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.     

The nature of the AuI ... AuI Interactions between Cationic [AuL2]+ Complexes in the Solid State

The interaction energy of a [Au{C(NHMe)₂}₂]⁺ ... [Au{C(NHMe)₂}₂]⁺ dimer is investigated using the MP2 method and the LANL2DZ basis set when isolated or embedded in ionic an [Au{C(NHMe)₂}₂]₂anion₂ aggregate, a good model for the environment that these dimers feel in ionic crystals. A repulsive interaction energy is obtained when the dimer is isolated. However, it is possible to find short Au^I ... Au^I separations in [Au{C(NHMe)₂}₂]₂anion₂ aggregates, because in these aggregates the sum of the cation ... anion interactions overweight the sum of the cation ... cation plus anion...anion interactions. This explains why short Au^I ... Au^I separations are found in ionic crystals. The Au^I ... Au^I interaction found in [Au{C(NHMe)₂}₂]₂ anion₂ aggregates shows the same features observed in energetically stable dimers presenting Au^I... Au^I bonds. This makes appropriate to use the name counterion-mediated bonds for the Au^I... Au^I interactions found in [Au{C(NHMe)₂}₂]₂ anion₂ aggregates and ionic crystals.     

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.     

Unraveling the Impact of Gold(I)–Thiolate Motifs on the Aggregation-Induced Emission of Gold Nanoclusters

Aggregation-induced emission (AIE) provides an efficient strategy to synthesize highly luminescent metal nanoclusters (NCs), however, rational control of emission energy and intensity of metal NCs is still challenging. This communication reveals the impact of surface Au^I-thiolate motifs on the AIE properties of Au NCs, by employing a series of water-soluble glutathione (GSH)-coordinated Au complexes and NCs as a model ([Au₁₀SR₁₀], [Au₁₅SR₁₃], [Au₁₈SR₁₄], and [Au₂₅SR₁₈]⁻, SR=thiolate ligand). Spectroscopic investigations show that the emission wavelength of Au NCs is adjustable from visible to the near-infrared II (NIR-II) region by controlling the length of the Au^I-SR motifs on the NC surface. Decreasing the length of Au^I-SR motifs also changes the origin of cluster luminescence from AIE-type phosphorescence to Au⁰-core-dictated fluorescence. This effect becomes more prominent when the degree of aggregation of Au NCs increases in solution.     

Gold(I) and Gold(III) Trifluoromethyl Derivatives

Trifluoromethylation of AuCl₃ by using the Me₃SiCF₃/CsF system in THF and in the presence of [PPh₄]Br proceeds with partial reduction, yielding a mixture of [PPh₄][Au^I(CF₃)₂] ( 1′ ) and [PPh₄][Au^III(CF₃)₄] ( 2′ ) that can be adequately separated. An efficient method for the high‐yield synthesis of 1′ is also described. The molecular geometries of the homoleptic anions [Au^I(CF₃)₂]^? and [Au^III(CF₃)₄]^? in their salts 1′ and [NBu₄][Au^III(CF₃)₄] ( 2 ) have been established by X‐ray diffraction methods. Compound 1′ oxidatively adds halogens, X₂, furnishing [PPh₄][Au^III(CF₃)₂X₂] (X=Cl ( 3 ), Br ( 4 ), I ( 5 )), which are assigned a trans stereochemistry. Attempts to activate C? F bonds in the gold(III) derivative 2′ by reaction with Lewis acids under different conditions either failed or only gave complex mixtures. On the other hand, treatment of the gold(I) derivative 1′ with BF₃?OEt₂ under mild conditions cleanly afforded the carbonyl derivative [Au^I(CF₃)(CO)] ( 6 ), which can be isolated as an extremely moisture‐sensitive light yellow crystalline solid. In the solid state, each linear F₃C‐Au‐CO molecule weakly interacts with three symmetry‐related neighbors yielding an extended 3D network of aurophilic interactions (Au???Au=345.9(1) pm). The high $\tilde \nu $ _CO value (2194 cm^?1 in the solid state and 2180 cm^?1 in CH₂Cl₂ solution) denotes that CO is acting as a mainly σ‐donor ligand and confirms the role of the CF₃ group as an electron‐withdrawing ligand in organometallic chemistry. Compound 6 can be considered as a convenient synthon of the “Au^I(CF₃)” fragment, as it reacts with a number of neutral ligands L, giving rise to the corresponding [Au^I(CF₃)(L)] compounds (L=CNtBu ( 7 ), NCMe ( 8 ), py ( 9 ), tht ( 10 )).     

