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.

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.

Twisted and Disconnected Chains: Flexible Linear Tetracuprous Arrays and a Decanuclear CuI Cluster as Blue- and Green/Yellow-Light Emitters

Defined arrays of transition metal ions embedded in tailored polydentate ligand scaffolds allow for a systematic design of their physical properties. Such molecular strings of closed-shell transition metal centers are particularly interesting for Group 11 metal ions in the oxidation state +1 if they undergo metallophilic d10···d10 contact interactions since these clusters are oftentimes efficient photoluminescence (PL) emitters. Copper is particularly attractive as a sustainable earth-abundant coinage metal source and because of the ability of several CuI complexes to serve as powerful thermally activated delayed fluorescence (TADF) emitters in molecular/organic light-emitting devices (OLEDs). Our combined synthetic, crystallographic, photophysical, and computational study describes a straight tetracuprous array possessing a centrally disconnected CuI2···CuI2 chain and a continuous helically bent CuI4 complex. This molecular helix undergoes a facile rearrangement in diethyl ether solution, yielding an unprecedented nanosized CuI10 cluster (2.9 × 2.0 nm) upon crystallization. All three clusters show either bright blue phosphorescence, TADF, or green/yellow multiband phosphorescence with quantum yields between 6.5 and 67%, which is persistent under hydrostatic pressure up to 30 kbar. Temperature-dependent PL investigations in combination with time-dependent density-functional theory (TD-DFT) calculations and void space analyses of the crystal packings complement a comprehensive correlation between the molecular structures and photoluminescence properties.

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.

Heterometallic bond activation enabled by unsymmetrical ligand scaffolds: bridging the opposites

Heterobi- and multimetallic complexes providing close proximity between several metal centers serve as active species in artificial and enzymatic catalysis, and in model systems, showing unique modes of metal-metal cooperative bond activation. Through the rational design of well-defined, unsymmetrical ligand scaffolds, we create a convenient approach to support the assembly of heterometallic species in a well-defined and site-specific manner, preventing them from scrambling and dissociation. In this perspective, we will outline general strategies for the design of unsymmetrical ligands to support heterobi- and multimetallic complexes that show reactivity in various types of heterometallic cooperative bond activation.

Real-Time Fluorescent Monitoring of Kinetically Controlled Supramolecular Self-Assembly of Atom-Precise Cu8 Nanocluster

Kinetically stable and long-lived intermediates are crucial in monitoring the progress and understanding of supramolecular self-assembly of diverse aggregated structures with collective functions. Herein, the complex dynamics of an atomically precise Cu^I nanocluster [Cu₈ (^t BuC₆ H₄ S)₈ (PPh₃ )₄ ] (Cu8a) is systematically investigated. Remarkably, by monitoring the aggregation-induced emission (AIE) and electron microscopy of the kinetically stable intermediates in real time, the directed self-assembly (DSA) process of Cu8a is deduced. The polymorphism and different emission properties of Cu NCs aggregates were successfully captured, allowing the structure-optical property relationship to be established. More importantly, the utilization of a mathematical "permutation and combination" ideology by introducing a heterogeneous luminescent agent of a carbon dot (CD) to Cu8a aggregates enriches the "visualization" fluorescence window, which offers great potential in real time application for optical sensing of materials.

Tetra- and hexanuclear string complexes of the coinage metals

Reaction of the PNNP ligand system N,N'-bis[(2-diphenylphosphino)phenyl]formamidinate (dpfam) featuring different coordination compartments with [AuCl(tht)], [CuMes]₅, [AgMes]₄, or [AuC₆F₅(tht)] (tht = tetrahydrothiophene) resulted in tetranuclear homo- and heterometallic coinage metal complexes, as well as a hexanuclear gold complex. All of them feature a metal string conformation. Photophysical investigation revealed a significant dependence of the photoluminescence properties on the metal composition. Below 100 K, the PL efficiency of three compounds approaches nearly 100%.

