Cuprophilic Interactions in and between Molecular Entities

Zwitterionic Bergman cyclization triggered polymerization gives access to metal-graphene nanoribbons using a boron metal couple

With the rapid growth in artificial intelligence, designing high-speed and low-power semiconducting materials is of utmost importance. This investigation provides a theoretical basis to access covalently bonded transition metal-graphene nanoribbon (TM-GNR) hybrid semiconductors whose DFT-computed bandgaps were much narrower than the commonly used pentacene. Systematic optimization of substrates containing remotely placed boryl groups and the transition metals produced the zwitterions via ionic Bergman cyclization (i-BC) and unlocked the polymerization of metal-substituted polyenynes. Aside from i-BC, the subsequent steps were barrierless, which involved structureless transition regions. Multivariate analysis revealed the strong dependence of activation energy and the cyclization mode on the electronic nature of boron and Au(I). Consequently, three regions corresponding to radical Bergman (r-BC), ionic Bergman (i-BC), and ionic Schreiner-Pascal (i-SP) cyclizations were identified. The boundaries between these regions corresponded to the mechanistic shift induced by the three-center-three-electron (3c-3e) hydrogen bond, three-center-four-electron (3c-4e) hydrogen bond, and vacant p-orbital on boron. The ideal combination for cascade polymerization was observed near the boundary between i-BC and i-SP.

Fully Delocalized Mixed-Valent Cu1.5 Cu1.5 Complex: Strong Cu-Cu interaction and Fast Electron Self-Exchange Rate Despite Large Structural Changes

A flexible macrocyclic ligand with two tridentate {CNC} compartments can host two Cu ions in reversibly interconvertible states, Cu^I Cu^I (1) and mixed-valent Cu^1.5 Cu^1.5 (2). They were characterized by XRD and multiple spectroscopic methods, including EPR, UV/Vis absorption and MCD, in combination with TD-DFT and CASSCF calculations. 2 features a short Cu⋅⋅⋅Cu distance (≈2.5 Å; compared to ≈4.0 Å in 1) and a very high delocalization energy of 13 000 cm^-1 , comparable to the mixed-valent state of the biological Cu_A site. Electron self-exchange between 1 and 2 is rapid despite large structural reorganization, and is proposed to proceed via a sequential mechanism involving an active conformer of 1, viz. 1'; the latter has been characterized by XRD. Such electron transfer (ET) process is reminiscent of the conformationally gated ET proposed for biological systems. This redox couple is a unique pair of flexible dicopper complexes, achieving fast electron self-exchange closely related to the function of the Cu_A site.

Metallophilic Interactions Drive Supramolecular Chirality Evolution and Amplify Circularly Polarized Luminescence

Metallophilic interactions, which are ubiquitous among d¹⁰ metal complexes with linear coordination geometries, can direct one-dimensional assembly. However, the ability of these interactions to manipulate chirality at the hierarchical level largely remains unknown. In this work, we unveiled the role of Au···Cu metallophilic interactions in directing the chirality of multicomponent assemblies. N-heterocyclic carbene-Au(I) complexes bearing amino acid residues formed chiral co-assemblies with [CuI₂]^- anions via Au···Cu interactions. These metallophilic interactions changed the molecular packing modes of the co-assembled nanoarchitectures from lamellar to columnar chiral packing. This transformation initiated the emergence, inversion, and evolution of supramolecular chirality, thereby affording helical superstructures, depending on the geometry of building units. In addition, the Au···Cu interactions altered the luminescence properties and induced the emergence and amplification of circularly polarized luminescence. This work, for the first time, revealed the role of Au···Cu metallophilic interactions in modulating supramolecular chirality, paving the way for the construction of functional chiroptical materials based on d¹⁰ metal complexes.

A stable superatomic Cu6(SMPP)6 nanocluster with dual emission

We have synthesized single crystals of a highly stable Cu₆ nanocluster protected by six ligands of 2-mercapto-5-n-propylpyrimidine (SMPP). This Cu₆(SMPP)₆ cluster has a quasi-octahedral superatomic Cu₆ core, with the Cu atoms being protected by both -S- and N-bidentate coordination of the SMPP ligands. Interestingly, each Cu atom is linked with an N atom, while the two neighboring Cu atoms on the same triangular facet are linked by the -S- bridge of the ligand. Single-crystal parsing results show that the altered orientation of the SMPP ligands give rise to three packing modes (named as 1, 2, and 3) of the Cu₆(SMPP)₆ NCs. Apart from the well-organized coordination, this Cu₆(SMPP)₆ nanocluster exhibits superatomic stability with a metallic core of 4 valence electrons (1S²2S²||3S²), enabling to largely balance the interactions between the polynuclear core and delocalized electrons. Interestingly, the Cu₆(SMPP)₆ NCs display dual emissions in both ultraviolet-visible (UV-Vis) and near-infrared (NIR) regions. First-principles calculations well reproduce the experimental spectrum, shedding light on the nature of excitation states and metal-ligand interactions in the Cu₆(SMPP)₆ cluster.

