Cuprophilic Interactions in and between Molecular Entities

Synthesis and Characterization of Bimetallic Copper(I) Complexes Supported by a Hexadentate Naphthyridine-Based Macrocycle Ligand

Herein, we report the synthesis, characterization, and binding properties of a new ligand, N,N'-di-tert-butyl-3,7-diaza-1,5(2,7)-1,8-naphthyridinacyclooctaphane (tBuN6), with copper (I), CuI, centers. We demonstrate the flexibility and the ability of tBuN6 to adopt various conformations in solution and when coordinated to CuIcenters. NMR studies exhibit the labile coordination nature of CuI. However, the lability of the complexes is blocked by counterion exchange, which enables the use of less coordinating solvents such as tetrahydrofuran (THF) and avoids using acetonitrile. Thus, the exchange of [BF4]- with tetrakis 3,5-bis(trifluoromethyl)phenyl borate, [B(ArF)4]-, in 1·BF4, [Cu2(MeCN)2(tBuN6)][BF4], generates 1·B(ArF)4, which is stable in THF and reacts under a CO atmosphere to generate a syn,syn bis(carbonyl) complex. This complex is sufficiently stable in solution under CO and Ar atmosphere to be characterized by NMR and IR spectroscopy, the latter revealing two stretching bands for the CO bound to the CuI-centers at 2102 and 2088 cm-1.

Enhanced blue phosphorescence in platinum acetylide complexes via a secondary heavy metal and anion-controlled aggregation

Organoplatinum compounds represent a promising class of blue-phosphorescent molecules for electroluminescent color displays. Much recent work has focused on decreasing the nonradiative rate constant (k nr) to improve the photoluminescence quantum yield (Φ PL) of these compounds, but in most cases small radiative rate constants (k r) lead to long excited-state lifetimes (τ) poorly suited for electroluminescence applications. In this work, we present an approach to increase k r and Φ PL in blue-phosphorescent platinum acetylide complexes with the general formula cis-[Pt(CN-R)2(C[triple bond, length as m-dash]C-2-py)2] (CN-R is an alkyl isocyanide and C[triple bond, length as m-dash]C-2-py is 2-pyridylacetylide). This method incorporates secondary heavy metals, Cu(i) or Ag(i), bound by the pyridyl moieties. We observe the formation of dimer complexes in the solid state due to noncovalent interactions between the secondary metal and the acetylide ligands, especially strong in the case of Cu(i). Incorporation of Cu(i) also erodes the desired blue-phosphorescence by introducing a low-lying metal-to-ligand charge transfer (3MLCT) state that dominates the observed phosphorescence. In the complexes bound to Ag(i), we find that phosphorescence profile is strongly dependent on the counteranion, which we propose is caused by different degrees of aggregation. With this insight, we show that coordination of AgBArF 4 (BArF 4 - = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate), with a large noncoordinating counteranion, inhibits aggregation and results in a 4-8× increase in k r and a 5-10× increase in Φ PL while preserving a pure blue phosphorescence profile.

Mechanistic Insights into Molecular Copper Hydride Catalysis: the Kinetic Stability of CuH Monomers toward Aggregation is a Critical Parameter for Catalyst Performance

The activity of molecular copper hydride (CuH) complexes toward the selective insertion of unsaturated hydrocarbons under mild conditions has contributed significantly to versatile methodologies for upgrading these feedstocks. However, these catalysts are particularly susceptible to deleterious aggregation, leading to the depletion of active CuH species. Little is known about the mechanisms of CuH aggregation, how it influences overall catalyst performance, and how it can be controlled. We address these challenges with mechanistic studies on a model reaction of unactivated alkene hydroboration catalyzed by (IPr*CPh3)CuH (LCuH). We report a comprehensive mechanistic investigation of this system, identifying an aggregation pathway that continuously depletes catalytically active LCuH to form inactive CuH clusters during turnover. Deactivation of LCuH is controlled primarily by the competition between the kinetics of the initial LCuH dimerization step and that of alkene insertion into LCuH. We therefore propose that a comprehensive understanding of CuH catalyst performance must account for the kinetics of the initial LCuH dimerization step, revising a previously explored thermodynamic understanding of CuH aggregation, where the concentration of active species is controlled by equilibria established between CuH clusters and monomers. With a series of (NHC)CuH congeners (NHC = N-heterocyclic carbene), we demonstrate that ostensibly minor structural modifications to the ligand peripheries can drastically affect the LCuH dimerization kinetics, while maintaining reactivity toward on-cycle alkene insertion. We employed a computational approach based on molecular dynamics simulations to provide an in-depth understanding of how specific structural ligand modifications can substantially increase the kinetic stability of monomeric CuH catalysts. Our combined experimental and computational studies suggest strategies for rational ligand design that can be broadly applied to molecular catalyst systems that are susceptible to deactivation via aggregation pathways.

Endohedral Coordination of Bulky Substrates in Metalloenzyme-Like Organometallic Nanotubes

Artificial receptors inspired by metalloenzymes share three key properties: a structurally flexible cavity, substrate binding via metal-ligand coordination, and metal-based redox activity. Herein, we report an organometallic nanotube with such features based on our supramolecular pillarplex platform, incorporating eight CuI centers in its cavitand walls. The structurally adaptable cavity of this receptor enables the endohedral coordination of tetrahydrofuran (THF) as a hydrophilic model substrate with remarkable binding affinity despite a steric mismatch between the host and guest. Evidence from SC-XRD, 1H NMR titration in aqueous solution, and DFT modelling confirms that metal-ligand coordination governs substrate binding. Electrochemical analysis of a derived rotaxane reveals metal-centered redox activity.

Adaptive Coordination Behavior of Bisphosphanylphosphanido-Ligands Toward Group 2, 11 and 12 Metal Ions

A series of alkaline earth metal complexes (Mg-Ba) with the anionic ferrocenylene-bridged bisphosphanylphosphanide ligand [Fe(C5H4PC4H9)2P]- has been prepared by metalation of the corresponding bisphosphanylhydrophosphane (Fe(C5H4PC4H9)2PH). The resulting complexes have been characterized by multinuclear NMR spectroscopy and SC-XRD. Furthermore, the closely related zinc phosphanide, and rare, mononuclear coinage metal phosphanides were synthesized and investigated for comparison. The range of coordination modes observed for the phosphanide ligand included mono-, bi-, and tridentate modi and their respective combinations, whereas no μ2-bridging of the phosphanide center has been observed. The value of the 1JPP coupling constant was found to be a good probe to track the coordination motif consistent with the situation in solid state.

Red Emissive 1D Copper(I) Thiolates and Green Emissive 2D Copper(I) Halide Thiolates Displaying Second Harmonic Generation and Two-Photon Absorption Processes

Copper(I), as a d10 metal, is a promising affordable noncritical raw material finding great interest for the development of photoluminescent materials. Halide and thiolate-based copper(I) compounds are known for their efficient emission and good stability. In order to rationalize the effect of these two anions in the structure and photoemission of Cu(I) compounds, two new families of coordination polymers have been synthesized: the copper(I)-thiolates: [Cu(p-SPhX)]n (X = F, Cl, Br), and the copper halide thiolates: [Cu3Cl(p-SPhX)2]n (X = F, Cl, Br). The two families display different structural dimensionalities: 1D [Cu(p-SPhX)]n versus 2D [Cu3Cl(p-SPhX)2]n and they exhibit distinct photophysical properties: [Cu(p-SPhX)]n shows usual solid-state red emission, while [Cu3Cl(p-SPhX)2]n hasintense solid-state green anti-Stokes emission, associated, for the noncentrosymmetric compounds, X = F and Br, to non-linear optical (NLO) response, pointing out the effect of the weak halogen interactions of the thiolate ligands on the symmetry and the properties.

