Single‐Crystal‐to‐Single‐Crystal Transformation and Solvochromic Luminescence of a Dinuclear Gold(I)–(Aza‐[18]crown‐6)dithiocarbamate Compound

The treatment of [AuCl(SMe₂)] with an equimolar amount of NaO₅NCS₂ (O₅NCS₂=(aza‐[18]crown‐6)dithiocarbamate) in CH₃CN gave [Au₂(O₅NCS₂)₂] ? 2 CH₃CN ( 2? 2 CH₃CN), and its crystal structure displays a dinuclear gold(I)‐azacrown ether ring and an intermolecular gold(I) ??? gold(I) contact of 2.8355(3) Å in crystal lattices. It is noted that two other single crystals of 2 ?tert‐butylbenzene?H₂O and 2? 0.5 m‐xylene can be successfully obtained from a single‐crystal‐to‐single‐crystal (SCSC) transformation process by immersing single crystals of 2? 2 CH₃CN in the respective solvents, and both also show intermolecular gold(I) ??? gold(I) contacts of 2.9420(5) and 2.890(2)–2.902(2) Å, respectively. Significantly, the emissions of all three 2 ?solvates are well correlated with their respective intermolecular gold(I) ??? gold(I) contacts, where such contacts increase with 2? 2 CH₃CN (2.8355(3) Å)< 2? 0.5 m‐xylene (2.890(2)–2.902(2) Å)< 2? tert‐butylbenzene?H₂O (2.9420(5) Å), and their emission energies increase with 2? 2 CH₃CN (602 nm)< 2? 0.5 m‐xylene (583 nm)< 2? tert‐butylbenzene?H₂O (546 nm) as well. In this regard, we further examine the solvochromic luminescence for some other aromatics, and finally their emissions are within 546–602 nm. Obviously, the above results are mostly ascribed to the occurrence of intermolecular gold(I) ??? gold(I) contacts in 2 ?solvates, which are induced by the presence of various solvates in the solid state, as a key role to be responsible for their solvochromic luminescence.     

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 [Au₂(mes)₂(μ‐LL)] (LL=dppe: 1,2‐bis(diphenylphosphano)ethane 1 a , and water‐soluble dppy: 1,2‐bis(di‐3‐pyridylphosphano)ethane 1 b ) with Ag⁺ and Cu⁺ lead to the formation of a family of heterometallic clusters with mesityl bridging ligands of the general formula [Au₂M(μ‐mes)₂(μ‐LL)][A] (M=Ag, A=ClO₄^?, LL=dppe 2 a , dppy 2 b ; M=Ag, A=SO₃CF₃^?, LL=dppe 3 a , dppy 3 b ; M=Cu, A=PF₆^?, LL=dppe 4 a , dppy 4 b ). The new compounds were characterized by different spectroscopic techniques and mass spectrometry The crystal structures of [Au₂(mes)₂(μ‐dppy)] ( 1 b ) and [Au₂Ag(μ‐mes)₂(μ‐dppe)][SO₃CF₃] ( 3 a ) were determined by a single‐crystal X‐ray diffraction study. 3 a in solid state is not a cyclic trinuclear Au₂Ag derivative but it gives an open polymeric structure instead, with the {Au₂(μ‐dppe)} fragments “linked” by {Ag(μ‐mes)₂} units. The very short distances of 2.7559(6) Å (Au? Ag) and 2.9229(8) Å (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 [Au₂M(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 3 a . In solid state the heterometallic Au₂M complexes with dppe ( 2 a – 4 a ) show a shift of emission maxima (from ca. 430 to the range of 520‐540 nm) as compared to the parent dinuclear organometallic product 1 a while the complexes with dppy ( 2 b–4 b ) display a more moderate shift (505 for 1 b to a max of 563 nm for 4 b ). More importantly, compound [Au₂Ag(μ‐mes)₂(μ‐dppy)]ClO₄ ( 2 b ) resulted luminescent in diluted DMSO solution at room temperature. Previously reported compound [Au₂Cl₂(μ‐LL)] (LL dppy 5 b ) was also studied for comparative purposes. The antimicrobial activity of 1–5 and Ag[A] (A=ClO₄^?, SO₃CF₃^?) against Gram‐positive and Gram‐negative bacteria and yeast was evaluated. Most tested compounds displayed moderate to high antibacterial activity while heteronuclear Au₂M derivatives with dppe ( 2 a – 4 a ) 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 1 a or silver salts. Au₂Ag compounds with dppy ( 2 b , 3 b ) were also potent against fungi.     