Highly Selective CO2 Electroreduction to C2+ Products over Cu2O-Decorated 2D Metal-Organic Frameworks with Rich Heterogeneous Interfaces

The electroreduction of carbon dioxide into high-value-added products is an effective approach to alleviating the energy crisis and pollution issues. However, there are still significant challenges for multicarbon (C₂₊) product production due to the lack of efficient catalysts with high selectivity. Herein, a Cu-rich electrocatalyst, where Cu₂O nanoparticles are decorated on two-dimensional (2D) Cu-BDC metal-organic frameworks (MOFs) with abundant heterogeneous interfaces, is synthesized for highly selective CO₂ electroreduction into C₂₊ products. A high C₂₊ Faradaic efficiency of 72.1% in an H-type cell and 58.2% in a flow cell are obtained, respectively. The heterogeneous interfaces of Cu₂O/Cu-BDC can optimize the adsorption energy of reaction intermediates during CO₂ electroreduction. An in situ infrared spectroscopy study indicates that the constructed interfaces can maintain the particular distribution of Cu valence states, where the C-C coupling is promoted to efficiently produce C₂₊ products owing to the stabilization of *CHO and *COH intermediates.

Discrete Singular Metallophilic Interaction in Stable Large 12-Membered Binuclear Silver and Gold Metallamacrocycles of Amido-Functionalized Imidazole and 1,2,4-Triazole-Derived N-Heterocyclic Carbenes

Metallophilic interactions were observed in four pairs of 12-membered metallamacrocyclic silver and gold complexes of imidazole-derived N-heterocyclic carbenes (NHCs), [1-(R¹)-3-N-(2,6-di-(R²)-phenylacetamido)-imidazol-2-ylidene]₂M₂ [R¹ = p-MeC₆H₄, R² = Me, M = Ag (1b) and Au (1c); R¹ = Me, R² = i-Pr, M = Ag (2b) and Au (2c); R¹ = Et, R² = i-Pr, M = Ag (3b) and Au (3c)], and a 1,2,4-triazole-derived N-heterocyclic carbene (NHC), [1-(i-Pr)-4-N-(2,6-di-(i-Pr)-phenylacetamido)-1,2,4-triazol-2-ylidene]₂M₂ [M = Ag (4b) and Au (4c)]. The X-ray diffraction, photoluminescence, and computational studies indicate the presence of metallophilic interactions in these complexes, which are significantly influenced by the sterics and the electronics of the N-amido substituents of the NHC ligands. The argentophilic interaction in the silver 1b-4b complexes was stronger than the aurophilic interaction in the gold 1c-4c complexes, with the metallophilic interaction decreasing in the order 4b > 1b > 1c > 4c > 3b > 3c > 2b > 2c. The 1b-4b complexes were synthesized from the corresponding amido-functionalized imidazolium chloride 1a-3a and the 1,2,4-triazolium chloride 4a salts upon treatment with Ag₂O. The reaction of 1b-4b complexes with (Me₂S)AuCl gave the gold 1c-4c complexes.

High-nuclearity and thiol protected core-shell [Cu75(S-Adm)32]2+: distorted octahedra fixed to Cu15 core via strong cuprophilic interactions

Atomically precise nanoclusters have a critical role in understanding the structure-property relationships at the atomic level. Copper nanoclusters have attracted considerable attention, but the synthesis is limited because of susceptibility to oxidation. Herein, we developed a reduction speed controlling method to synthesize [Cu₇₅(S-Adm)₃₂]²⁺ (HS-Adm: 1-Adamantanethiol) nanocluster and reveal the key steps in the nucleation process. Cu₇₅ was first observed and characterized with the following features: (i) composed of a face-centered cubic Cu₁₅ kernel and a Cu₆₀ caged shell including 12 distorted octahedra. (ii) The observation of the shortest Cu-Cu bond (2.166(7) Å) in the Cu nanoclusters, which could result from the distortion of the octahedron. (iii) The sole μ³-S mode of S, which plays two roles as a vertex and bridge atom to connect Cu atoms. This work presents a unique nanoball Cu nanocluster with strong cuprophilic interaction and provides a novel method to expand the family of Cu nanoclusters as well.

