The 3[ndσ*(n+1)pσ] Emissions of Linear Silver(I) and Gold(I) Chains with Bridging Phosphine Ligands

The complexes [Au₃(dcmp)₂][X]₃ {dcmp=bis(dicyclohexylphosphinomethyl)cyclohexylphosphine; X=Cl^? ( 1 ), ClO₄^? ( 2 ), OTf^? ( 3 ), PF₆^? ( 4 ), SCN^?( 5 )}, [Ag₃(dcmp)₂][ClO₄]₃ ( 6 ), and [Ag₃(dcmp)₂Cl₂][ClO₄] ( 7 ) were prepared and their structures were determined by X‐ray crystallography. Complexes 2 – 4 display a high‐energy emission band with λ_max at 442–452 nm, whereas 1 and 5 display a low‐energy emission with λ_max at 558–634 nm in both solid state and in dichloromethane at 298 K. The former is assigned to the ³[5dσ*6pσ] excited state of [Au₃(dcmp)₂]³⁺, whereas the latter is attributed to an exciplex formed between the ³[5dσ*6pσ] excited state of [Au₃(dcmp)₂]³⁺ and the counterions. In solid state, complex [Ag₃(dcmp)₂][ClO₄]₃ ( 6 ) displays an intense emission band at 375 nm with a Stokes shift of ≈7200 cm^?1 from the ¹[4dσ*→5pσ] absorption band at 295 nm. The 375 nm emission band is assigned to the emission directly from the ³[4dσ^*5pσ] excited state of 6 . Density functional theory (DFT) calculations revealed that the absorption and emission energies are inversely proportional to the number of metal ions (n) in polynuclear Au^I and Ag^I linear chain complexes without close metal???anion contacts. The emission energies are extrapolated to be 715 and 446 nm for the infinite linear Au^I and Ag^I chains, respectively, at metal???metal distances of about 2.93–3.02 Å. A QM/MM calculation on the model [Au₃(dcmp)₂Cl₂]⁺ system, with Au???Cl contacts of 2.90–3.10 Å, gave optimized Au???Au distances of 2.99–3.11 Å in its lowest triplet excited state and the emission energies were calculated to be at approximately 600–690 nm, which are assigned to a three‐coordinate Au^I site with its spectroscopic properties affected by Au^I???Au^I interactions.     

Strongly Luminous Tetranuclear Gold(I) Complexes Supported by Tetraphosphine Ligands,meso‐ or rac‐Bis[(diphenylphosphinomethyl)phenylphosphino]methane

A series of tetragold(I) complexes supported by tetraphosphine ligands, meso‐ and rac‐bis[(diphenylphosphinomethyl)phenylphosphino]methane (meso‐ and rac‐dpmppm) were synthesized and characterized to show that the tetranuclear Au^I alignment varies depending on syn‐ and anti‐arrangements of the two dpmppm ligands with respect to the metal chain. The structures of syn‐[Au₄(meso‐dpmppm)₂X]X′₃ (X=Cl; X′=Cl ( 4 a ), PF₆ ( 4 b ), BF₄ ( 4 c )) and syn‐[Au₄(meso‐dpmppm)₂]X₄ (X=PF₆ ( 4 d ), BF₄ ( 4 e ), TfO ( 4 f ); TfO=triflate) involved a bent tetragold(I) core with a counter anion X incorporated into the bent pocket. Complexes anti‐[Au₄(meso‐dpmppm)₂]X₄ (X=PF₆ ( 5 d ), BF₄ ( 5 e ), TfO ( 5 f )) contain a linearly ordered Au₄ string and complexes syn‐[Au₄(rac‐dpmppm)₂X₂]X′₂ (X=Cl, X′=Cl ( 6 a ), PF₆ ( 6 b ), BF₄ ( 6 c )) and syn‐[Au₄(rac‐dpmppm)₂]X₄ (X=PF₆ ( 6 d ), BF₄ ( 6 e ), TfO ( 6 f )) consist of a zigzag tetragold(I) chain supported by the two syn‐arranged rac‐dpmppm ligands. Complexes 4 d–f , 5 d–f , and 6 d–f with non‐coordinative large anions are strongly luminescent in the solid state (λ_max=475–515 nm, Φ=0.67–0.85) and in acetonitrile (λ_max=491–520 nm, Φ=0.33–0.97); the emission was assigned to phosphorescence from ³[d_σ*σ*σ*p_σσσ] excited state of the Au₄ centers on the basis of DFT calculations as well as the long lifetime (a few μs). The emission energy is predominantly determined by the HOMO and LUMO characters of the Au₄ centers, which depend on the bent ( 4 ), linear ( 5 ), and zigzag ( 6 ) alignments. The strong emissions in acetonitrile were quenched by chloride anions through simultaneous dynamic and static quenching processes, in which static binding of chloride ions to the Au₄ excited species should be the most effective. The present study demonstrates that the structures of linear tetranuclear gold(I) chains can be modified by utilizing the stereoisomeric tetraphosphines, meso‐ and rac‐dpmppm, which may lead to fine tuning of the strongly luminescent properties intrinsic to the Au^I₄ cluster centers.     