Polysiloxane‐Based Luminescent Elastomers Prepared by Thiol–ene “Click” Chemistry

Side‐chain vinyl poly(dimethylsiloxane) has been modified with mercaptopropionic acid, methyl 3‐mercaptopropionate, and mercaptosuccinic acid. Coordinative bonding of Eu^III to the functionalized polysiloxanes was then carried out and crosslinked silicone elastomers were prepared by thiol–ene curing reactions of these composites. All these europium complexes could be cast to form transparent, uniform, thin elastomers with good flexibility and thermal stability. The networks were characterized by FTIR, NMR, UV/Vis, and luminescence spectroscopy as well as by scanning electron microscopy, thermogravimetric analysis, and X‐ray photoelectron spectroscopy. The europium elastomer luminophores exhibited intense red light at 617 nm under UV excitation at room temperature due to the ⁵D₀→⁷F₂ transition in Eu^III ions. The newly synthesized luminescent materials offer many advantages, including the desired mechanical flexibility. They cannot be dissolved or fused, and so they have potential for use in optical and electronic applications.     

”The criterion was excellence“

The 3rd Euchems Conference is an ideal platform for spotlighting chemistry as the key source of sustainable solutions to the mega‐topics and challenges facing all of us today: energy, food supplies, and resources in a healthy environment. Nachrichten aus der Chemie talked with Francois Diederich and Andreas Hirsch, chairs of the Scientific Committee.     

Experimental and Theoretical Evidence of the Existence of Gold(I)⋅⋅⋅Mercury(II) Interactions in Solution through Fluorescence‐Quenching Measurements

Heteronuclear complexes {[Hg(R)₂][Au(R′)(PMe₃)]₂}_n (R=R′=C₆Cl₂F₃ ( 3 ); R=R′=C₆F₅ ( 4 ); R=C₆Cl₂F₃, R′=C₆F₅ ( 5 ); R=C₆F₅, R′=C₆Cl₂F₃ ( 6 )) were prepared by the treatment of the corresponding organomercury compounds, [Hg(C₆X₅)₂], with two equivalents of [Au(C₆X₅)(PMe₃)]. Their crystal structures, as determined by using X‐ray diffraction methods, display Au???Hg interactions. Although only compound 4 and 5 show luminescence in the solid state, all of these compounds quench the fluorescence of naphthalene in solution. Solution studies of these derivatives suggest a cooperative effect of the gold(I) center in switching on the quenching capabilities of the [Hg(C₆X₅)₂] synthon with naphthalene. Theoretical studies confirmed the quenching ability of the organomercury species in the presence of gold.     

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.     

Elementary Steps of Gold Catalysis: NMR Spectroscopy Reveals the Highly Cationic Character of a “Gold Carbenoid”

What are you? Even though the metal‐induced ring opening of 3,3‐disubstituted cyclopropenes is known to serve as a genuine carbene generator, the use of Au^I in this reaction leads to a reactive intermediate with highly cationic character. This result has important implications for gold catalysis in general, which in the past has been commonly attributed to the intervention of gold carbenes.

     

“Click” Chemistry Mildly Stabilizes Bifunctional Gold Nanoparticles for Sensing and Catalysis

A large family of bifunctional 1,2,3‐triazole derivatives that contain both a polyethylene glycol (PEG) chain and another functional fragment (e.g., a polymer, dendron, alcohol, carboxylic acid, allyl, fluorescence dye, redox‐robust metal complex, or a β‐cyclodextrin unit) has been synthesized by facile “click” chemistry and mildly coordinated to nanogold particles, thus providing stable water‐soluble gold nanoparticles (AuNPs) in the size range 3.0–11.2 nm with various properties and applications. In particular, the sensing properties of these AuNPs are illustrated through the detection of an analogue of a warfare agent (i.e., sulfur mustard) by means of a fluorescence “turn‐on” assay, and the catalytic activity of the smallest triazole–AuNPs (core of 3.0 nm) is excellent for the reduction of 4‐nitrophenol in water.     

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.     

Enhanced Luminescent Properties of an Open‐Shell (3,5‐Dichloro‐4‐pyridyl)bis(2,4,6‐trichlorophenyl)methyl Radical by Coordination to Gold

A gold(I) complex containing an open‐shell luminescent (3,5‐dichloro‐4‐pyridyl)bis(2,4,6‐trichlorophenyl)methyl (PyBTM) radical was prepared. The complex showed fluorescence centered mainly on the coordinated PyBTM ligand. The photophysical and photochemical properties were positively modulated upon coordination to Au^I; the photoluminescence quantum yield, fluorescence wavelength, and the stability in the photoexcited state all increased.