AgX-based hybrid coordination polymers: mechanochemical synthesis, structure and luminescence property characterization

Hybrid coordination polymers are interesting for their ability to converge the properties of both inorganic and organic systems in one single compound and recently attention has been focused on silver based hybrid coordination polymers due to their luminescence properties. We searched the CSD to establish the propensity of AgXL (X = Cl^-, Br^- and I^-) with L as an organic ligand to form hybrid coordination polymers. About 800 AgXL structures are deposited in the CSD, with huge structural variability: indeed, it is possible to recognize some structural preferences based on the halide nature. The formation of an inorganic polymeric unit is favoured by iodide but it is also possible with the other halides. This research continues with the synthesis of AgX (X = I^-, Br^-) based coordination polymers with 2-, 3- and 4-picolylamine (n-pica) as ligands. By mechanochemical synthesis five new hybrid coordination polymers and one coordination polymer have been obtained and their structures determined. While [(AgI)(n-pica)]_n are not luminescent, [(AgBr)(n-pica)]_n emit and their profile depends on the crystallinity of the sample.

Fully Tin-Coated Coinage Metal Ions: A Pincer-Type Bis-stannylene Ligand for Exclusive Tetrahedral Complexation

The synthesis of a novel bis-stannylene pincer ligand and its complexation with coinage metals (Cu^I , Ag^I and Au^I ) are described. All coinage metal centres are in tetrahedral coordination environments in the solid state and are exclusively coordinated by four neutral Sn^II donors. ¹¹⁹ Sn NMR provided information about the behaviour in solution. All of the isolated compounds have photoluminescent properties, and these were investigated at low and elevated temperatures. Compared to the free bis-stannylene ligand, coordination to coinage metals led to an increase in the luminescence intensity. The new compounds were investigated in detail through all-electron relativistic density functional theory (DFT) calculations.

2-D Molecular Alloy Ru-M (M = Cu, Ag, and Au) Carbonyl Clusters: Synthesis, Molecular Structure, Catalysis, and Computational Studies

The reactions of [HRu3(CO)11]- (1) with M(I) (M = Cu, Ag, and Au) compounds such as [Cu(CH3CN)4][BF4], AgNO3, and Au(Et2S)Cl afford the 2-D molecular alloy clusters [CuRu6(CO)22]- (2), [AgRu6(CO)22]- (3), and [AuRu5(CO)19]- (4), respectively. The reactions of 2-4 with PPh3 result in mixtures of products, among which [Cu2Ru8(CO)26]2- (5), Ru4(CO)12(CuPPh3)4 (6), Ru4(CO)12(AgPPh3)4 (7), Ru(CO)3(PPh3)2 (8), and HRu3(OH)(CO)7(PPh3)3 (9) have been isolated and characterized. The molecular structures of 2-6 and 9 have been determined by single-crystal X-ray diffraction. The metal-metal bonding within 2-5 has been computationally investigated by density functional theory methods. In addition, the [NEt4]+ salts of 2-4 have been tested as catalyst precursors for transfer hydrogenation on the model substrate 4-fluoroacetophenone using iPrOH as a solvent and a hydrogen source.

Synthesis and reactivity of dinuclear copper(I) pyridine diimine complexes

The reaction of a tethered pyridine diimine (PDI) ligand with copper(I) chloride yielded a μ-chlorido bridged cationic dicopper(I) PDI complex, which is a rare structural motif. The geometric constraint of the ligand is fostering attractive van der Waals interactions between the coplanar pyridine units. This is supported by an Atoms in Molecules (AIM) and NCI (non-covalent interaction) analysis. Reaction with carbon monoxide yields the corresponding mono- and dicarbonyl complexes, which display reversible binding of carbon monoxide. This equilibrium was studied by ¹³C-NMR exchange spectroscopy and complemented by DFT and LNO-CCSD(T) calculations.

Transition metal complexes of the PPO/POP ligand: variable coordination chemistry and photo-luminescence properties

In the current work the tautomeric equilibrium between tetraphenyldiphosphoxane (Ph₂P-O-PPh₂, POP) and tetraphenyldiphosphine monoxide (Ph₂P-P(O)Ph₂, PPO) in the absence and presence of transition metal precursors is investigated. Whereas with hard transition metal ions, such as Fe(II) and Y(III), PPO-type complexes, such as [FeCl₂(PPO)₂] (1) and [YCl₃(THF)₂(PPO)] (2), are formed, softer transition metals ions tend to form so-called coordination stabilised tautomers of the POP ligand form, such as [Cu₂(MeCN)₃(μ₂-POP)₂](PF₆)₂ (3), [Au₂Cl₂(μ₂-POP)] (4), and [Au₂(μ₂-POP)₂](OTf)₂ (5). The photo-optical properties of the PPO- and POP-type transition metal complexes are investigated experimentally using photo-luminescence spectroscopy, whereby the presence of metallophillic interactions was found to play a crucial role. The dinuclear copper complex [Cu₂(MeCN)₃(μ₂-POP)₂](PF₆)₂ (3) shows a very interesting thermochromic behavior and intense photo-luminescence with remarkable phosphoresence lifetimes at 77 K, which can probably be attributed to short intramolecular Cu-Cu distances.