Dynamic Copper(I) and Silver(I) Complexes of Tri-tert-butyl-cyclotriphosphane

The reaction of cyclo-(P3tBu3) with CuI and AgI salts led to the di- and tetranuclear complexes [Cun(μ-Br)n{μ-cyclo-(P3tBu3)-κP1,κP2}2] with n = 2 (1) and n = 4 (2) and [Agn(OTf)n(CH3CN)2 n -2{μ-cyclo-(P3tBu3)-κP1,κP2}2] with n = 2 (4) and n = 4 (5). Complexes 1, 2, 4 and 5 were isolated as crystalline powders or single crystals and characterized by X-ray diffraction. In solution, these complexes exhibit a dynamic equilibrium which involves continuous dissociation and reforming of phosphorus-metal bonds leading to isomeric intermediates. This behavior was demonstrated by low-temperature 31P{1H} NMR spectroscopy and the conclusions were corroborated by DFT calculations.

Unraveling cation-cation "attraction" in argentophilic interaction in 2,2'-bipydine coordinated silver complex

The nature of argentophilic interaction in the 2,2'-bipyridine-coordinated silver complex, which manifests counterintuitive cation-cation "attraction," is attributed to ligand stacking and solvation effects in the present article. While charged closed-shell transition metal complexes aggregating spontaneously to form oligomers has long been observed experimentally, the interpretation of the nature of so-called metallophilicity is still ongoing. For the dimer [(2,2'-bpy)2Ag]22+, qualitative electrostatic potential, non-covalent interaction, atoms-in-molecules analyses, and quantitative energy decomposition analysis calculations indicate that the electrostatic repulsion between two like formal charges at silver centers can be overcome by long-range dispersion attraction and short-range electronic correlation from ligands. In addition, delocalizing the net charges on silvers over the whole ligands can decrease electrostatic repulsion of metal centers to stabilize oligomers. The vital role of the screening effect of solvent has also been realized in the bound binding of the title system. Overall, this research highlights the importance of ligand stacking to argentophilicity, while d10-d10 attraction of silver centers presents quite little contribution.

Silyl- and germyl-bridged neutral square-planar Ag4 clusters with short Ag-Ag distances exhibiting red emission

We report silyl- and germyl-bridged neutral square-planar Ag4 clusters with very short Ag-Ag distances (2.695 and 2.704 Å), as revealed by single-crystal X-ray diffraction analysis. On the basis of the results of theoretical calculations, we attribute these short distances to attractive Ag-Ag interactions that reduce the optical energy gap, resulting in a red emission reaching wavelengths of up to 700 nm. These wavelengths are among the longest observed for emissions from Ag4 clusters.

Cu(I)-Induced G-Quartets: Robust Supramolecular Polymers Exhibiting Heating-Induced Aqueous Phase Transitions Into Gel or Precipitate

Certain proteins and synthetic covalent polymers experience aqueous phase transitions, driving functional self-assembly. Herein, we unveil the ability of supramolecular polymers (SPs) formed by G4.Cu+ to undergo heating-induced unexpected aqueous phase transitions. For the first time, guided by Cu+, guanosine (G) formed a highly stable G-quartet (G4.Cu+)/G-quadruplex as a non-canonical DNA secondary structure with temperature tolerance, distinct from the well-known G4.K+. The G4.Cu+ self-assembled in water through π-π stacking, metallophilic and hydrophobic interactions, forming thermally robust SPs. This enhanced stability is attributed to the stronger coordination of Cu+ to four carbonyl oxygens of G-quartet and the presence of Cu+- - -Cu+ attractive metallophilic interactions in Cu+-induced G-quadruplex, exhibiting a significantly higher interaction energy than K+ as determined computationally. Remarkably, the aqueous SP solution exhibited heating-induced phase transitions-forming a hydrogel through dehydration-driven crosslinking of SPs below cloud temperature (Tcp) and a hydrophobic collapse-induced solid precipitate above Tcp, showcasing a lower critical solution temperature (LCST) behavior. Notably, this LCST behavior of G4.Cu+ SP originates from biomolecular functionality rather than commonly exploited thermo-responsive oligoethylene glycols with supramolecular assemblies. Furthermore, exploiting the redox reversibility of Cu+/Cu2+, we demonstrated control over the assembly and disassembly of G-quartets/G-quadruplex and gelation reversibly.

Ligand-Induced Intramolecular Cuprophilic and Argentophilic Interactions in Bimetallic Cu(I) and Ag(I) Phosphine Complexes and the Assessment of Their Antityrosinase and Antibacterial Effects

Binuclear silver(I) and copper(I) complexes, 1 and 5, with bridging diphenylphosphine ligands were prepared. In 1, the silver(I) center is located inside a trigonal plane composed of three phosphorus donors from three separate and bridging dppm ligands. The fourth coordination site is filled with neighboring silver(I) ions. The short Ag···Ag distance, as a result of small bite angles from bridging dppm ligands, was determined to be 2.9463(4) Å. In 5, the Cu···Cu distance is 2.915(6) Å, significantly shorter than that observed in comparable structures. Intramolecular hydrogen bonding interactions in these complexes, such as C-H···F, C-H···O, and O-H···F interactions and π···π interactions, played a significant role in the crystal packing and stability of these molecules in the solid state. Derivatization of 1 and 5 using selected sulfur donor dialkyldithiophosphates gave six novel heteroleptic binuclear complexes. Single crystal X-ray diffraction studies of five of these complexes revealed interesting structural features, including strong metallophilic interactions in 1 and 5 and multiple intramolecular and intermolecular hydrogen bonding interactions. The antibacterial activities of complexes 1, 2, 3, 7, and 8 were also screened against gram-positive (Staphylococcus aureus PTCC 1112) and gram-negative (Escherichia coli PTCC 1330) bacteria. Antityrosinase and hemolytic effects of the selected compounds were also determined. Time-dependent density functional theory (TD-DFT), interaction region indicator (IRI), and fuzzy atom bond order (FBO) analyses of the selected complexes provided insights into the electronic and structural characteristics of the metal complexes.

High-Temperature Solid-State Post-Synthetic Modification of Highly Luminescent Cu(I) Metallacycles toward New Luminescent Thermic Tracers

A new luminescent Cu(I) tetrametallic metallacycle B is reported that features very rare semi-bridging aqua ligands. When heated markedly above room temperature, this compound undergoes a post-synthetic transformation in the solid-state, affording the new luminescent metallacycle C. Thermogravimetric analysis, IR spectroscopy and single-crystal X-ray diffraction reveal that this alteration preserves the gross tetrametallic macrocycle structure, but is caused by the release of the coordinated water molecules with the concomitant formation of cuprophilic interactions. This transition induces a shift from eye-perceived green (B) to blue (C) room-temperature luminescence for these molecular solids. Photophysical measurements and time-dependent density-functional theory calculations have been conducted to identify the origins of the emission properties lying in these structurally related assemblies, and suggest that thermally activated delayed fluorescence dominates the radiative relaxation pathways. This study highlights the innovative feature of Cu(I) derivatives, offering access to stimuli-sensitive materials that can witness, a posteriori, the exceeding of critical temperatures in their environment.

Assembling Di- and Polynuclear Cu(I) Complexes with Rigid Thioxanthone-Based Ligands: Structures, Reactivity, and Photoluminescence

Thioxanthone (TX) molecules and their derivatives are well-known photoactive compounds. Yet, there exist only a handful of luminescent systems combining TX with transition metals. Recently, we reported a TX-based PSP pincer ligand (L1) that appears as a promising platform for filling this niche. Herein, we demonstrate that with Cu(I) this ligand exclusively assembles into dimeric structures with either di- or polynuclear Cu(I) cores. With cationic Cu(I) precursors, complexes featuring solvent-bridged bis-cationic cores were obtained. These coordinatively unsaturated bimetallic systems showed surprisingly facile activation of the chloroform C-Cl bonds, suggesting a possible metal-metal cooperation. The reaction of L1 with binary Cu(I) halides afforded dimeric complexes with polynuclear [CuX]n (n = 3 or 4) cores. With X = Br or I, emissive complexes containing stairstep [CuX]4 clusters were obtained. Emission lifetimes in the microsecond range measured for these complexes were indicative of a triplet emission (phosphorescence), which according to our time-dependent density functional theory study originates from a halide-metal-to-ligand charge transfer between the [CuX]4 cluster and the TX backbone of L1. Finally, the distinctive polynucleating behavior of L1 toward Cu(I) was also showcased by a comparison to another PSP ligand with a diaryl thioether backbone (L2), which formed only mononuclear pincer-type complexes, lacking any unusual reactivity or photoluminescence.

