₃), [M₄(As₄Ph₄)₂(PR₃)₄], (M = Ag, PR₃ = PEt₃, PⁿPr₃; M = Au, PR₃ = PⁿPr₃), [Au₁₀(AsPh)₄(PhAsSiMe₃)₂(PⁿPr₃)₆] The reaction of AgCl with PhAs(SiMe₃)₂ in presence of tertiary phosphines (PR₃) leads to arsinidene-bridged silver clusters with the composition [Ag₁₄(AsPh)₆Cl₂(PR₃)₈], (PR₃ = PEt₃ 1 , PMeⁿPr₂ 2 , PⁿPr₃ 3 ). Further it is possible to obtain the multinuclear complexes [Ag₄(As₄Ph₄)₂(PR₃)₄], (PR₃ = PEt₃ 4 , PMeⁿPr₂ 5 ). In analogy to that [PMe₃AuCl] reacts with PhAs(SiMe₃)₂ and PⁿPr₃ to form the compound [Au₄(As₄Ph₄)₂(PⁿPr₃)₄] 6 , which is isostructurell to 4 and 5 . The gold cluster [Au₁₀(AsPh)₄(PhAsSiMe₃)₂(PⁿPr₃)₆] 7 was obtained from the same solution. The structures were characterized by X-ray single crystal structure analysis. (Crystallographic data see “Inhaltsübersicht”)     

Analysis of High and Selective Uptake of CO2 in an Oxamide‐Containing {Cu2(OOCR)4}‐Based Metal–Organic Framework

The porous framework [Cu₂(H₂O)₂L] ? 4 H₂O ? 2 DMA (H₄L=oxalylbis(azanediyl)diisophthalic acid; DMA=N,N‐dimethylacetamide), denoted NOTT‐125, is formed by connection of {Cu₂(RCOO)₄} paddlewheels with the isophthalate linkers in L^4?. A single crystal structure determination reveals that NOTT‐125 crystallises in monoclinic unit cell with a=27.9161(6), b=18.6627(4) and c=32.3643(8) Å, β=112.655(3)°, space group P2₁/c. The structure of this material shows fof topology, which can be viewed as the packing of two types of cages (cage A and cage B) in three‐dimensional space. Cage A is constructed from twelve {Cu₂(OOCR)₄} paddlewheels and six linkers to form an ellipsoid‐shaped cavity approximately 24.0 Å along its long axis and 9.6 Å across its central diameter. Cage B consists of six {Cu₂(OOCR)₄} units and twelve linkers and has a spherical diameter of 12.7 Å taking into account the van der Waals radii of the atoms. NOTT‐125 incorporates oxamide functionality within the pore walls, and this, combined with high porosity in desolvated NOTT‐125a, is responsible for excellent CO₂ uptake (40.1 wt % at 273 K and 1 bar) and selectivity for CO₂ over CH₄ or N₂. Grand canonical Monte Carlo (GCMC) simulations show excellent agreement with the experimental gas isotherm data, and a computational study of the specific interactions and binding energies of both CO₂ and CH₄ with the linkers in NOTT‐125 reveals a set of strong interactions between CO₂ and the oxamide motif that are not possible with a single amide.     

Synthesis and Structure of { (Tab-Tab) [Ag2(μ-Cl)4]·2MeCN}n (Tab = 4-(Trimethylammonio)benzenethiolate)

In the presence of Et4NCl?H2O,reaction of AgCl with TabHPF6 in MeCN afforded the title complex {(Tab-Tab)[Ag2(μ-Cl)4]·2MeCN}n 1.1 crystallizes in the orthorhombic space group Pbcn with a=16.782(3),b=6.8358(14),c=26.194(5) ,V=3004.9(10) 3,Z=8,μ= 1.817 mm-1,Dc=1.711 g/cm3,T=223 K,C11H16AgCl2N2S,Mr=387.10,F(000)=1544,S=1.160,R=0.0528 and wR=0.0896 for 2732 observed reflections with I > 2σ(I).1 contains a 1D linear [Ag2Cl4]n2n-chain coupled with the [Tab-Tab]2+ dications.Intermolecular hydrogen bonding interac-tions between the protons of methyl groups from the Tab-Tab dications and the chlorides result in the formation of a 2D hydrogen-bonded network.     

Reversible Interconversion between Luminescent Isomeric Metal–Organic Frameworks of [Cu4I4(DABCO)2] (DABCO=1,4‐Diazabicyclo[2.2.2]octane)

The metal–organic frameworks (MOF) of cluster [Cu₄I₄(DABCO)₂] (DABCO=1,4‐diazabicyclo[2.2.2]octane) have been prepared and characterized as two different crystalline forms, I and II . Form I is obtained by reaction of DABCO and CuI in aqueous solution or by solvothermal reaction, while form II is obtained by reacting DABCO and CuI in acetonitrile. Their luminescence properties in the solid state have been analyzed at room temperature and at 77 K. MOF II has bright emission with a maximum at 556 nm that shifts bathochromically at low temperature in conjunction with a marked change in the colour of the emission. The emission of MOF I has a maximum at 580 nm and a less pronounced temperature dependence. The peculiar luminescence properties of the two isomers have been interpreted by utilising current knowledge on the excited states properties of Cu^I cubane clusters. The two isomers exhibit a high degree of porosity and can release the disordered solvent molecules trapped in the channels, whilst preserving the crystal structure. Isomer I can be converted into II on exposure to acetonitrile or methanol vapour, whereas II reverts to I when heated in a closed pan at 250 °C.     

Metal complexes of sterically hindered pyrzolylpyridines. The single crystal X-ray structure of [Cu(L)2]BF4 (L = 1-{pyrid-2-yl}-3-{2′,5′-dimethoxyphenyl}pyrazole)

Reaction of potassium 3{5}-(3′,4′-dimethoxyphenyl)pyrazolide with 2-bromopyridine in diglyme at 130°C for 3 days followed by an aqueous quench, affords 1-{pyrid-2-yl}-3-{3′,4′-dimethoxyphenyl}pyrazole (L²) in 69% yield after recrystallization from hot hexanes. Complexation of [Cu(NCMe)₄]BF₄ by 2 molar equivalents of 1-{pyrid-2-yl}-3-{2′,5′-dimethoxyphenyl}pyrazole (L¹) or L² in MeCN at room temperature, followed by concentration and crystallisation with Et₂O, gives [Cu(L)₂]BF₄ L = L¹, L²) in good yields. Treatment of AgBF₄ with L¹ or L² in MeNO₂ similarly gives [Ag(L)₂]BF₄ L = L¹, L²); reaction of AfBF₄ with L² in MeCN gives a product of stoichiometry [Ag(L²)(NCMe)]BF₄. The ¹H NMR spectra of the [M(L)₂]BF₄ complexes show peaks arising from a single coordinated environment. The single crystal X-ray structure of [Cu(L¹)₂]BF₄ shows a tetrahedral complex cation with Cu---N = 2.011(8), 2.036(8), 2.039(8), 2.110(8) Å. The Cu^I centre is close to tetrahedral, the dihedral angle between the least-squares planes formed by the Cu atom and the N donor atoms of the two ligands being 88.3(3)°. Complexation of hydrated Cu(BF₄)₂ by L² in MeCN at room temperature yields [Cu(L₂)₂](BF₄)₂. The cyclic voltammograms of the three Ag^I complexes in MeCN/0.1 M Bu₄ⁿ NPF₆ are suggestive of extensive ligand dissociation in this solvent.