Pentanuclear Gold(I) Cluster with an Axially Chiral Biaryl Center: Synthesis and Chiral Transformation

We synthesized and structurally characterized a novel pentanuclear gold(I) cluster by a Ag(I)‐mediated organometallic transformation. The racemic mixture of this pentanuclear gold cluster has been successfully transformed into an enantio‐rich hexanuclear cluster compound by adding adscititious chiral species [Au₂(S‐BINAP)₂]²⁺ (S‐BINAP = (S)‐2,2’‐bis(diphenylphosphino)‐1,1’‐binaphthyl). In this process, a [AuPPh₃]⁺ species in the pentanuclear cluster is replaced by [Au₂(S‐BINAP)₂]²⁺. This strategy represents a new method for the designed construction of chiral metal clusters.     

Co‐Adsorption of O2 and CO on Au2−: Infrared Photodissociation Spectroscopy and Theoretical Study of [Au2O2(CO)n]− (n=2–6)

The co‐adsorption of O₂ and CO on anionic sites of gold species is considered as a crucial step in the catalytic CO oxidation on gold catalysts. In this regard, the [Au₂O₂(CO)_n]^? (n=2–6) complexes were prepared by using a laser vaporization supersonic ion source and were studied by using infrared photodissociation spectroscopy in the gas phase. All the [Au₂O₂(CO)_n]^? (n=2–6) complexes were characterized to have a core structure involving one CO and one O₂ molecule co‐adsorbed on Au₂^? with the other CO molecules physically tagged around. The CO stretching frequency of the [Au₂O₂(CO)]^? core ion is observed around =2032–2042 cm^?1, which is about 200 cm^?1 higher than that in [Au₂(CO)₂]^?. This frequency difference and the analyses based on density functional calculations provide direct evidence for the synergy effect of the chemically adsorbed O₂ and CO. The low lying structures with carbonate group were not observed experimentally because of high formation barriers. The structures and the stability (i.e., the inertness in a sense) of the co‐adsorbed O₂ and CO on Au₂^? may have relevance to the elementary reaction steps on real gold catalysts.     

Theoretical study of the electronic spectra of bi‐ and tri‐heteronuclear platinum complexes

The electronic structure and the spectroscopic properties of [Pt(NH₃)₄][Au(CN)₂]₂, [Pt(NH₃)₄][Ag(CN)₂]₂, [Pt(CNCH₃)₄][Pt(CN)₄], and [Pt(CNCH₃)₄][Pd(CN)₄] were studied at the HF, MP2, B3LYP, and PBE levels. In all the complexes, it was found that the nature of the intermetal interactions is consistent with the presence of a high‐ionic contribution (90%) and a dispersion‐type interaction (10%). The absorption spectra of these complexes were calculated by the single‐excitation time‐dependent (TD) method at the HF, B3LYP, and PBE levels. The [Pt(NH₃)₄][M(CN)₂]₂ (M ? Au, Ag) complexes showed a ¹(dσ* → pσ) transition associated with a metal–metal charge transfer. On the other hand, the [Pt(CNCH₃)₄][M(CN)₄] (M ? Pt, Pd) complexes showed a ¹(dσ* → π*) transition associated with a metal‐to‐metal and ligand charge transfer. The values obtained theoretically are in agreement with the experimental range. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Unusual Metal–Metal Bonding in a Dinuclear Pt–Au Complex: Snapshot of a Transmetalation Process