Bipyridyl Functionalized NHC-Sulfenyl, Selenenyl Cations; Potential Species for Alkylation Reactions and Ligands in Copper(I) Catalysis

Reactions of bipyridyl-functionalized imidazole-thiones and selones with MeX (X=I, OTf) afforded sulfenyl and selenenyl cations [(NNC)EMe]X (2/3, E=S, Se). Further reactions of these main-group cations with [Cu(CH3CN)4]BF4, Cu(OTf) furnished dicationic [{Cu(μ-I)(NNC)EMe}2][Y]2 (5/6, Y=BF4, OTf) and tricationic copper(I) complexes [Cu{(NNC)EMe}2](OTf)2BF4 (7 a/7 b) when employed [(NNC)EMe]I and [(NNC)EMe]OTf respectively. All these cationic complexes were characterized by various spectroscopic techniques, including X-ray diffraction analysis. The solid-state structures revealed novel bonding modes of the cations. The cationic nature of new complexes was analyzed by the 77Se NMR spectroscopy, which indicated different electronic environments around the selenium centers. The cations [(NNC)EMe]X (X= I, OTf), and (NNC)SMe bearing copper complex [{Cu(μ-I)(NNC)EMe}2][Y]2 proved as potential candidates for alkylation of various Lewis bases and as molecular catalyst in aldehyde-alkyne-amine coupling reactions, respectively. The latter catalytic reactions yielded a range of three-component products in good to excellent yields with low catalyst loading under solvent-free conditions, which demonstrate the potential utility of group-16 cations as ancillary ligands in homogeneous catalysis.

C-H amination chemistry mediated by trinuclear Cu(I) sites supported by a ligand scaffold featuring an arene platform and tetramethylguanidinyl residues

Tripodal ligands that can encapsulate single or multiple metal sites in C3-symmetric geometric configurations constitute valuable targets for novel catalysts. Of particular interest in ligand development are efforts toward incorporating apical elements that exhibit little if any electron donicity, to enhance the electrophilic nature of a trans positioned active oxidant (e.g., metal-oxo, -nitrene). The tripodal ligand TMG3trphen-Arene has been synthesized, featuring an arene platform 1,3,5-substituted with phenylene arms possessing tetramethylguanidinyl (TMG) residues. Compound [(TMG3trphen-Arene)Cu3(μ-Cl)3] has been subsequently synthesized by extracting a Cu3(μ-Cl)3 cluster from anhydrous CuCl and shown to encapsulate a crown-shaped Cu3(μ-Cl)3 fragment, supported by Cu-NTMG bonds and modest Cu3⋯arene long-range contacts. Energy decomposition analysis (EDA) indicates that electrostatic contributions to the total interaction energy far exceed those due to orbital interactions. The latter involve orbital pairings largely associated with the NTMG stabilization of the Cu3(μ-Cl)3 cluster. The independent gradient model based on the Hirshfeld partition (IGMH) corroborates that contacts between the arene platform and the Cu3 triangle are noncovalent in nature. Catalyst [(TMG3trphen-Arene)Cu3(μ-Cl)3] enables amination of sec-benzylic and tert-C-H bonds of a panel of substrates by pre-synthesized PhINTces in solvent matrices that incorporate small amounts of HFIP. The involvement of an electrophilic aminating agent is evidenced by the better yields obtained for electron-rich benzylic sites and is further supported by Hammett analysis that reveals the development of a small positive charge during C-H bond activation. A rather modest KIE effect (2.1) is obtained from intramolecular H(D) competition in the amination of ethylbenzene, at the borderline of reported values for concerted and stepwise C-H amination systems. DFT analysis of the putative copper-nitrene oxidant indicates that the nitrene N atom is bridging between two copper sites in closely spaced triplet (ground state) and broken-symmetry singlet electronic configurations.

Controlling the Size of Molecular Copper Clusters Supported by a Multinucleating Macrocycle

The use of a nonrigid, pyridyldialdimine-derived macrocyclic ligand (3PDAI2) enabled the synthesis of well-defined mono-, di-, tri-, and tetra-nuclear Cu(I) complexes in good yields through rational synthetic means. Starting from mono- and diargentous 3PDAI2 complexes, transmetalation to Cu(I) proceeded smoothly with formation of AgX (X = Cl, I) salts to generate mono-, di-, and trinuclear copper complexes. Monodentate supporting ligands (MeCN, xylNC, PMe3, PPh3) were found to either transmetallate with or bind various di- and trinuclear clusters. The solution-phase dynamic behaviors of these species were studied through NMR spectroscopic investigations, and an in-depth study of the trinuclear systems revealed a rate dependence on the identity of the supporting ligand, indicating that ligand dissociation reactions were involved in the dynamic exchange processes. Synthetic investigations further found methods for the purposeful interconversion between the di- and trinuclear systems as well as the synthesis of a pseudotetrahedral tetracopper complex with two μ-Ph supporting ligands.

Copper Imidazolin-imine Coordination Compounds as Precursors for a Cu/Al Complex

The reactions of [(CF3SO3Cu)2(C6H6)] with the sterically hindered imidazolin-2-imine ligands DippImTMS (1,3-Bis(2,6-diisopropylphenyl)-2-(trimethylsilylimino)imidazoline) or DippImH (1,3-bis(2,6-diisopropylphenyl) imidazolin-2-imine) lead to the formation of the linear copper(I) complexes [Cu(DippImTMS)(OTf)] (1) and [Cu(DippImH)2][OTf] (2), respectively. The triflate counteranion in 2 can be easily exchanged to the weakly coordinating [BArF] giving [Cu(DippImH)2][BArF] (3) (BArF = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate). Substitution of the N-heterocyclic imine (NHI) ligand in 3 by AlCp* (Cp* = pentamethylcyclopentadienyl) gives the tetrahedral [Cu(AlCp*)4][BArF] (5). The reaction between lithiated imidazolin-2-iminate DippImLi and CuCl results in the triangular cluster [Cu3(DippIm)2Cl] (4). All products have been fully characterized by 1H- and 13C NMR, mass spectrometry, as well as SC-XRD.

1D p-type molecular-based coordination polymer semiconductor with ultrahigh mobility

One-dimensional (1D) semiconductor nanostructures exhibit exceptional performance in mitigating short-channel effects and ensuring low power consumption. However, the scarcity of high-mobility p-type 1D materials impedes further advancement. Molecular-based materials offer high designability in structure and properties, making them a promising candidate for 1D p-type semiconductor materials. A molecular-based 1D p-type material was developed under the guidance of coordination chemistry. Cu-HT (HT is the abbreviation of p-hydroxy thiophenol) combines the merits of highly orbital overlap between Cu and S, fully covered surface modification with phenol functional groups, and unique cuprophilic (Cu-Cu) interactions. As such, Cu-HT has a remarkable hole mobility of 27.2 cm2 V-1 s-1, which is one of the highest reported values for 1D molecular-based materials to date and even surpass those of commonly used amorphous silicon as well as the majority of 1D inorganic materials. This achievement underscores the significant potential of coordination polymers in optimizing carrier transport and represents a major advancement in the synthesis of high-performance, 1D p-type semiconductor materials.