Transition Metal Chain Complexes Supported by Soft Donor Assembling Ligands

The chemistry of discrete molecular chains constituted by metals in low oxidation states, displaying metal-metal proximity and stabilized by suitable metal-bridging, assembling ligands comprising at least one soft donor atom is comprehensively reviewed; complexes with a single (hard or soft) bridging atom (e.g., μ-halide, μ-sulfide, or μ-PR₂ etc.) as well as "closed" metal arrays (that fall in the realm of cluster chemistry) are excluded. The focus is on transition metal-based systems, with few excursions to cases combining transition and post-transition elements. Most relevant supporting ligands have neutral C, P, O, or S donor (mainly, N-heterocyclic carbene, phosphine, ether, thioether) or anionic donor (mainly phenyl, ylide, silyl, phosphide, thiolate) groups. A supporting-ligand-based classification of the metal chains is introduced, using as the classifying parameter the number of "bites" (i.e., ligand bridges) subtending each intermetallic separation. The ligands are further grouped according to the number of donor atoms interacting with the metal chain (called denticity in the following) and the column of the Periodic Table to which the set of donor atoms belongs (in ascending order). A complementary metal-based compilation of the complexes discussed is also provided in a concise tabular form.

Precise Implantation of an Archimedean Ag@Cu12 Cuboctahedron into a Platonic Cu4Bis(diphenylphosphino)hexane6 Tetrahedron

Precision loading of nanoclusters in confined spaces, which has been enthusiastically pursued in the scientific realm, is still associated with some mysteries of "how", "when", and "why". Here, we isolated two similar heterometallic cluster-in-cage compounds, [Ag@Cu₁₂S₈@Cu₄(dpph)₆]X (X = OH, SD/AgCu16a and X = PF₆, SD/AgCu16b; SD = SunDi), by use of an antigalvanic reaction between organometallic [PhC≡CCu]_n and Ph₃CSH with elemental silver. Both compounds are formed by fitting an Archimedean Ag@Cu₁₂ cuboctahedral cluster into a Platonic Cu₄(dpph)₆ tetrahedral cage [dpph = bis(diphenylphosphino)hexane]. The Ag@Cu₁₂ cluster is a hollow cuboctahedral Cu₁₂ cage filled with a central Ag^I atom, and all eight triangular faces of the Ag@Cu₁₂ cuboctahedron are triply capped by eight S^2- ions, four of which in a tetrahedral array further internally pillar four Cu vertices of the outer Cu₄(dpph)₆ tetrahedron, fixing the cluster in the cage. Both compounds can be deemed as molecular fragments excised from porous nanomaterials filled with discrete nanoclusters, thus providing more details for understanding the confined growth of atomically precise nanoclusters. Electrospray ionization mass spectrometry (ESI-MS) reveals that the AgCu₁₆ cluster is quite stable in CH₂Cl₂ and can stepwise lose dpph ligand in the gas phase under increased collision energy. This work not only presents a precise aggregation of metal atoms in a confined cavity to form a cluster-in-cage compound but also provides deep insights into the binding and geometry matching between clusters and cages in one entity.

Efficient Blue Phosphorescence in Gold(I)-Acetylide Functionalized Coinage Metal Bis(amidinate) Complexes

The synthesis of linear symmetric ethynyl- and acetylide-amidinates of the coinage metals is presented. Starting with the desilylation of the complexes [{Me3 SiC≡CC(NDipp)2 }2 M2 ] (Dipp=2,6-diisopropylphenyl) (M=Cu, Au) it is demonstrated that this compound class is suitable to serve as a versatile metalloligand. Deprotonation with n-butyllithium and subsequent salt metathesis reactions yield symmetric tetranuclear gold(I) acetylide complexes of the form [{(PPh3 )AuC≡CC(NDipp)2 }2 M2 ] (M=Cu, Au). The corresponding Ag complex [{(PPh3 )AuC≡CC(NDipp)2 }2 Ag2 ] was obtained by a different route via metal rearrangement. All compounds show bright blue or blue-green microsecond long phosphorescence in the solid state, hence their photophysical properties were thoroughly investigated in a temperature range of 20-295 K. Emission quantum yields of up to 41 % at room temperature were determined. Furthermore, similar emissions with quantum yields of 15 % were observed for the two most brightly luminescent complexes in thf solution.