The dinuclear Pt–Au complex [(CNC)(PPh₃)Pt Au(PPh₃)](ClO₄) ( 2 ) (CNC=2,6‐diphenylpyridinate) was prepared. Its crystal structure shows a rare metal–metal bonding situation, with very short Pt–Au and Au–C_ipso(CNC) distances and dissimilar Pt–C_ipso(CNC) bonds. Multinuclear NMR spectra of 2 show the persistence of the Pt–Au bond in solution and the occurrence of unusual fluxional behavior involving the [Pt^II] and [Au^I] metal fragments. The [Pt^II]??? [Au^I] interaction has been thoroughly studied by means of DFT calculations. The observed bonding situation in 2 can be regarded as a model for an intermediate in a transmetalation process.     

Site Preference in Multimetallic Nanoclusters: Incorporation of Alkali Metal Ions or Copper Atoms into the Alkynyl‐Protected Body‐Centered Cubic Cluster [Au7Ag8(C≡CtBu)12]+

The synthesis, structure, substitution chemistry, and optical properties of the gold‐centered cubic monocationic cluster [Au@Ag₈@Au₆(C≡C^tBu)₁₂]⁺ are reported. The metal framework of this cluster can be described as a fragment of a body‐centered cubic (bcc) lattice with the silver and gold atoms occupying the vertices and the body center of the cube, respectively. The incorporation of alkali metal atoms gave rise to [M_nAg_8?nAu₇(C≡C^tBu)₁₂]⁺ clusters (n=1 for M=Na, K, Rb, Cs and n=2 for M=K, Rb), with the alkali metal ion(s) presumably occupying the vertex site(s), whereas the incorporation of copper atoms produced [Cu_nAg₈Au_7?n(C≡C^tBu)₁₂]⁺ clusters (n=1–6), with the Cu atom(s) presumably occupying the capping site(s). The parent cluster exhibited strong emission in the near‐IR region (λ_max=818 nm) with a quantum yield of 2 % upon excitation at λ=482 nm. Its photoluminescence was quenched upon substitution with a Na⁺ ion. DFT calculations confirmed the superatom characteristics of the title compound and the sodium‐substituted derivatives.     

The Structure and Optical Properties of the [Au18(SR)14] Nanocluster

Decreasing the core size is one of the best ways to study the evolution from Au^I complexes into Au nanoclusters. Toward this goal, we successfully synthesized the [Au₁₈(SC₆H₁₁)₁₄] nanocluster using the [Au₁₈(SG)₁₄] (SG=L ‐glutathione) nanocluster as the starting material to react with cyclohexylthiol, and determined the X‐ray structure of the cyclohexylthiol‐protected [Au₁₈(C₆H₁₁S)₁₄] nanocluster. The [Au₁₈(SR)₁₄] cluster has a Au₉ bi‐octahedral kernel (or inner core). This Au₉ inner core is built by two octahedral Au₆ cores sharing one triangular face. One transitional gold atom is found in the Au₉ core, which can also be considered as part of the Au₄(SR)₅ staple motif. These findings offer new insight in terms of understanding the evolution from [Au^I(SR)] complexes into Au nanoclusters.     

Coordination of di- and triimine ligands at ruthenium(II) and ruthenium(III) centers: structural,electrochemical and radical scavenging studies