Robust dicopper(i) μ-boryl complexes supported by a dinucleating naphthyridine-based ligand

Copper boryl species have been widely invoked as reactive intermediates in Cu-catalysed C–H borylation reactions, but their isolation and study have been challenging. Use of the robust dinucleating ligand DPFN (2,7-bis(fluoro-di(2-pyridyl)methyl)-1,8-naphthyridine) allowed for the isolation of two very thermally stable dicopper(i) boryl complexes, [(DPFN)Cu₂(μ-Bpin)][NTf₂] (2) and [(DPFN)Cu₂(μ-Bcat)][NTf₂] (4) (pin = 2,3-dimethylbutane-2,3-diol; cat = benzene-1,2-diol). These complexes were prepared by cleavage of the corresponding diborane via reaction with the alkoxide [(DPFN)Cu₂(μ-O^tBu)][NTf₂] (3). Reactivity studies illustrated the exceptional stability of these boryl complexes (thermal stability in solution up to 100 °C) and their role in the activation of C(sp)–H bonds. X-ray diffraction and computational studies provide a detailed description of the bonding and electronic structures in these complexes, and suggest that the dinucleating character of the naphthyridine-based ligand is largely responsible for their remarkable stability.

Cu(i) boryl species have been widely invoked as reactive intermediates in Cu-catalysed C–H borylations, but their isolation has been challenging. In this work, thermally robust dicopper(I) boryl complexes have been synthesized and studied in detail.

Selective coordination of coinage metals using orthogonal ligand scaffolds

Group 11 metal complexes with their ability to form metallophilic interations are widely pursued to develop multifunctional luminescent materials. Heteronuclear coinage metal complexes are promising candidates to tune electronic and optical properties which are not readily accessed by their homometallic congeners. In this review, we present the concept of orthogonal ligands which are rationally designed to access heteronuclear coinage metal complexes and studied in terms of their photophysical properties. Bifunctional ligands containing soft and hard donor atoms have the potential of providing different coordination modes to selectively synthesise heterobimetallic complexes in a predictable manner. This review deals with ligand sets composed of pyridine, bipyridine- or iminopyridine-substituted NHCs featuring C-N coordination modes, phosphine-based N-heterocycles and amidinate ligand scaffolds comprising of P-N functionalities and mixed phosphine-phosphine oxide with P-O donor sites. Therefore, the scope of this perspective is the discussion of heteronuclear coinage metal complexes supported by recently developed bifunctional ligands in terms of their synthesis, coordination geometries and tunability of optical properties when compared to their homometallic analogues.

Aurophilic Interactions Studied by Quantum Crystallography

This is the first use of a wave-function-based crystallographic method to characterize aurophilic interactions from X-ray diffraction data. Theoretical calculations previously suggested the importance of electron correlation and dispersion forces, but no influence of relativistic corrections to the Au...Au interaction energy was found. In this study, we confirm the importance of relativistic corrections in the characterization of aurophilic interactions in addition to electron correlation and dispersion.

Hirshfeld atom refinement was used to characterize aurophilic interactions from X-ray diffraction data. An intermediate closed-shell type of aurophilic interaction with some features of covalency was identified when both electron correlation and relativistic corrections were applied. Relativistic correction changes the electron density distribution more than electron correlation. Relativistic effects strongly dominate the metal core region also in the direction of the noncovalent interactions and all of the valence and bonding regions with regard to the Au···Au interaction.

Self-Assembly of Double-Helical Metallopolymers

Metal-containing polymers, or metallopolymers, have diverse applications in the fields of sensors, catalysis, information storage, optoelectronics, and neuromorphic computing, among other areas. The approach of metal-templated subcomponent self-assembly using dynamic covalent linkages allows complex architectures to be formed with relative synthetic ease. The dynamic nature of the linkages between subunits in these systems facilitates error checking during the assembly process and also provides a route to disassemble the structure, rendering these materials recyclable. This Account summarizes a class of double-helical metallopolymers. These metallopolymers are formed via subcomponent self-assembly and consist of two conjugated helical strands wrapping a linear array of Cu^I centers. Starting from discrete model helicates, we discuss how, through the judicious design of subcomponents, long helical metallopolymers can be obtained and detail their subsequent assembly into nanometer-scale aggregates. Two approaches to generate these helical metallopolymers are compared. We describe methods to govern (i) the length of the metallopolymers, (ii) the relative orientations (head-to-head vs head-to-tail) of the two organic strands, and (iii) the screw-sense of the double helix. Achieving structural control allowed the growth behavior of these systems to be probed. The structure influenced properties in ways that are relevant to specific applications; for example, the length of the metallopolymer determines the color of the light it emits in solution. In the solid state, the ionic nature of these helices renders them useful as both emitters and ionic additives in light-emitting electrochemical cells. Moreover, recent experimental work has clarified the role of the linear array of Cu ions in the transport of charge through these materials. The conductivity displayed by a film of metallopolymer depends upon its history of applied voltage and current, behavior characteristic of a memristor. In addition to the prospective applications already identified, others may be on the horizon, potentially combing stimuli-responsive electronic behavior with the chirality of the helical twist.