Cuprophilic Interactions in Polymeric [Cu10O2(Mes)6]n

The properties of cuprophilic compounds and the underlying fundamental principles responsible for the Cu(I)···Cu(I) interactions have been the subject of intense research as their diverse structural and physical attributes are being explored. In this light, we performed a new study of the compound [Cu10O2(Mes)6] reported by Haakansson et al. using state of the art experimental and theoretical analysis techniques. Doing this, we found the compound to be a polymer in the solid state, best written as [Cu10O2(Mes)6]n, with unsupported Cu(I)···Cu(I) contacts linking the monomers (2.776 Å). The monomeric unit also exhibits various cuprophilic contacts bridged by mesityl and/or oxo ligands. The compound was analyzed in its solid state, revealing luminescent properties resulting from two distinct fluorescent emissions, as well as in solution, in which its polymeric structure reversibly decomposes. A quantum theory of atoms in molecules (QTAIM) analysis based on density functional theory (DFT) calculations allows to characterize the various Cu(I)···Cu(I) contacts, in which only a few, and not necessarily the shortest, are associated with a bond critical point. Additionally, an energy decomposition analysis of the bonding between monomers indicates that it is dominated by dispersion forces in which the ligands play a dominant role, resulting in bonding energies significantly larger than found in previous DFT investigations based on less bulky models.

Ag+-Induced Supramolecular Polymers of Folic Acid: Reinforced by External Kosmotropic Anions Exhibiting Salting Out

Introducing kosmotropic salts enhances protein stability and reduces solubility by withdrawing water from the protein surface, leading to 'salting out', a phenomenon we have mimicked in supramolecular polymers (SPs). Under the guidance of Ag+, folic acid (FA) self-assembled in water through slipped-stacking and hydrophobic interactions into elongated, robust one-dimensional SPs, resulting in thermo-stable supergels. The SPs exhibited temperature and dilution tolerance, attributed to the stability of the FA-Ag+ complex and its hydrophobic stacking. Importantly, FA-Ag+ SP's stability has been augmented by the kosmotropic anions, such as SO42-, strengthening hydrophobic interactions in the SP, evident from the enhanced J-band, causing improvement of gel's mechanical property. Interestingly, higher kosmotrope concentrations caused a significant decrease in SP's solubility, leading to precipitation of the reinforced SPs─a 'salting out' effect. Conversely, chaotropes like ClO4- slightly destabilized hydrophobic stacking and promoted an extended conformation of individual SP chain with enhanced solubility, resembling a 'salting in' effect.

Ultralow thermal conductivity and thermally-deactivated electrical transport in a 1D silver array with alternating δ-bonds

We report the synthesis of a (TMA)AgBr2 (TMA = tetramethylammonium) crystal, which comprises inorganic anionic chains of -(AgBr2)∝- stabilized by columnar stacks of organic TMA cations with a periodic arrangement of shorter and longer Ag(i)⋯Ag(i) bonds, even though all the Ag(i) ions are chemically equivalent. The presence of two chemically non-equivalent bridging Br ions is attributed to the primary cause of such an unusual arrangement, as clearly visualized in the charge density plot of (TMA)AgBr2 extracted from the theoretical calculations based on density functional theory. Remarkably, we identified from the orbital-projected density of states the existence of alternate δ-like bonding involving d xy orbitals of 4d10 Ag(i), which was attributed to the cause for ultralow thermal conductivity and thermally-deactivated electrical transport in (TMA)AgBr2. Barring the energetics, our observations on the existence of a δ-bond will shed new light in understanding the nature of metal-metal chemical bonding and its unprecedented implications.

Lewis Acid-Base Pairs: The Bonding Rule of Closed-Shell M···M' Interactions (M = HgII/PdII; M' = AgI/AuI)

Metallophilic interactions are the widespread interactions in multimetal clusters to orientate closed-shell metal self-assembly form linear, facet, or block clusters. The closed-shell metal cation does not have empty valence orbitals, but is able to attract each other. It is still a conundrum to understand the resource in balancing the strong Coulomb repulsion between two cations. Most traditional descriptions attribute the counterintuitive attractions to London dispersion, Pauli repulsions, and ambiguous orbital interactions. However, neither the dispersion nor the unsourced donor-acceptor interaction can be applied to explain the saturability and directionality in multimetal clusters, where the M···M' structure is the basic molecular unit. Here, we clarify the origination of the covalency in closed-shell metallophilic interactions based on the study of heterobimetallic compounds composed of d10-d8 species (AgI/AuI-PdII) and d10-d10 species (AgI/AuI-HgII) obtained from experiments. The inner d electrons not only participate in the metallophilic interactions but also show different Lewis acidity and basicity in the formation of M···M' structures. The present work not only provides us a novel covalent perspective to visualize the closed-shell M···M' interactions but also unveils the truth of metallophilic interactions.

Electrocatalytic nitrogen reduction to ammonia by atomically precise Cu6 nanoclusters supported on graphene oxide

The electrocatalytic nitrogen reduction reaction (NRR) enables the production of ammonia by the use of renewable energy, providing a direct method for nitrogen fixation. Nevertheless, the NRR process under ambient conditions is often impeded by inertness of N2 and the occurrence of hydrogen evolution as a byproduct in aqueous electrolytes, resulting in a diminished reaction rate and reduced efficiency. In this study, we synthesized Cu6(SMPP)6 nanoclusters (Cu6 NCs for short) and immobilized them on graphene oxide (GO) to investigate their electrocatalytic nitrogen reduction reaction (ENRR) using an H-cell setup. The GO-supported Cu6 NCs exhibit enhanced catalysis with a high NH3 yield rate of 4.8 μg h-1 cm-2 and a high faradaic efficiency up to 30.39% at -1.1 V. Quantum chemistry calculations reveal that the Cu6S6 cluster on GO support facilitates the N2 adsorption and NN bond activation with a surmountable energy barrier for the potential-determining step (N2* → NNH*).

Steric and electronic influence on Cu-Cu short contacts in β-thioketiminato tricopper(I) clusters

A series of β-thioketiminate copper(I) complex trimers [LCuI]3 were synthesized by modifying the ligand framework with electron-withdrawing groups (F and Cl) or electron-donating groups (iPr and Me) at the N-aryl ring as well as with CF3 groups on the chelating backbone. This ligand modification significantly impacts the enhancement of Cu⋯Cu short contacts, which can be rationalized by using steric and electronic factors of the chelated ligand. We observed that this intramolecular cuprophilicity among [LCuI]3 complexes is primarily governed by the size of N-aryl ortho-substituents. These findings were well supported by X-ray crystallography, Raman spectroscopy, and Mayer bond order analysis. The electronic effects induced by the ligand modification on the LCuI fragment were investigated using CO and 2,4,6-CNC6H2Me3 as probe molecules. Corroborated by the FTIR and CV measurements, our results reveal that the β-thioketiminate SN chelators induce more pronounced changes in the electronic character of the LCuI fragment due to the presence of CF3 groups on the chelating backbone in comparison with the F or Cl substituents on the N-aryl ring.

Luminescent Tetranuclear Copper(I) and Gold(I) Heterobimetallic Complexes: A Phosphine Acetylide Amidinate Orthogonal Ligand Framework for Selective Complexation

The synthesis of phosphine acetylide amidinate stabilized copper(I) and gold(I) heterobimetallic complexes was achieved by reacting ligand [{Ph2PC≡CC(NDipp)2}Li(thf)3] (Dipp=2,6-N,N'-diisopropylphenyl) with CuCl and Au(tht))Cl, yielding the eight membered ring [{Ph2PC≡CC(NDipp)2}2Cu2] and the twelve membered ring [{Ph2PC≡CC(NDipp)2}2Au2]. {Ph2PC≡CC(NDipp)2}2Cu2] features a Cu2 unit, which is bridged by two amidinate ligands, served as a metalloligand to synthesize the heterobimetallic CuI/AuI complexes [{(AuX)Ph2PC≡CC(NDipp)2}2Cu2] (X=Cl, C6F5). In these reactions, the central ring structure is retained. In contrast, when the twelve membered ring [{Ph2PC≡CC(NDipp)2}2Au2] was reacted with CuX (X=Cl, Br, I and Mes), the reaction led to the rearrangement of the central ring structure to give [{(AuX)Ph2PC≡CC(NDipp)2}2Cu2] (X=Cl, Br, I and Mes), which feature the same the eight membered Cu2 ring as above. These compounds were also synthesized by a one-pot reaction. The luminescent heterobimetallic complexes were further investigated for their photophysical properties.