Herein, we explore the coordination of di- and triimine chelators at ruthenium(II) and ruthenium(III) centers. The reactions of 2,6-bis-((4-tetrahydropyranimino)methyl)pyridine (thppy), N¹,N²-bis((3-chromone)methylene)benzene-1,2-diamine (chb), and tris-((1H-pyrrol-2-ylmethylene)ethane)amine (H₃pym) with trans-[Ru^IICl₂(PPh₃)₃] afforded the diamagnetic ruthenium(II) complex cis-[RuCl₂(thppy)(PPh₃)] (1) and the paramagnetic complexes [mer-Ru₂(μ-chb)Cl₆(PPh₃)₂] (2), and [Ru(pym)] (3), respectively. The complexes were characterized by IR, NMR, and UV–vis spectroscopy and molar conductivity measurements. The structures were confirmed by single crystal X-ray diffraction studies. The redox properties of the metal complexes were probed via cyclic- and squarewave voltammetry. Finally, the radical scavenging capabilities of the metal complexes towards the NO and 2,2-di(4-tert-octylphenyl)-1-picrylhydrazyl (DPPH) radicals were investigated     

A Systematic Investigation of Coinage Metal Carbonyl Complexes Stabilized by Fluorinated Alkoxy Aluminates

The reaction of Cu^I, Ag^I, and Au^I salts with carbon monoxide in the presence of weakly coordinating anions led to known and structurally unknown non‐classical coinage metal carbonyl complexes [M(CO)_n][A] (A=fluorinated alkoxy aluminates). The coinage metal carbonyl complexes [Cu(CO)_n(CH₂Cl₂)_m]⁺[A]^? (n=1, 3; m=4?n), [Au₂(CO)₂Cl]⁺[A]^?, [(OC)_nM(A)] (M=Cu: n=2; Ag: n=1, 2) as well as [(OC)₃Cu???ClAl(OR^F)₃] and [(OC)Au???ClAl(OR^F)₃] were analyzed with X‐ray diffraction and partially IR and Raman spectroscopy. In addition to these structures, crystallographic and spectroscopic evidence for the existence of the tetracarbonyl complex [Cu(CO)₄]⁺[Al(OR^F)₄]^? (R^F=C(CF₃)₃) is presented; its formation was analyzed with the help of theoretical investigations and Born–Fajans–Haber cycles. We discuss the limits of structure determinations by routine X‐ray diffraction methods with respect to the C? O bond lengths and apply the experimental CO stretching frequencies for the prediction of bond lengths within the carbonyl ligand based on a correlation with calculated data. Moreover, we provide a simple explanation for the reported, partly confusing and scattered CO stretching frequencies of [Cu^I(CO)_n] units.     

Gold(I)‐Catalyzed Enantioselective Intermolecular Hydroarylation of Allenes with Indoles and Reaction Mechanism by Density Functional Theory Calculations

Chiral binuclear gold(I) phosphine complexes catalyze enantioselective intermolecular hydroarylation of allenes with indoles in high product yields (up to 90 %) and with moderate enantioselectivities (up to 63 % ee). Among the gold(I) complexes examined, better ee values were obtained with binuclear gold(I) complexes, which displayed intramolecular Au^I Au^I interactions. The binuclear gold(I) complex 4c [(AuCl)₂( L3 )] with chiral biaryl phosphine ligand (S)‐(−)‐MeO‐biphep ( L3 ) is the most efficient catalyst and gives the best ee value of up to 63 %. Substituents on the allene reactants have a slight effect on the enantioselectivity of the reaction. Electron‐withdrawing groups on the indole substrates decrease the enantioselectivity of the reaction. The relative reaction rates of the hydroarylation of 4‐X‐substituted 1,3‐diarylallenes with N‐methylindole in the presence of catalyst 4c [(AuCl)₂( L3 )] / AgOTf [ L3 =(S)‐(−)‐MeO‐biphep], determined through competition experiments, correlate (r²=0.996) with the substituent constants σ. The slope value is −2.30, revealing both the build‐up of positive charge at the allene and electrophilic nature of the reactive Au^I species. Two plausible reaction pathways were investigated by density functional theory calculations, one pathway involving intermolecular nucleophilic addition of free indole to aurated allene intermediate and another pathway involving intramolecular nucleophilic addition of aurated indole to allene via diaurated intermediate E2 . Calculated results revealed that the reaction likely proceeds via the first pathway with a lower activation energy. The role of Au^I Au^I interactions in affecting the enantioselectivity is discussed.     