Unraveling the Impact of Gold(I)–Thiolate Motifs on the Aggregation‐Induced Emission of Gold Nanoclusters

Aggregation‐induced emission (AIE) provides an efficient strategy to synthesize highly luminescent metal nanoclusters (NCs), however, rational control of emission energy and intensity of metal NCs is still challenging. This communication reveals the impact of surface Au^I‐thiolate motifs on the AIE properties of Au NCs, by employing a series of water‐soluble glutathione (GSH)‐coordinated Au complexes and NCs as a model ([Au₁₀SR₁₀], [Au₁₅SR₁₃], [Au₁₈SR₁₄], and [Au₂₅SR₁₈]^?, SR=thiolate ligand). Spectroscopic investigations show that the emission wavelength of Au NCs is adjustable from visible to the near‐infrared II (NIR‐II) region by controlling the length of the Au^I‐SR motifs on the NC surface. Decreasing the length of Au^I‐SR motifs also changes the origin of cluster luminescence from AIE‐type phosphorescence to Au⁰‐core‐dictated fluorescence. This effect becomes more prominent when the degree of aggregation of Au NCs increases in solution.     

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.     

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.     

catena‐Poly­[bromo(ω‐thio­capro­lactam‐κS)­gold(I)](Au—Au)

The title compound, [AuBr(C₆H₁₁NS)]_n, formed through an Au^IIIAu^I reduction process, presents a polymeric structure including Au chains with alternating Au—Au distances of 3.0898 (8) and 3.1181 (8) Å. The coordination geometry is best described on the basis of linear [AuBr(C₆H₁₁NS)] mol­ecules, which are associated into a one‐dimensional polymer via a common aurophilic interaction.     

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.     

[μ‐4,5‐Bis(diphenylphosphino)‐9,9‐dimethylxanthene]bis[(trifluoroacetato)gold(I)] and its dichloromethane 0.58‐solvate

The dinuclear Au^I complex containing the 4,5‐bis(diphenylphosphino)‐9,9‐dimethylxanthene (xantphos) ligand and trifluoroacetate anions exists in a solvent‐free form, [μ‐4,5‐bis(diphenylphosphino)‐9,9‐dimethylxanthene]bis[(trifluoroacetato)gold(I)], [Au₂(C₂F₃O₂)₂(C₃₉H₃₂OP₂)], (I), and as a dichloromethane solvate, [Au₂(C₂F₃O₂)₂(C₃₉H₃₂OP₂)]·0.58CH₂Cl₂, (II). The trifluoroacetate anions are coordinated to the Au^I centres bridged by the xantphos ligand in both compounds. The Au^I atoms are in distorted linear coordination environments in both compounds. The phosphine substituents are in a syn arrangement in the xantphos ligand, which facilitates the formation of short aurophilic Au...Au interactions of 2.8966 (8) Å in (I) and 2.9439 (6) Å in (II).     

Coordination Behavior of a D‐Penicillaminato Aurate(I) Metalloligand Toward Coblat(III) Centers