Sulfide-Induced Dimerization Versus Demetallation of Tricopper(I) Clusters Protected by Tris-Thiolato Metalloligands

Here, we report the reactivity of copper(I) clusters toward sulfide ions; these sulfide copper(I) clusters have attracted much attention due to their relevance to biologically active centers and their fascinating structural and photophysical properties. Treatment of the CuI 3RhIII 2 pentanuclear complex, [Cu3{Rh(aet)3}2]3+ (aet=2-aminoethanethiolate), in which a {CuI 3}3+ cluster moiety is bound by two fac-[Rh(aet)3] metalloligands, with NaSH in water produced the CuI 6RhIII 4 decanuclear complex, [Cu6S{Rh(aet)3}4]4+, accompanied by the dimerization of [Cu3{Rh(aet)3}2]3+ and the incorporation of a sulfide ion at the center. While similar treatment using the analogous CuI 3IrIII 2 complex with fac-[Ir(aet)3] metalloligands, [Cu3{Ir(aet)3}2]3+, produced the isostructural CuI 6IrIII 4 decanuclear complex, [Cu6S{Ir(aet)3}4]4+, the use of the CuI 3RhIII 2 complex with fac-[Rh(apt)3] metalloligands, [Cu3{Rh(apt)3}2]3+ (apt=3-aminopropanethiolate), resulted in the removal of one of the three CuI atoms from {CuI 3}3+ to afford the CuI 2RhIII 2 tetranuclear complex, [Cu2{Rh(apt)3}2]2+.

Diborane Reductions of CO2 and CS2 Mediated by Dicopper μ-Boryl Complexes of a Robust Bis(phosphino)-1,8-naphthyridine Ligand

A dinucleating 1,8-naphthyridine ligand featuring fluorene-9,9-diyl-linked phosphino side arms (PNNPFlu) was synthesized and used to obtain the cationic dicopper complexes 2, [(PNNPFlu)Cu2(μ-Ph)][NTf2]; [NTf2] = bis(trifluoromethane)sulfonimide, 6, [(PNNPFlu)Cu2(μ-CCPh)][NTf2], and 3, [(PNNPFlu)Cu2(μ-OtBu)][NTf2]. Complex 3 reacted with diboranes to afford dicopper μ-boryl species (4, with μ-Bcat; cat = catecholate and 5, with μ-Bpin; pin = pinacolate) that are more reactive in C(sp)-H bond activations and toward activations of CO2 and CS2, compared to dicopper μ-boryl complexes supported by a 1,8-naphthyridine-based ligand with di(pyridyl) side arms. The solid-state structures and DFT analysis indicate that the higher reactivities of 4 and 5 relate to changes in the coordination sphere of copper, rather than to perturbations on the Cu-B bonding interactions. Addition of xylyl isocyanide (CNXyl) to 4 gave 7, [(PNNPFlu)Cu2(μ-Bcat)(CNXyl)][NTf2], demonstrating that the lower coordination number at copper is chemically significant. Reactions of 4 and 5 with CO2 yielded the corresponding dicopper borate complexes (8, [(PNNPFlu)Cu2(μ-OBcat)][NTf2]; 9, [(PNNPFlu)Cu2(μ-OBpin)][NTf2]), with 4 demonstrating catalytic reduction in the presence of excess diborane. Related reactions of 4 and 5 with CS2 provided insertion products 10, {[(PNNPFlu)Cu2]2[μ-S2C(Bcat)2]}[NTf2]2, and 11, [(PNNPFlu)Cu2(μ,κ2-S2CBpin)][NTf2], respectively. These products feature Cu-S-C-B linkages analogous to those of proposed CO2 insertion intermediate.

Diverse structural reactivity patterns of a POCOP ligand with coinage metals

We have utilised the 4,6-di-tert-butyl resorcinol bis(diphenylphosphinite) (POCOP) ligand for exploring its coordination ability towards group 11 metal centres. The treatment of the bidentate ligand 1 with various coinage metal precursors afforded a wide range of structurally diverse complexes 2-12, depending upon the metal precursors used. This furnishes several multinuclear Cu(I) complexes with dimeric (2) and tetrameric cores (3, 4, and 5). The tetrameric stairstep complex 4 shows thermochromic behaviour, whereas the dimeric complex 2 and tetrameric complex 3 show luminescence properties at cryogenic temperatures. Interestingly, the halide substitution reaction of the dimeric complex 2 with KPPh2 produces a unique mixed phosphine-based tetrameric Cu(I) complex, 5. Treatment of the POCOP ligand with [CuBF4(CH3CN)4] in the presence of 2,2'-bipyridine afforded heteroleptic complex 6, consisting of tri- and tetra-coordinated cationic Cu(I) centres. Furthermore, we could also isolate cubane (8) and stairstep (9) complexes of Ag(I). The cationic Au(I) complex (12) was obtained from the dinuclear Au(I) complex of POCOP, 11. Complex 12 revealed the presence of a strong intramolecular aurophilic interaction with an Au⋯Au bond distance of 3.1143(9) Å. Subsequently, the photophysical properties of these complexes have been studied. All the complexes were characterised by single-crystal X-ray diffraction studies, routine NMR techniques, and mass spectroscopy.

Thermally Activated Delayed Fluorescent Binuclear Copper(I) Alkynyl Complexes with Cuprophilic Interactions

Copper(I)-based thermally activated delayed fluorescence (TADF) emitters have been conceived to be promising candidates for display and lighting applications because of their multifarious structures and strong photoluminescence. Herein a string of binuclear Cu(I) complexes bearing pronounced cuprophilic interactions have been designed and synthesized. [Cu2(dppb)2(μ2-η1-C≡C-Ph)2] (1 a) and [Cu2(dppb)2(μ2-η1-C≡C-PPXZ)2] (1 b) display photoluminescence quantum yields of up to 67 % in doped films and solid states via TADF and exhibit reversible bicolor luminescence switching upon mechanical stimuli. Computational studies manifest that the metal-to-ligand charge transfer predominant transitions ensure a small energy splitting (ΔEST) between the lowest singlet (S1) and triplet (T1) excited states and cuprophilic interactions promote the spin-orbit coupling (SOC), favoring the reverse intersystem crossing (RISC) process. This study provides a new strategy for the construction of stimuli-responsive metal-based TADF materials.

Solvent-Mediated Hetero/Homo-Phase Crystallization of Copper Nanoclusters and Superatomic Kernel-Related NIR Phosphorescence

Atomically precise superatomic copper nanoclusters (Cu NCs) have been the subject of immense interest for their intriguing structures and diverse properties; nonetheless, the variable oxidation state of copper ions and complex solvation effects in wet synthesis systems pose significant challenges for comprehending their synthesis and crystallization mechanism. Herein, we present a solvent-mediated approach for the synthesis of two Cu NCs, namely, superatomic Cu26 and pure-Cu(I) Cu16. They initially formed as a hetero-phase and then separated as a homo-phase via modulating binary solvent composition. In situ UV/vis absorption and electrospray ionization mass spectra revealed that the solvent-mediated assembly was determined to be the underlying mechanism of hetero/homo-phase crystallization. Cu26 is a 2-electron superatom with a kernel-shell structure that includes a [Cu20Se12]4- shell and [Cu6]4+ kernel, containing two 1S jellium electrons. Conversely, Cu16 is a pure-Cu(I) Cu/Se nanocluster that features a [Cu16Se6]4+ core protected by extra dimercaptomaleonitrile ligands. Remarkably, Cu26 exhibits unique near-infrared phosphorescence (NIR PH) at 933 nm due to the presence of a superatomic kernel-related charge transfer state (3MM(Cu)CT). Overall, this work not only showcases the hetero/homo-phase crystallization of Cu NCs driven by a solvent-mediated assembly mechanism but also enables the rare occurrence of NIR PH within the 2-electron copper superatom family.