Copper(II)‐ and gold(III)‐mediated cyclization of a thiourea to a substituted 2‐aminobenzothiazole

Benzothiazole derivatives are a class of privileged molecules due to their biological activity and pharmaceutical applications. One route to these molecules is via intramolecular cyclization of thioureas to form substituted 2‐aminobenzothiazoles, but this often requires harsh conditions or employs expensive metal catalysts. Herein, the copper(II)‐ and gold(III)‐mediated cyclizations of thioureas to substituted 2‐aminobenzothiazoles are reported. The single‐crystal X‐ray structures of the thiourea N‐(3‐methoxyphenyl)‐N ′‐(pyridin‐2‐yl)thiourea, C₁₃H₁₃N₃OS, and the intermediate metal complexes aquabis[5‐methoxy‐N‐(pyridin‐2‐yl‐κN )‐1,3‐benzothiazol‐2‐amine‐κN ³]copper(II) dinitrate, [Cu(C₁₃H₁₁N₃OS)₂(H₂O)](NO₃)₂, and bis{2‐[(5‐methoxy‐1,3‐benzothiazol‐2‐yl)amino]pyridin‐1‐ium} dichloridogold(I) chloride monohydrate, (C₁₃H₁₂N₃OS)₂[AuCl₂]Cl·H₂O, are reported. The copper complex exhibits a distorted trigonal–bipyramidal geometry, with direct metal‐to‐benzothiazole‐ligand coordination, while the gold complex is a salt containing the protonated uncoordinated benzothiazole, and offers evidence that metal reduction (in this case, Au^III to Au^I) is required for the cyclization to proceed. As such, this study provides further mechanistic insight into the role of the metal cations in these transformations.     

The first example of a two‐coordinated AuI atom bonded to an FeII atom and an N‐heterocyclic carbene (NHC) ligand

The aurophilicity exhibited by Au^I complexes depends strongly on the nature of the supporting ligands present and the length of the Au–element (Au—E) bond may be used as a measure of the donor–acceptor properties of the coordinated ligands. A binuclear iron–gold complex, [1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene‐2κC²]dicarbonyl‐1κ²C‐(1η⁵‐cyclopentadienyl)gold(I)iron(II)(Au—Fe) benzene trisolvate, [AuFe(C₅H₅)(C₂₇H₃₆N₂)(CO)₂]·3C₆H₆, was prepared by reaction of K[CpFe(CO)₂] (Cp is cyclopentadienyl) with (NHC)AuCl [NHC = 1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene]. In addition to the binuclear complex, the asymmetric unit contains three benzene solvent molecules. This is the first example of a two‐coordinated Au atom bonded to an Fe and a C atom of an N‐heterocyclic carbene.     

Neue Gold‐Selen‐Komplexverbindungen: Synthesen und Strukturen von [Au10Se4(dpppe)4]Br2, [Au2Se(dppbe)]∞, [(Au3Se)2(dppbp)3]Cl2 und [Au34Se14(tpep)6(tpepSe)2]Cl6

Novel Gold Selenium Complexes: Syntheses and Structures of [Au₁₀Se₄(dpppe)₄]Br₂, [Au₂Se(dppbe)]_∞, [(Au₃Se)₂(dppbp)₃]Cl₂, and [Au₃₄Se₁₄(tpep)₆(tpep^Se)₂]Cl₆ The reaction of gold phosphine complexes [(AuX)(PR₃)] (X= halogen; R = org. group) with Se(SiMe₃)₂ yield to new chalcogeno bridged gold complexes. Especially within the use of polydentate phosphine ligands cluster complexes like [Au₁₀Se₄(dpppe)₄]Br₂ ( 1 ) (dpppe = 1, 5‐Bis(diphenylphosphino)pentane), [Au₂Se(dppbe)]_∞ ( 2 ) (1, 4‐Bis(diphenylphosphino)benzene), [(Au₃Se)₂(dppbp)₃]Cl₂ ( 3 ) (dppbp = 4, 4′‐Bis‐diphenylphosphino)biphenyl) und [Au₃₄Se₁₄(tpep)₆(tpep^Se)₂]Cl₆ ( 4 ) (tpep = 1, 1, 1‐Tris(diphenylphosphinoethyl)phosphine, tpep^Se = 1, 1‐Bis(diphenylphosphinoethyl)‐1‐(diphenylselenophosphinoethylphosphine) could be isolated and their structures could be determined by X‐ray diffraction. ( 1: Space group P1 (No. 2), Z = 2, a = 1642.1(11), b = 1713.0(9), c = 2554.0(16) pm, α = 80.41(3)°, β = 76.80(4)°, γ = 80.92(4)°; 2: Space group P2₁/n (No. 14), Z = 4, a = 947.3(2), b = 1494.9(3), c = 2179.6(7) pm, β = 99.99(3)°; 3: Space group P2₁/c (No. 14), Z = 8, a = 2939.9(6), b = 3068.4(6), c = 3114.5(6) pm, β = 109.64(3)°; 4: Space group P1 (No. 2), Z = 1, a = 2013.7(4), b = 2420.6(5), c = 2462.5(5) pm, α = 77.20(3), β = 74.92(3), γ = 87.80(3)°).     