Treatment of (NH₄)[Au(D‐Hpen‐S)₂](D‐H₂pen = D‐penicillamine) with CoCl₂·6H₂O in an acetate buffer solution, followed by air oxidation, gave neutral Au^ICo^III and anionic Au^I₃Co^III₂ polynuclear complexes, [Au₃Co₃(D‐pen‐N,O,S)₆]([ 1 ]) and [Au₃Co₂(D‐pen‐N,S)₆]^3? ([ 2 ]^3?), which were separated by anion‐exchange column chromatography. Complexes [ 1 ] and [ 2 ]^3? each formed a single isomer, and their structures were determined by single‐crystal X‐ray crystallography. In [ 1 ], each of three [Au(D‐pen‐S)₂]^3?metalloligands coordinates to two Co^III ions in a bis‐tridentate‐N,O,S mode to form a cyclic Au^I₃Co^III₃ hexanuclear structure, in which three [Co(D‐pen‐N,O,S)₂]^? octahedral units and six bridging S atoms adopt trans(O) geometrical and R chiral configurations, respectively. In [ 2 ]^3?, each of three [Au(D‐pen‐S)₂]^3? metalloligands coordinates to two Co^III ions in a bis‐bidentate‐N,S mode to form a Au^I₃Co^III₂ pentanuclear structure, in which two [Co(D‐pen‐N,S)₃]^3? units and six bridging S atoms adopt ∧ and R chiral configurations, respectively.     

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.     

Organic–Inorganic Hybrid Gold Halide Perovskites: Structural Diversity through Cation Size

Crystal structures of a series of organic–inorganic hybrid gold iodide perovskites, formulated as A₂[Au^II₂][Au^IIII₄] [A=methylammonium (MA) ( 1 ) and formamidinium (FA) ( 2 )], A′₂[I₃]_1−x[Au^II₂]_x[Au^IIII₄] [A′=imidazolium (IMD) ( 3 ), guanidinium (GUA) ( 4 ), dimethylammonium (DMA) ( 5 ), pyridinium (PY) ( 6 ), and piperizinium (PIP) ( 7 )], systematically changed depending on the cation size. In addition, triiodide (I₃⁻) ions were partly incorporated into the AuI₂⁻ sites of 3 – 7 , whereas they were not incorporated into those of 1 and 2 . Such a difference comes from the size of the organic cation. Optical absorption spectra showed characteristic intervalence charge-transfer bands from Au^I to Au^III species, and the optical band gap increased as the size of the cation became larger.     

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.     

Front Cover: Safe Entry to Ag(I)/Ag(III) Mixed Valence Salts Containing the Homoleptic Ag(III) Anion [Ag(CF3)4]− (Eur. J. Inorg. Chem. 19/2023)

The synthesis of Naumann's Ag^I/Ag^III mixed valence salt [Ag^I]⁺[Ag^III(CF₃)₄]⁻ ( Ag-1 ) is revisited. Ag-1 is now safely available in half gram scale upon 2e⁻ oxidation of AgF in presence of CF₃SiMe₃ and ambient air. In addition to its unprecedented crystallographic characterization, the use of Ag-1 to build the novel Ag^I/Ag^III salts [ Ag (bpy)₂] -1 , [ Ag (18-crown-6)₂] -1 , [ Ag -crypt-222] -1 and [ Ag (PCy₃)₂] -1 is herein reported, alongside their characterization by NMR, single crystal X-ray diffraction (Sc-XRD) and elemental analysis (EA). The utility of the currently affordable Ag-1 in gold(I) catalysis was demonstrated by the excellent catalytic activity displayed by [{ Au (PPh₃)}₂(μ-Cl)] -1 and [ Au (PPh₃)] -1 in the 5-exo-dig cyclization of N-propargylbenzamide ( 2 ). These cationic Au^I catalysts are accessible from (PPh₃)AuCl and Ag-1 , and outperform the activity of the well-known benchmark catalyst (PPh₃)AuNTf₂.     

Ligand‐Stabilized and Atomically Precise Gold Nanocluster Catalysis: A Case Study for Correlating Fundamental Electronic Properties with Catalysis