Pseudohalide Ions as Ligands to Tune Architecture and Luminescence of Polymetallic CU(I) Assemblies

The reaction of preassembled Cu(I) bimetallic units {Cu2(dppm)2} and {Cu2(dppa)2} (dppm: bis(diphenylphosphino)methane and dppa: bis(diphenylphosphino)amine) with pseudohalide linkers (azido, dicyanamide, and tricyanomethanide) allows for the quantitative and selective preparation of three discrete tetrametallic metallacycles of formula [Cu4(μ2-dppm)4(N3)2](PF6)2, [Cu4(μ2-dppm)4(N(CN)2)2](PF6)2, and [Cu4(μ2-dppm)4(C(CN)3)4]. To explore further the impact of the linker on the architecture and dimensionality of the molecular edifice, the study was extended to more sophisticated tetradentate cyanocarbanion ligands (tcnsMe-: 2-(methylthio)-1,1,3,3-propanetetracarbonitrile and tcnsEt-: 2-(ethylthio)-1,1,3,3-propanetetracarbonitrile). Three ladder-like one-dimensional coordination polymers and an octametallic metallacycle have been obtained. The careful comparison of the metric and geometrical intramolecular and intermolecular parameters observed in this series of seven derivatives allows for rationalization of their molecular architectures. The subtle balance between the length and steric hindrance of the ligand and the formation of noncovalent interaction networks greatly influences the topology and dimensionality of the resulting assemblies and will be discussed hereafter. The photophysical properties of these seven polymetallic Cu(I) compounds have also been also studied.

Excitonic cuprophilic interactions in one-dimensional hybrid organic-inorganic crystals

The everlasting pursuit of hybrid organic-inorganic lead-free semiconductors has directed the focus towards eco-friendly copper-based systems, perhaps because of the diversity in chemistry, controlling the structure-property relationship. In this work, we report single crystals of a Cu(i) halide-based perovskite-like organic-inorganic hybrid, (TMA)Cu2Br3, (TMA = tetramethylammonium), consisting of unusual one-dimensional inorganic anionic chains of -(Cu2Br3)-, electrostatically stabilized by organic cations, and the Cu(i)-Cu(i) distance of 2.775 Å indicates the possibility of cuprophilic interactions. X-ray photoelectron spectroscopy measurements further confirmed the presence of exclusive Cu(i) in (TMA)Cu2Br3 and electronic structure calculations based on density functional theory suggested a direct bandgap value of 2.50 eV. The crystal device demonstrated an impressive bulk photovoltaic effect due to the emergence of excitonic Cu(i)-Cu(i) interactions, as was clearly visualized in the charge-density plot as well as in the Raman spectroscopic analysis. The single crystals of a silver analogue, (TMA)Ag2Br3, have also been synthesized revealing a Ag(i)-Ag(i) distance of 3.048 Å (signature of an argentophilic interaction). Unlike (TMA)Cu2Br3, where more density of states from Cu compared to Br near the Fermi level was observed, (TMA)Ag2Br3 exhibited the opposite trend, possibly due to variation in the ionic potential influencing the overall bonding scenario.

Coordination Environment Engineering of Metal Centers in Coordination Polymers for Selective Carbon Dioxide Electroreduction toward Multicarbon Products

Electrocatalytic carbon dioxide reduction reaction (CO2RR) toward value-added chemicals/fuels has offered a sustainable strategy to achieve a carbon-neutral energy cycle. However, it remains a great challenge to controllably and precisely regulate the coordination environment of active sites in catalysts for efficient generation of targeted products, especially the multicarbon (C2+) products. Herein we report the coordination environment engineering of metal centers in coordination polymers for efficient electroreduction of CO2 to C2+ products under neutral conditions. Significantly, the Cu coordination polymer with Cu-N2S2 coordination configuration (Cu-N-S) demonstrates superior Faradaic efficiencies of 61.2% and 82.2% for ethylene and C2+ products, respectively, compared to the selective formic acid generation on an analogous polymer with the Cu-I2S2 coordination mode (Cu-I-S). In situ studies reveal the balanced formation of atop and bridge *CO intermediates on Cu-N-S, promoting C-C coupling for C2+ production. Theoretical calculations suggest that coordination environment engineering can induce electronic modulations in Cu active sites, where the d-band center of Cu is upshifted in Cu-N-S with stronger selectivity to the C2+ products. Consequently, Cu-N-S displays a stronger reaction trend toward the generation of C2+ products, while Cu-I-S favors the formation of formic acid due to the suppression of C-C couplings for C2+ pathways with large energy barriers.

Anisotropic Metal-Metal Pauli Repulsion in Polynuclear d10 Metal Clusters

Metallophilicity has been widely considered to be the driving force for self-assembly of closed-shell d10 metal complexes, but this view has been challenged by recent studies showing that metallophilicity in linear d10-d10 dimers is repulsive. This is due to strong metal-metal (M-M') Pauli repulsion (Wan, Q., Proc. Natl. Acad. Sci. U. S. A. 2021, 118, e2019265118). Here, we study M-M' Pauli repulsion in d10 metal clusters. Our results show that M-M' Pauli repulsion in d10 polynuclear clusters is 6-52% weaker than in similar linear d10 complexes due to the anisotropic shape of (n+1)s-nd hybridized orbitals. The overall M-M' interactions in closed-shell d10 polynuclear metal clusters remain repulsive. The effects of coordination geometry, relativistic effects, and the ligand's electronegativity on M-M' Pauli repulsion in polynuclear d10 clusters have been explored. These findings provide valuable guidance for the design and development of ligands and coordination geometries that alleviate M-M' Pauli repulsion in d10 metal cluster systems.

Multistimuli-responsive multicolor solid-state luminescence tuned by NH-dependent switchable hydrogen bonds

Revealing the stimuli-responsive mechanism is the key to the accurate design of stimuli-responsive luminescent materials. We report herein the multistimuli-responsive multicolor solid-state luminescence of a new dicopper(I) complex [{Cu(bpmtzH)}2(μ-dppa)2](ClO4)2 (1), and the multistimuli-responsive mechanism is clarified by investigating its four different solvated compounds 1·2CH3COCH3·2H2O, 1·2DMSO·2H2O, 1·4CH3OH, and 1·4CH2Cl2. It is shown that luminescence mechanochromism is associated with the breakage of the hydrogen bonds of bmptzH-NH with counter-ions such as ClO4- induced by grinding, while luminescence vapochromism is attributable to the breaking and forming of hydrogen bonds of dppa-NH with solvents, such as acetone, dimethylsulfoxide, and methanol, caused by heating and vapor fuming. In addition, those results might provide new insights into the design and synthesis of multistimuli-responsive multicolor luminescent materials by using various structure-sensitive functional groups, such as distinct N-H ones, to construct switchable hydrogen bonds.

Ferrocene: an exotic building block for supramolecular assemblies

Ferrocene (Fc), a classical organometallic complex, has found potential applications in ligand design, catalysis, and analytical, biological, medicinal and materials chemistry. In recent years, the use of Fc as a building block in supramolecular chemistry has emerged. The molecular shape, size, and hydrophobicity of Fc make it an ideal guest for a variety of macrocyclic host molecules to form stable host-guest complexes. The vertical distance (3.3 Å) between two cyclopentadienyl rings and molecular "ball bearing" property in Fc support the formation of intramolecular π-π stacking, H-bonding and metallophilic interactions between two appropriate substituents in 1,n'-disubstituted ferrocenes. Along with these molecular features, the rigidity along with rotational flexibility, redox reversibility and oxidation-triggered tunable hydrophobicity of Fc have led to its use as an exotic building block for the development of a wide range of supramolecular assemblies such as smart molecular receptors, intricate metal-organic assemblies, supramolecular polymers, and gels including out-of-equilibrium assemblies and metal nanoparticle assemblies. This review highlights the concepts behind the design and development of these assemblies, where the Fc unit has a direct and defined role in their formation and function. The use of Fc in supramolecular assembly is still a relatively young field and set to be the subject of increasing research interest towards the development of fascinating supramolecular structures with tailored properties and programmable functions towards applications in materials and biological sciences.