Same Magic Number but Different Arrangement: Alkynyl‐Protected Au25 with D3 Symmetry

Two homoleptic alkynyl‐protected gold clusters with compositions of Na[Au₂₅(C≡CAr)₁₈] and (Ph₄P)[Au₂₅(C≡CAr)₁₈] (Na? 1 and Ph₄P? 1 , Ar=3,5‐bis(trifluoromethyl)phenyl) were synthesized via a direct reduction method. 1 is a magic cluster analogous to [Au₂₅(SR)₁₈]^? in terms of electron counts and metal‐to‐ligand ratio. Single‐crystal structure analysis reveals that 1 has an identical Au₁₃ kernel to [Au₂₅(SR)₁₈]^?, but adopts a distinctly different arrangement of the six peripheral dimer staple motifs. The steric hindrance of alkynyl ligands is responsible for the D₃ arrangement of Au₂₅. The introduction of alkynyl also significantly changes the optical absorption features of the nanocluster as supported by DFT calculations. This magic cluster confirms that there is a similar but quite different parallel alkynyl‐protected metal cluster universe in comparison to the thiolated one.     

Aurophilic Interactions in the Self‐Assembly of Gold Nanoclusters into Nanoribbons with Enhanced Luminescence

Aurophilic interactions (Au^I???Au^I) are crucial in directing the supramolecular self‐assembly of many gold(I) compounds; however, this intriguing chemistry has been rarely explored for the self‐assembly of nanoscale building blocks. Herein, we report on studies on aurophilic interactions in the structure‐directed self‐assembly of ultrasmall gold nanoparticles or nanoclusters (NCs, <2 nm) using [Au₂₅(SR)₁₈]^? (SR=thiolate ligand) as a model cluster. The self‐assembly of NCs is initiated by surface‐motif reconstruction of [Au₂₅(SR)₁₈]^? from short SR‐[Au^I‐SR]₂ units to long SR‐[Au^I‐SR]_x (x>2) staples accompanied by structure modification of the intrinsic Au₁₃ kernel. Such motif reconstruction increases the content of Au^I species in the protecting shell of Au NCs, providing the structural basis for directed aurophilic interactions, which promote the self‐assembly of Au NCs into well‐defined nanoribbons in solution. More interestingly, the compact structure and effective aurophilic interactions in the nanoribbons significantly enhance the luminescence intensity of Au NCs with an absolute quantum yield of 6.2 % at room temperature.     

A Ligand‐Protected Golden Fullerene: The Dipyridylamido Au328+ Nanocluster

A golden fullerene Au₃₂ cluster has been synthesized with amido and phosphine ligands as the protecting agents. Single‐crystal X‐ray structural analysis revealed that this gold nanocluster, [Au₃₂(Ph₃P)₈(dpa)₆] (SbF₆)₂ (Hdpa=2,2′‐dipyridylamine), has a stable pseudo‐I_h Au₃₂⁸⁺ core with S₆ symmetry, which features an Au₁₂@Au₂₀ Keplerate cage co‐protected by Ph₃P and dpa ligands. Quantum‐chemical studies were conducted to elucidate the origin of the special stability of this cluster, and suggest that it is electronically stabilized through metal–ligand interactions.     