Metal-organic framework structures of fused hexagonal motifs with cuprophilic interactions of a triangular Cu(I)3(pyrazolate-benzoate) metallo-linker

The reaction of the N,O-heteroditopic bifunctional ligand 4-(3,5-dimethyl-1H-pyrazol-4-yl)benzoic acid (H2mpba) with Cu(NO3)2·2.5H2O and Zn(NO3)2·4H2O or Zn(CH3COO)2·2H2O in N,N-dimethylformamide (DMF) results in concomitant formation of three bimetallic metal-organic frameworks (MOFs) with...

Metalation of a gold(I) metalloligand with P,C-bridging phosphinoferrocenyl groups enables construction of defined multimetallic arrays

The reactions of gold(I) metalloligand [Au2{µ(P,C)-Ph2Pfc}2], where fc stands for ferrocene-1,1ʹ-diyl, with bare or ligand-stabilised group 11 metal ions open an access to diverse oligometallic clusters stabilised by Au-Au, Au-Ag...

Near-infrared emitting copper(I) complexes with a pyrazolylpyrimidine ligand: exploring relaxation pathways

Mononuclear copper(I) complexes [CuL2]I (1), [CuL2]2[Cu2I4]·2MeCN (2) and [CuL2]PF6 (3) with a new chelating pyrazolylpyrimidine ligand, 2-(3,5-dimethyl-1H-pyrazol-1-yl)-4,6-diphenylpyrimidine (L), were synthesized. In the structures of complex cations [CuL2]+, Cu+ ions coordinate...

Dimeric Copper and Lithium Thiolates: Comparison of Copper Thiolates with Their Lithium Congeners

The direct reactions of the large terphenyl thiols HSAr^iPr4 (Ar^iPr4= -C₆H₃-2,6-(C₆H₃-2,6-iPr₂)₂) and HSAr^iPr6 (Ar^iPr6= -C₆H₃-2,6-(C₆H₂-2,4,6-iPr₃)₂) with stoichiometric amounts of mesitylcopper(I) in THF at ca. 80 °C afforded the first well-characterized dimeric copper thiolato species {CuSAr^iPr4}₂ (1) and {CuSAr^iPr6}₂ (2) with elimination of mesitylene. The complexes 1 and 2 were characterized by NMR and electronic spectroscopy as well as by X-ray crystallography. They have dimeric Cu₂S₂ core structures in which the two copper atoms are bridged by the sulfurs from the thiolato ligands and feature short Cu--Cu distances near 2.4 Å as well as a weak copper-flanking aryl ring interaction from a terphenyl substituent. The structures of the planar Cu₂S₂ cores bear a resemblance to the Cu_A site in nitrous oxide reductase in which two cysteines also bridge two copper atoms. The related dimeric Li₂S₂ structural motif was also observed in the lithium congeners {LiSAr^iPr4}₂ (3) and {LiSAr^iPr6}₂ (4) which were synthesized directly from the thiols and n-BuLi in hexanes. However, despite the very similar effective ionic radii of the Li⁺ (0.59 Å) and Cu⁺ (0.60 Å) ions, the Li--Li structures display very much longer (by more than ca. 0.5 Å) separations than the corresponding Cu--Cu distances in 1 and 2, which may be due to weaker dispersion interactions.

Tricopper Melaminate, a Metal-Organic Framework Containing Dehydrogenated Melamine and Cu-Cu Bonding

Crystals of Cu₃(C₃N₆H₃) are formed by a solid-state reaction of CuCl with melamine to form a layered framework structure with open pores running along the hexagonal axis direction of the P6/mcc structure. The compound contains the hitherto unknown (C₃N₆H₃)^3- ion, assigned as melaminate. Bonding interactions within and between Cu-Cu dumbbells, which connect melaminate ions into layers, are analyzed by density functional theory calculations of the electron localization function and directional Young's modulus. Band structure calculations reveal the material to be a semiconductor with a band gap on the order of 2 eV.