Thermal/Redox-triggered release of pyrazinic functional molecules by coordination polymers with luminescence monitoring ability

Storage of volatile active molecules, along with the prolongation of their specific functions, requires the use of regulatable carriers. Pyrazine derivatives are highly volatile compounds with a broad application owing to their flavoring, pharmaceutical, antimicrobial, antiseptic, and insecticidal properties. In this study, pyrazines were stored by coordinating them with cuprous iodide to easily generate a series of luminescent coordination polymer (CP)-based carriers. The CPs could respond to thermal-redox stimuli and manipulate pyrazine release by breaking the labile Cu-N bonds when triggered by the two stimuli. Moreover, the release process could be visualized by decreased luminescence caused by the gradual decomposition of CP structures. The loading efficiencies ranged from 31% to 38%, and the controlled release behaviors accord with the zero-order kinetics. This work is the first to prove that CPs could function as dual stimuli-mediated delivery systems, which hold the potential to control the release and strengthen the usability of functional molecules.

Filling the gap with a bulky diaryl boron group: fluorinated and non-fluorinated copper pyrazolates fitted with a dimesityl boron moiety on the backbone

Successful synthesis has been reported of 4-Mes2B-3,5-(CF3)2PzH and 4-Mes2B-3,5-(CF3)2PzH bearing sterically demanding diarylboron moieties at the pyrazole ring 4-position, and their corresponding copper(I) pyrazolate complexes. They show visible blue photoluminescence in solution. The X-ray crystal structures revealed that the fluorinated {[4-BMes2-3,5-(CF3)2Pz]Cu}3 crystallizes as discrete trinuclear molecules whereas as the non-fluorinated {[4-BMes2-3,5-(CH3)2Pz]Cu}3 forms dimers of trimers with two close inter-trimer Cu⋯Cu separations. The solid {[4-BMes2-3,5-(CF3)2Pz]Cu}3 featuring a sterically confined Cu3N6 core displays bright blue phosphorescence while {[4-BMes2-3,5-(CH3)2Pz]Cu}3, which is a dimer of a trimer, is a red phosphor at room temperature. This work illustrates the modulation of photo-physical properties of metal pyrazolates by adjusting the supporting ligand steric features and introducing secondary diarylboron luminophores. Computational analysis of the structures and photophysical properties of copper complexes are also presented.

Dicationic copper(I) complexes bearing ENE (E = S, Se) pincer ligands; catalytic applications in regioselective cyclization of 1,6-diynes

Two novel dicationic binuclear Cu(I) complexes of the type [{(BPPP)E2}Cu]2[BF4]2 (E = S (3a); Se (3b)) bearing (BPPP)E2 (BPPP = bis(diphenylphosphino)pyridine) pincer systems were isolated, and structurally characterized. The solid-state structures of 3a/3b display the presence of intermolecular cuprophilic (Cu⋯Cu) interactions between the two monocationic species, and consist of weak Cu⋯S bonding between the two cations. Besides, complex 3a was introduced as a molecular copper(I) catalyst in cyclization reactions, and new protocols were developed for the synthesis of a series of new oxazole and triazole derivatives bearing alkyne-phenyl propargylic ether substituents. 3a was also found to be active in achieving these two classes of heterocyclic compounds by the mechanical grinding method. One of the key intermediate copper-azide species was detected by the high-resolution mass spectrometry technique, which supports the proposed catalytic pathway. All the reported transformations were accomplished sustainably by employing a well-defined, earth-abundant, and cheap copper(I) catalytic system.

Tetracopper σ-Bound μ-Acetylide and -Diyne Units Stabilized by a Naphthyridine-based Dinucleating Ligand

Reactions of a dicopper(I) tert-butoxide complex with alkynes possessing boryl or silyl capping groups resulted in formation of unprecedented tetracopper(I) μ-acetylide/diyne complexes that were characterized by NMR and UV/Vis spectroscopy, mass spectrometry and single-crystal X-ray diffraction. These compounds possess an unusual μ4 -η1 :η1 :η1 :η1 coordination mode for the bridging organic fragment, enforced by the rigid and dinucleating nature of the ligand utilized. Thus, the central π system remains unperturbed and accessible for subsequent reactivity and modification. This has been corroborated by addition of a fifth copper atom, giving rise to a pentacopper acetylide complex. This work may provide a new approach by which metal-metal cooperativity can be exploited in the transformation of acetylide and diyne groups to a variety of substrates, or as a starting point for the controlled synthesis of copper(I) alkyne-containing clusters.

Crystal structure and synthesis of the bis(anthracene)dicuprate dianion as the dipotassium salt, [K(tetrahydrofuran)2]2[{Cu(9,10-η2-anthracene)}2], the first anionic arene complex of copper

Reactions of (tricyclohexylphosphane)copper(I) chloride with two equivalents of potassium anthracene (KAn) in tetrahydrofuran (THF) at 200 K provides air-sensitive but thermally stable (at 293 K) solutions from which yellow crystalline blocks of bis[bis(tetrahydrofuran-κO)potassium] bis(μ-anthracene-κ2C9:C10)dicopper, [K(THF)2]2[{Cu(9,10-η2-C14H10)}2] or [K(C4H8O)2]2[Cu2(C14H10)2], 1, were isolated in about 50% yield. Single-crystal X-ray crystallographic analysis of 1 confirmed the presence of the first known (arene)cuprate. Also, unlike all previously known homoleptic (anthracene)metallates of d-block elements, which contain metals coordinated only to terminal rings, the organocuprate unit in 1 contains copper bound to the 9,10-carbons of the central ring of anthracene. No other d- or f-block metal is known to afford an anthracene or other aromatic hydrocarbon complex having the architecture of organodicuprate 1.

Synthesis of a chiral dinuclear Cu(II)-benzothiazolamine complex: evidence of cuprophilic interaction in its structure and exploration of its electrochemical properties and catalytic performance

The synthesis of a chiral dinuclear [Cu(OAc)2(L1)]2 complex (A) and its analogues Cu(OAc)2(L1)2 (B), Cu(OAc)2(L1)PPh3 (C), CuBr(L1)PPh3 (D), and Cu(OAc)2(L2) (E) is described. The X-ray structure of A reveals a cuprophilic interaction (2.65 Å) and shows that L1 behaves as a monodentate ligand. The stereogenic centre in L1 aligns the NH group to form non-covalent interactions with the paddle-wheel acetate groups at variable distances (2.4-2.5 Å and 2.2-2.7 Å). Thermogravimetric analysis confirmed our hypothesis that two equivalents of L1 (B) or a combination of L1 and PPh3 (C) would disrupt the cuprophilic interaction. All complexes, except D, showed irreversible redox waves by cyclic voltammetry. Complexes C and E have lower oxidative peaks (at 10 V s-1) than complex A between +0.40 and +0.60 V. This highlights the influence of ligand(s) on the redox behaviour of Cu(II) complexes. The significance of this electrochemical behaviour was evident in the Chan-Lam (CL) coupling reaction, where 2.5 mol% of A successfully facilitated the formation of a C-N bond. This study showcased the structure, thermal stability, electrochemical properties and catalytic performance of a chiral dinuclear copper(II)-benzothiazolamine complex.