Luminescence properties and optimized structural conformations of the S0, S1 and T1 states of a tetranuclear formamidinate complex based on AuI and AgI metal ions

N,N′‐Bis(pyridin‐4‐yl)formamidine (4‐pyfH) was reacted with Au^I and Ag^I metal salts to form a novel tetranuclear complex, tetrakis[μ‐N,N′‐bis(pyridin‐4‐yl)formamidinato]digold(I)disilver(I), [Ag₂Au₂(C₁₁H₉N₄)₂] or [Au_xAg_4–x(4‐pyf)₄] (x = 0–4), 1 , which is supported by its metallophilicity. Due to the potential permutation of the coordinated metal ions, six different canonical structures of 1 can be obtained. Complex 1 shows an emission at 501 nm upon excitation at 375 nm in the solid state and an emission at 438 nm upon excitation at 304 nm when dispersed in methanol. Time‐dependent density functional theory (TD‐DFT) calculations confirmed that these emissions can be ascribed to metal‐to‐ligand charge transfer (MLCT) processes. Moreover, the calculations of the optimized structural conformations of the S₀ ground state, and the S₁ and T₁ excited states are discussed and suggest a distorted planar conformation for the tetranuclear Au₂Ag₂ complex.     

Formation,Expansion, and Interconversion of Metallarings in a Sulfur‐Bridged AuICoIII Coordination System

A novel Au^ICo^III coordination system that is derived from the newly prepared [Co(D ‐nmp)₂]^? ( 1 ^?; D ‐nmp=N‐methyl‐D ‐penicillaminate) and a gold(I) precursor Au^I is reported. Complex 1 ^? acts as a sulfur‐donating metallaligand and reacts with the gold(I) precursor to give [Au₂Co₂(D ‐nmp)₄] ( 2 ), which has an eight‐membered Au^I₂Co^III₂ metallaring. Treatment of 2 with [Au₂(dppe)₂]²⁺ (dppe=1,2‐bis(diphenylphosphino)ethane) leads to the formation of [Au₄Co₂(dppe)₂(D ‐nmp)₄]²⁺ ( 3 ²⁺), which consists of an 18‐membered Au^I₄Co^III₂ metallaring that accommodates a tetrahedral anion (BF₄^?, ClO₄^?, ReO₄^?). In solution, the metallaring structure of 3 ²⁺ is readily interconvertible with the nine‐membered Au^I₂Co^III metallaring structure of [Au₂Co(dppe)(D ‐nmp)₂]⁺ ( 4 ⁺); this process depends on external factors, such as solvent, concentration, and nature of the counteranion. These results reveal the lability of the Au? S and Au? P bonds, which is essential for metallaring expansion and contraction.     

Formation,Expansion, and Interconversion of Metallarings in a Sulfur‐Bridged AuICoIII Coordination System

A novel Au^ICo^III coordination system that is derived from the newly prepared [Co(D ‐nmp)₂]⁻ ( 1 ⁻; D ‐nmp=N‐methyl‐D ‐penicillaminate) and a gold(I) precursor Au^I is reported. Complex 1 ⁻ acts as a sulfur‐donating metallaligand and reacts with the gold(I) precursor to give [Au₂Co₂(D ‐nmp)₄] ( 2 ), which has an eight‐membered Au^I₂Co^III₂ metallaring. Treatment of 2 with [Au₂(dppe)₂]²⁺ (dppe=1,2‐bis(diphenylphosphino)ethane) leads to the formation of [Au₄Co₂(dppe)₂(D ‐nmp)₄]²⁺ ( 3 ²⁺), which consists of an 18‐membered Au^I₄Co^III₂ metallaring that accommodates a tetrahedral anion (BF₄⁻, ClO₄⁻, ReO₄⁻). In solution, the metallaring structure of 3 ²⁺ is readily interconvertible with the nine‐membered Au^I₂Co^III metallaring structure of [Au₂Co(dppe)(D ‐nmp)₂]⁺ ( 4 ⁺); this process depends on external factors, such as solvent, concentration, and nature of the counteranion. These results reveal the lability of the Au S and Au P bonds, which is essential for metallaring expansion and contraction.