A Fused Poly(truncated rhombic dodecahedron)-Containing 3D Coordination Polymer: A Multifunctional Material with Exceptional Properties

The design of new and inexpensive metal-containing functional materials is of great interest. Herein is reported a unique thermochromic near-IR emitting coordination polymer, 3D-[Cu₈I₈(L1)₂]_n, CP2, which is formed when ArS(CH₂)₄SAr (L1, Ar = 4-C₆H₄OMe) reacts with 2 equiv of CuI in EtCN. In MeCN, CP1 ([Cu₄I₄(L1)(MeCN)₂]_n, consisting of an alternating [-Cu₄I₄-L1-Cu₄I₄-L1-]_n chain where the Cu₄I₄ cubane units bear two metal-bound MeCN molecules, is formed. Heat-driven elimination of these MeCN's in solid CP1 also leads to CP2 through a predisposed organization of the Cu₄I₄ units prone to fusion after MeCN eliminations (i.e., a rare case of template effect). The CP2 structure exhibits parallel 1D-(Cu₈I₈)_n chains, (z-axis; designated 1D-[CuI]_n) as secondary building units (SBU) held together by parallel thioether ligands (x,y-axes), forming a nonporous 3D network. The structure of this 1D-[CuI]_n SBU is unprecedented and consists of a series of fused and twisted open Cu₄I₄ cubanes forming a fused poly(truncated rhombic dodecahedron). Unexpectedly, the compact 3D CP2 exhibits a solid-to-solid phase transition at 100 °C and a hysteresis of ∼20 °C. CP1 emits intensively (298 K: λ_emi = 564 nm; Φ_e = 0.35), whereas CP2 presents a strongly red-shifted weaker emission (298 K: λ_emi ∼ 740 nm, Φ_e < 0.0001). Moreover, CP2, which is stable over long periods of time, exhibits thermochromism where the emission intensity of the near-IR band decreases significantly at the benefit of a ligand-centered phosphorescence at 415 nm. Altogether, these properties listed above make CP2 exceptional. The low-energy singlet and triplet excited states have been assigned to ligand/metal-to-ligand charge transfer based on DFT and TD-DFT computations.

Synthesis of an expanded pincer ligand and its bimetallic coinage metal complexes

An expanded pincer ligand tBu-PONNOP (2,7-bis(di-tert-butylphosphinito)-1,8-naphthyridine) has been synthesised and its coordination to coinage metals has been studied. Bimetallic complexes were produced with metal halide salts of the type [M₂X₂(tBu-PONNOP)] (X = Cl, M = Au, Ag, Cu; X = I, M = Cu) with a varying degree of interaction with the naphthyridyl backbone in the order Au < Ag < Cu. The salts [Ag₂(tBu-PONNOP)₂][BAr^F₄]₂ (Ar^F = 3,5-C₆H₃(CF₃)₂) and [Ag₂(NCMe)₂(tBu-PONNOP)]X₂ (X = BAr^F₄, PF₆) were prepared, which may serve as a source of tBu-PONNOP via transmetallation.

Poly[3-methyl-1,3-oxazolidin-2-iminium[µ3-cyanido-tri-µ2-cyanido-κ9C:N-tricuprate(I)]]

The unexpected formation of an oxazole ring has occurred during synthesis of a copper(I) cyanide network polymer as part of our ongoing studies of the structural chemistry of these networks. Crystals of the title compound were formed during the synthesis of a previously reported CuCN network solid containing protonated N-methylethanolamine and have been characterized by single crystal X-ray structure analysis. The structure shows well-defined oxazole-2-iminium cations sitting in continuous channels along the short a-axis of the crystal in a new three-dimensional copper(I) cyanide polymeric network. Evidently, a reaction has occurred between the cyanide ion and the protonated N-methylethanolamine base.

Unprecedented [d9]Cu[d10]Au coinage bonding interactions in {Cu(NH3)4[Au(CN)2]}+[Au(CN)2]- salt

The X-ray structure of the {Cu(NH₃)₄[Au(CN)₂]}⁺[Au(CN)₂]^- salt is reported showing an unprecedented [d⁹]Cu[d¹⁰]Au coinage bond. The physical nature of the interaction has been studied using DFT calculations, including the quantum theory of atoms-in-molecules, the noncovalent interaction plot and the natural bond orbital analysis, revealing the nucleophilic role of the [d¹⁰]Au metal and the electrophilic role of [d⁹]Cu metal.