Dimensionality Expansion of a Butterfly Shaped Pd4 Framework: Constructing Edge-Sharing Pd6 Tetrahedra

The construction of well-defined transition-metal clusters has attracted substantial attention due to their unique chemical and/or physical properties. Metal clusters with 1D or 2D structures are now accessible by template-synthesis methods, in which multiple metal atoms are arranged with the aid of template molecules and their 1D or 2D structures. However, the rational synthesis of 3D clusters remains challenging, mostly due to a lack of appropriate template molecules. Herein, we report the rational synthesis of a 2D butterfly shaped Pd₄ framework (2) and 3D edge-sharing Pd₆ tetrahedra (5) by treatment of easily available organosilicon compounds with Pd(CNtBu)₂ . The diphenylsilylene moiety thereby serves as the key component to generate the butterfly structure of the Pd₄ clusters in 2. A dimensionality expansion, induced by two Cl atoms, of two butterfly shaped Pd₄ subunits supported by two diphenylsilylene moieties afforded the edge-sharing tetrahedral architecture of the Pd₆ cluster in 5.

Linear Copper Complex Arrays as Versatile Molecular Strings: Syntheses, Structures, Luminescence, and Magnetism

The defined linear arrangement of metal atoms in discrete coordination complexes or polymers is still one of the most intriguing challenges in synthetic chemistry. These chain arrangements are of fundamental importance, because of their potential applications as molecular wires and single molecule magnets (SMM) in microelectronic devices on a molecular scale. Oligonuclear Group 11 metal complexes with suitable bridging ligands, specifically those that are based on copper as the first choice of a cheap precursor coinage metal, are of particular interest in this regard. This is due to the superior luminescence properties of these linear clusters that often show d¹⁰ ⋅⋅⋅d¹⁰ interactions in their molecular structures. The combination of Cu^I with heavier coinage metal ions results in tunable emissive arrays that are also stimuli-responsive. Thus, both linear multinuclear Cu^I and linear heteropolymetallic Cu^I /Ag^I as well as Cu^I /Au^I clusters are excellent candidates for applications in molecular/organic light-emitting devices (OLEDs). Alternatively, paramagnetic multinuclear cupric arrays are prominent as potential molecular wires with enhanced magnetic properties through multiple coupled d⁹ centers. This Review covers the whole range of linear multinuclear assemblies of cuprous and cupric ions in complexes and coordination polymers, their syntheses, photophysical behavior, and magnetic properties. Moreover, recent advances in the rapidly progressing field of hetero-Cu^I /Ag^I and Cu^I /Au^I molecular strings are also discussed.

Photo-induced translocation of a Pdn moiety (n = 2, 7) on a conjugated polyene ligand

The Pd₂-translocation on a tetraene ligand is switchable between the thermodynamic equilibrium state and the photo-stationary state. The Pd₇-translocation on a carotene ligand proceeds smoothly under photo-irradiation.

Halide and substituent dependent structural variation in copper(i) halide complexes of 1,5,9-triphosphacyclododecanes

The reactions of 1,5,9-triethyl-1,5,9-triphosphacyclododecane, [12]-ane-P3Et3, and 1,5,9-tri(2-propyl)-1,5,9-triphosphacyclododecane, [12]-ane-P3iPr3 with copper(i)halides produce either bimetallic species of the type [([12]-ane-P3R3)Cu(CuX2)] (X = halide) or monomeric [([12]-ane-P3R3)CuX] depending on the nature of the halide and, to a lesser extent, the macrocycle. With CuCl only bimetallic complexes are formed with one copper centre bound to the macrocycle and a second attached through a Cu-Cu bond with a mono bridging chloride. CuBr affords monomeric [([12]-ane-P3R3)CuBr] complexes when performed in a 1 : 1 M : L ratio whereas the bimetallic compound [([12]-ane-P3Et3)(CuBr)2], resulted when a 2 : 1 ratio of M : L was employed. With CuI in all ratios only monomeric complexes were obtained. The synthesised complexes have been fully characterised by spectroscopic and analytical techniques and by determination of the molecular structures by single-crystal X-ray diffractometry.