We present results from our investigations into correlating the styrene‐oxidation catalysis of atomically precise mixed‐ligand biicosahedral‐structure [Au₂₅(PPh₃)₁₀(SC₁₂H₂₅)₅Cl₂]²⁺ (Au₂₅‐bi) and thiol‐stabilized icosahedral core–shell‐structure [Au₂₅(SCH₂CH₂Ph)₁₈]^? (Au₂₅‐i) clusters with their electronic and atomic structure by using a combination of synchrotron radiation‐based X‐ray absorption fine‐structure spectroscopy (XAFS) and ultraviolet photoemission spectroscopy (UPS). Compared to bulk Au, XAFS revealed low Au–Au coordination, Au? Au bond contraction and higher d‐band vacancies in both the ligand‐stabilized Au clusters. The ligands were found not only to act as colloidal stabilizers, but also as d‐band electron acceptor for Au atoms. Au₂₅‐bi clusters have a higher first‐shell Au coordination number than Au₂₅‐i, whereas Au₂₅‐bi and Au₂₅‐i clusters have the same number of Au atoms. The UPS revealed a trend of narrower d‐band width, with apparent d‐band spin–orbit splitting and higher binding energy of d‐band center position for Au₂₅‐bi and Au₂₅‐i. We propose that the differences in their d‐band unoccupied state population are likely to be responsible for differences in their catalytic activity and selectivity. The findings reported herein help to understand the catalysis of atomically precise ligand‐stabilized metal clusters by correlating their atomic or electronic properties with catalytic activity.     

A charge-separation-type ionic solid composed of hexanuclear complexes with a macrocyclic tetragold(I) metalloligand

The reaction of Na[Co^III(d -ebp)] (d -H₄ebp = N,N′-ethylenebis[d -penicillamine]) with [(Au^ICl)₂(dppe)] (dppe = 1,2-bis[diphenylphosphino]ethane) gave a cationic Au^I₄Co^III₂ hexanuclear complex, [Co^III₂(L^Au4)]²⁺ ([ 1 ]²⁺), where [L^Au4]⁴⁻ is a cyclic tetragold(I) metalloligand with a 32-membered ring, [Au^I₄(dppe)₂(d -ebp)₂]⁴⁻. Complex [ 1 ]²⁺ crystallized with NO₃⁻ to produce a charge-separation (CS)-type ionic solid of [ 1 ](NO₃)₂. In [ 1 ](NO₃)₂, the complex cations are assembled to form cationic supramolecular hexamers of {[ 1 ]²⁺}₆, which are closely packed in a face-centered cubic (fcc) lattice structure. The nitrate anions of [ 1 ](NO₃)₂ were accommodated in hydrophilic and hydrophobic tetrahedral interstices of the fcc structure to form tetrameric and hexameric nitrate clusters of {NO₃⁻}₄ and {NO₃⁻}₆, respectively. An analogous CS-type ionic solid formulated as [Ni^IICo^III(L^Au4)](NO₃) ([ 2 ](NO₃)) was obtained when a 1:1 mixture of Na[Co^III(d -ebp)] and [Ni^II(d -H₂ebp)] was reacted with [(Au^ICl)₂(dppe)], accompanied by the conversion of the diamagnetic, square-planar [Ni^II(d -H₂ebp)] to the paramagnetic, octahedral [Ni^II(d -ebp)]²⁻. While the overall fcc structure in [ 2 ](NO₃) was similar to that of [ 1 ](NO₃)₂, none of the nitrate anions were accommodated in any hydrophobic tetrahedral interstice, reflecting the difference in the complex charges between [ 1 ]²⁺ and [ 2 ]⁺.     

Small Gold(I) and Gold(I)–Silver(I) Clusters by C−Si Auration

Auration of o-trimethylsilyl arylphosphines leads to the formation of gold and gold–silver clusters with ortho-metalated phosphines displaying 3c–2e Au−C−M bonds (M=Au/Ag). Hexagold clusters [Au₆L₄](X)₂ are obtained by reaction of (L−TMS)AuCl with AgX, whereas reaction with AgX and Ag₂O leads to gold–silver clusters [Au₄Ag₂L₄](X)₂. Oxo-trigold(I) species [Au₃O]⁺ were identified as the intermediates in the formation of the silver-doped clusters. Other [Au₅], [Au₄Ag], and [Au₁₂Ag₄] clusters were also obtained. Clusters containing PAu−Au−AuP structural motif display good catalytic activity in the activation of alkynes under homogeneous conditions.