Group 11 m-Terphenyl Complexes Featuring Metallophilic Interactions

A series of group 11 m-terphenyl complexes have been synthesized via a metathesis reaction from the iron(II) complexes (2,6-Mes₂C₆H₃)₂Fe and (2,6-Xyl₂C₆H₃)₂Fe (Mes = 2,4,6-Me₃C₆H₂; Xyl = 2,6-Me₂C₆H₃). [2,6-Mes₂C₆H₃M]₂ (1, M = Cu; 2, M = Ag; 6, M = Au) and [2,6-Xyl₂C₆H₃M]₂ (3, M = Cu; 4, M = Ag) are dimeric in the solid state, although different geometries are observed depending on the ligand. These complexes feature short metal-metal distances in the expected range for metallophilic interactions. While 1-4 are readily isolated using this metathetical route, the gold complex 6 is unstable in solution at ambient temperatures and has only been obtained in low yield from the decomposition of (2,6-Mes₂C₆H₃)Au·SMe₂ (5). NMR spectroscopic measurements, including diffusion-ordered spectroscopy, suggest that 1-4 remain dimeric in a benzene-d₆ solution. The metal-metal interactions have been examined computationally using the Quantum Theory of Atoms in Molecules and by an energy decomposition analysis employing natural orbitals for chemical valence.

Dual mechanoluminescence system comprising a solid-state di-copper(I) complex containing N-heterocyclic carbene ligands

A simple N-heterocyclic carbene (NHC) ligand linked to a flexible propylene linker allows the formation of "Cu-Cu"- and "2 Cu"-type geometries inside a molecular framework. The incorporation of two Cu(i) ions in close proximity was observed in the Cu-Cu-type geometry but not in the 2 Cu-type geometry. In this study, the ground-state geometries of solid-state di-copper(i) complexes containing NHC ligands with ethyl substituents were modulated by external stimuli. A crystal with the 2 Cu-type geometry was obtained by the mechanical grinding and heating of a crystal with the Cu-Cu-type geometry, as confirmed by the disappearance of the absorption peak attributed to cuprophilic interaction in the diffuse reflection spectrum. The mechanical grinding of both crystals afforded composite states comprising small crystallites of the corresponding crystalline phases and an amorphous domain. This structural transition was accompanied by tribochromism and chronochromism. The results suggest that these di-copper(i) complexes show promise for the development of stimuli-responsive photoluminescent Cu(i) complexes.

[Cu{SC(O)OiPr}]96: A Giant Self-Assembled Copper(I) Supramolecular Wheel Exhibiting Photoluminescence Tuning and Correlations with Dynamic Solvation and Solventless Synthesis

The hierarchical self-organization of structurally complex high-nuclearity metal clusters with metallosupramolecular wheel architectures that are obtained from the self-assembly of smaller solvated cluster units is rare and unique. Here, we use the potentially heteroditopic monothiocarbonate ligand and demonstrate for the first time the synthesis and structure of a solvated non-cyclic hexadecanuclear cluster [Cu{SC(O)OⁱPr}]₁₆·2THF (1) that can simultaneously desolvate and self-assemble in solution and subsequently form a giant metallaring, [Cu{SC(O)OⁱPr}]₉₆ (2). We also demonstrate a luminescent precursor to cluster (2) can be achieved through a solventless and rapid mechanochemical synthesis. Cluster (2) is the highest nuclearity copper(I) wheel and the largest metal cluster containing a heterodichalcogen (O, S) ligand reported to date. Cluster (2) also exhibits solid-state luminescence with relatively long emission lifetimes at 4.1, 13.9 (μs). The synthetic strategy described here opens new research avenues by replacing solvent molecules in stable {Cu₁₆} clusters with designed building units that can form new hybrid and multifunctional finite supramolecular materials. This finding may lead to the development of novel high-nuclearity materials self-assembled in a facile manner with tunable optical properties.

A Dicopper Nitrenoid by Oxidation of a CuICuI Core: Synthesis, Electronic Structure, and Reactivity

A dicopper nitrenoid complex was prepared by formal oxidative addition of the nitrenoid fragment to a dicopper(I) center by reaction with the iminoiodinane PhINTs (Ts = tosylate). This nitrenoid complex, (DPFN)Cu₂(μ-NTs)[NTf₂]₂ (DPFN = 2,7-bis(fluorodi(2-pyridyl)methyl)-1,8-naphthyridine), is a powerful H atom abstractor that reacts with a range of strong C-H bonds to form a mixed-valence Cu(I)/Cu(II) μ-NHTs amido complex in the first example of a clean H atom transfer to a dicopper nitrenoid core. In line with this reactivity, DFT calculations reveal that the nitrenoid is best described as an iminyl (NR radical anion) complex. The nitrenoid was trapped by the addition of water to form a mixed-donor hydroxo/amido dicopper(II) complex, which was independently obtained by reaction of a Cu₂(μ-OH)₂ complex with an amine through a protonolysis pathway. This mixed-donor complex is an analogue for the proposed intermediate in copper-catalyzed Chan-Evans-Lam coupling, which proceeds via C-X (X = N or O) bond formation. Treatment of the dicopper(II) mixed donor complex with MgPh₂(THF)₂ resulted in generation of a mixture that includes both phenol and a previously reported dicopper(I) bridging phenyl complex, illustrating that both reduction of dicopper(II) to dicopper(I) and concomitant C-X bond formation are feasible.