Solvatochromic behaviour of cyclic dithioether-functionalized triphenylamine ligands and their mechano-responsive Cu(I) coordination polymers

Cu(I)-based coordination polymers (CPs) are known as efficient emissive materials providing an eco-friendly and cost-effective platform for the development of various functional materials and sensors. In addition to the nature of the metal center, organic ligands also play a crucial role in controlling the emissive properties of coordination polymers. Herein, we report on the synthesis of dithiane- and dithiolane-substituted triphenylamine ligands L1 and L2. These ligands were found to be emissive both in the solid state and in solution. In addition, these ligands exhibit solvatochromic behaviour due to the twisted intramolecular charge transfer (TICT) phenomenon. Next, coordination behaviour of these ligands was explored with Cu(I)X salts (X = Br and Cl) and four new 1D coordination polymers [{Cu(μ2-X)2Cu}(μ2-L)]n, CP1 (X = Br, L = L1), CP2 (X = Cl, L = L1), CP3 (X = Br, L = L2), and CP4 (X = Cl, L = L2) were synthesized and crystallographically characterized. The emission behaviour of all the CPs suggests ligand-centered transitions. On mechanical grinding, emission maxima (λem) for CP1 and CP2 were blue-shifted, whereas for CP3 and CP4 red-shifts were observed. All CPs were found to emit at 448 nm with increased intensity after grinding. It is supposed that grinding is responsible for a change in the spatial arrangement (dihedral angles) of the phenyl groups of triphenylamine, causing the observed emission shifts. Furthermore, the higher emission intensity after grinding suggests the occurrence of a similar phenomenon as an aggregation-induced quenching in these CPs.

Self-Assembly of an Anionic [Cu5I8]3- Supramolecular Cluster Driven by Ion-Pair Interaction and Catalytic Properties

The rational design and controlling synthesis of an anionic cuprous iodide supramolecular cluster with high nuclearity through noncovalent interactions remains a significant challenge. Herein, a cationic organic ligand (L1)3+ was driven by anion-cation ion-pair electrostatic interaction to induce free cuprous iodide to aggregate into an anionic supramolecular cluster, [(Cu5I8)3-(L1)3+] (C1). Moreover, five copper(I) atoms bind with eight iodides through multiply bridged Cu-I bonds associated with intramolecular cuprophilic interactions in this butterfly-shaped cluster core. Supramolecular cluster C1 exhibited a solid-state emission at 380 nm and an emission at 405 nm in acetonitrile at room temperature, respectively. Interestingly, this unprecedented cuprous iodide cluster demonstrated a good catalytic performance for azide-alkyne cycloaddition reaction (CuAAC) and the catalytic yield can be up to 80% for eight different substrates at 80 °C. Furthermore, the density functional theory (DFT) calculation revealed that the thermodynamic-dependent cycloaddition reaction underwent a four-step pathway with an overall energy barrier of -43.6 kcal mol-1 on the basis of intermediates monitored by mass spectrum.

Mixed-Valence Tetrametallic Iridium Chains

Neutral [X-{Ir2 }-{Ir2 }-X] (X=Cl, Br, SCN, I) and dicationic [L-{Ir2 }-{Ir2 }-L]2+ (L=MeCN, Me2 CO) tetrametallic iridium chains made by connecting two dinuclear {Ir2 } units ({Ir2 }=[Ir2 (μ-OPy)2 (CO)4 ], OPy=2-pyridonate) by an iridium-iridium bond are described. The complexes exhibit fractional averaged oxidation states of +1.5 and electronic delocalization along the metallic chain. While the axial ligands do not significantly affect the metal-metal bond lengths, the metallic chain has a significant impact on the iridium-L/X bond distances. The complexes show free rotation around the unsupported iridium-iridium bond in solution, with a low-energy transition state for the chloride chain. The absorption spectra of these complexes show characteristic bands at 438-504 nm, which can be fine-tuned by varying the terminal capping ligands.

Robust and highly emissive copper(I) halide 1D-coordination polymers with triphenylarsine and a series of bridging N-heteroaromatic co-ligands

Various 1D-coordination polymers with dinuclear rhombic {Cu2X2} cores (X = Br, I) were synthesized using a spontaneous evaporation method employing triphenylarsine (AsPh3) and six types of bidentate N-heteroaromatic co-ligands. The coordination polymers exhibited intense emission even at 298 K (quantum yield: up to 0.60), and their emission color was dependent on the N-heteroaromatic co-ligand. The emission efficiencies of these coordination polymers were higher than those of the discrete complexes with AsPh3 and monodentate N-heteroaromatic co-ligands reported in our previous work. In addition, the luminescence of these coordination polymers was more resistant to mechanical stimuli than that of the discrete ones.

Acute Bite Angle POP- and PSP-Type Ligands and Their Trinuclear Copper(I) Complexes: Synthesis and Photo-Luminescence Properties

In the current work, the rational synthesis of trinuclear copper complexes, incorporating acute bite angle POP- and PSP-type ligands, is reported. The in situ formation of POP (Ph2P-O-PPh2) or PSP (Ph2P-S-PPh2) ligands in the presence of a copper(I) precursor gave access to various trinuclear copper complexes of the form [Cu3(μ3-Hal)2(μ-PXP)3]PF6 [X = O; Hal = Cl (1), Br (2), I (3) and X = S; Hal = Cl (5), Br (6), I (7)]. Related iodide-containing complexes and clusters, such as [Cu4(μ3-I)4(Ph2PI)4] (4) and [Cu3(μ3-I)2(μ-I)(μ-PSP)2] (8), could also be obtained via the variation of the reaction stoichiometry. The investigation of the photo-optical properties by photo-luminescence spectroscopy has demonstrated that the phosphorescence in the visible region can be switched off through the mere change of the heteroatom in the ligand backbone (POP vs PSP ligand scaffold). Theoretical studies have been conducted to complement the experimental photo-optical data with detailed insights into the occurring electronic transitions. Consequently, this systematic study paves the way for tuning the photo-optical properties of transition metal complexes in a more rational way.

N-Heterocyclic Carbene Copper (I) Complexes Incorporating Pyrene Chromophore: Synthesis, Crystal Structure, and Luminescent Properties

Luminescent N-heterocyclic carbene chloride copper (I) complexes incorporating pyrene chromophore (1-Pyrenyl-NHC-R)-Cu-Cl, (3, 4) have been prepared and fully characterized. Two complexes were prepared with R = methyl (3) and R = naphthyl groups (4) at the nitrogen center of the carbene unit to tune their electronic properties. The molecular structures of 3 and 4 have been elucidated by X-ray diffraction and confirm the formation of the target compounds. Preliminary results reveal that all compounds including the imidazole-pyrenyl ligand 1 are emissive in the blue region at room temperature in solution and in solid-state. All complexes display quantum yields comparable or higher when compared to the parent pyrene molecule. Interestingly replacement of the methyl by naphthyl group increases the quantum yield by almost two-folds. These compounds might show promise for applications as optical displays.

Eight-Electron Superatomic Cu31 Nanocluster with Chiral Kernel and NIR-II Emission

Owing to the inherent instability caused by the low Cu(I)/Cu(0) half-cell reduction potential, Cu(0)-containing copper nanoclusters are quite uncommon in comparison to their Ag and Au congeners. Here, a novel eight-electron superatomic copper nanocluster [Cu₃₁(4-MeO-PhC≡C)₂₁(dppe)₃](ClO₄)₂ (Cu₃₁, dppe = 1,2-bis(diphenylphosphino)ethane) is presented with total structural characterization. The structural determination reveals that Cu₃₁ features an inherent chiral metal core arising from the helical arrangement of two sets of three Cu₂ units encircling the icosahedral Cu₁₃ core, which is further shielded by 4-MeO-PhC≡C^- and dppe ligands. Cu₃₁ is the first copper nanocluster carrying eight free electrons, which is further corroborated by electrospray ionization mass spectrometry, X-ray photoelectron spectroscopy and density functional theory calculations. Interestingly, Cu₃₁ demonstrates the first near-infrared (750-950 nm, NIR-I) window absorption and the second near-infrared (1000-1700 nm, NIR-II) window emission, which is exceptional in the copper nanocluster family and endows it with great potential in biological applications. Of note, the 4-methoxy groups providing close contacts with neighboring clusters are crucial for the cluster formation and crystallization, while 2-methoxyphenylacetylene leads only to copper hydride clusters, Cu₆H or Cu₃₂H₁₄. This research not only showcases a new member of copper superatoms but also exemplifies that copper nanoclusters, which are nonluminous in the visible range may emit luminescence in the deep NIR region.