Multinuclear Ag Clusters Sandwiched by Pt Complex Units: Fluxional Behavior and Chiral-at-Cluster Photoluminescence

Multinuclear Ag clusters sandwiched by Pt complex units were synthesized and characterized by single crystal X-ray diffraction and NMR studies. The sandwich-shaped multinuclear Ag complexes showed two different types of fluxional behavior in solution: rapid slippage of Pt complex units on the Ag₃ core and a reversible demetalation-metalation reaction by the treatment with Cl anion and Ag ion, respectively. The Ag₂ complex obtained by demetalation reaction from the Ag₃ complex displayed U to Z isomerization. These multinuclear Ag complexes showed strong photoluminescence whose properties depended on the existence of Pt→Ag dative bonds. The Ag₃ complex, identified to be "chiral-at-cluster", was optically resolved by the formation of a diastereomeric salt with a chiral anion. The enantiomers show circular dichroism (CD) and circularly polarized luminescence (CPL) properties which is unprecedented for compounds based on a chiral sandwich structure. Theoretical calculations allow to understand their structural features and photophysical properties.

2-(Dimethylamino)phosphinine: A Phosphorus-Containing Aniline Derivative

The yet unknown 2-amino-substituted λ³ ,σ² -phosphinines are phosphorus-containing aniline derivatives. Calculations show that the strong interaction of the π-donating NR₂  group with the aromatic system results in a high π-density at the phosphorus atom. We could now synthesize 2-N(CH₃ )₂ -functionalized phosphinines, starting from a 3-N(CH₃ )₂ -substituted 2-pyrone and (CH₃ )₃ Si-C≡P. Their reaction with CuBr⋅S(CH₃ )₂ affords Cu^I  complexes with the first example of a neutral phosphinine acting as a rare bridging μ₂ -P-4e donor-ligand between two Cu^I  centers. Our experimental and theoretical investigations show that 2-aminophosphinines are missing links in the series of known 2-donor-functionalized phosphinines.

Tris(pentafluoroethyl)difluorophosphorane: A Versatile Fluoride Acceptor for Transition Metal Chemistry

Fluoride abstraction from different types of transition metal fluoride complexes [Ln MF] (M=Ti, Ni, Cu) by the Lewis acid tris(pentafluoroethyl)difluorophosphorane (C2 F5 )3 PF2 to yield cationic transition metal complexes with the tris(pentafluoroethyl)trifluorophosphate counterion (FAP anion, [(C2 F5 )3 PF3 ]- ) is reported. (C2 F5 )3 PF2 reacted with trans-[Ni(iPr2 Im)2 (ArF )F] (iPr2 Im=1,3-diisopropylimidazolin-2-ylidene; ArF =C6 F5 , 1 a; 4-CF3 -C6 F4 , 1 b; 4-C6 F5 -C6 F4 , 1 c) through fluoride transfer to form the complex salts trans-[Ni(iPr2 Im)2 (solv)(ArF )]FAP (2 a-c[solv]; solv=Et2 O, CH2 Cl2 , THF) depending on the reaction medium. In the presence of stronger Lewis bases such as carbenes or PPh3 , solvent coordination was suppressed and the complexes trans-[Ni(iPr2 Im)2 (PPh3 )(C6 F5 )]FAP (trans-2 a[PPh3 ]) and cis-[Ni(iPr2 Im)2 (Dipp2 Im)(C6 F5 )]FAP (cis-2 a[Dipp2 Im]) (Dipp2 Im=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) were isolated. Fluoride abstraction from [(Dipp2 Im)CuF] (3) in CH2 Cl2 or 1,2-difluorobenzene led to the isolation of [{(Dipp2 Im)Cu}2 ]2+ 2 FAP- (4). Subsequent reaction of 4 with PPh3 and different carbenes resulted in the complexes [(Dipp2 Im)Cu(LB)]FAP (5 a-e, LB=Lewis base). In the presence of C6 Me6 , fluoride transfer afforded [(Dipp2 Im)Cu(C6 Me6 )]FAP (5 f), which serves as a source of [(Dipp2 Im)Cu)]+ . Fluoride abstraction of [Cp2 TiF2 ] (7) resulted in the formation of dinuclear [FCp2 Ti(μ-F)TiCp2 F]FAP (8) (Cp=η5 -C5 H5 ) with one terminal fluoride ligand at each titanium atom and an additional bridging fluoride ligand.