Facile interconversion of mesitylcopper into a CuMes-Cu2bis(amidinate) triangle and a tetracuprous Möbius strip

A new flexible bis(amidine) ligand featuring two additional N-donor groups incorporates a defined [CuIMesCu2I]2+ fragment from mesitylcopper into a triangular cluster with a reactive organometallic coordination site. Subtle changes to the reaction protocol result in the formation of an intertwined tetracuprous arrangement that adopts the shape of a Möbius strip.

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.

Non-conventional hydrogen bonding and dispersion forces that support embedding mesitylgold into a tailored bis(amidine) framework

A bis(amidine) ligand operates as a molecular lock for two AuMes fragments. The resulting complex retains a flexible double macrocycle with two non-conventional N-H⋯C_ipso hydrogen bonds and distinct intramolecular dispersion forces. Instead of unfolding of the double-ring structure through bond rupture in solution, a conformational ring inversion is observed.

Hydrogen bonds and dispersion forces serving as molecular locks for tailored Group 11 bis(amidine) complexes

A flexible polydentate bis(amidine) ligand LH2 operates as a molecular lock for various coinage metal fragments and forms the dinuclear complexes [LH2(MCl)2], M = Cu (1), Au (2), the coordination...

Calcium and Magnesium Bis(β-diketiminate) Complexes: Impact of the Alkylene Bridge on Schlenk-Type Rearrangements

Dinuclear heteroleptic alkaline-earth-metal complexes are interesting synthetic targets because the close proximity of two metals allows for cooperative effects. However, these complexes are also prone to undergoing Schlenk-type rearrangements, affording less-active homoleptic complexes. Here we present the metalation of bis(β-diketimine) ligands possessing flexible bridging groups, i.e., 1,2-ethylene, 1,3-propylene, and trans-1,2-cyclohexylene, using calcium and magnesium precursors. Four mononuclear homoleptic calcium complexes were obtained, highlighting the pronounced tendency of calcium to undergo Schlenk-like redistributions. In the case of magnesium, however, the bridging group plays a crucial role, yielding seven dinuclear heteroleptic complexes but also one mononuclear and one dinuclear homoleptic complexes. In addition, a trinuclear mixed heteroleptic-homoleptic magnesium complex, which is a rare example of an intermediate of the Schlenk equilibrium, was isolated.

Synthesis, structure, and catalytic activity of dinuclear aluminium bis(amidinate) and bis(guanidinate) complexes

The ring-opening polymerization grand prix: Bis(amidinate)s outpaced their bis(guanidinate) competitors and won the race, while the drivers’ engines using acidic co-initiators collapsed before take-off.

Ditopic bis(N,N',N'-substituted 1,2-ethanediamine) ligands: synthesis and coordination chemistry

The synthesis of two different types of bis(N,N',N'-substituted 1,2-ethanediamine)s, bridged either through the secondary (type 1) or tertiary (type 2) amine groups is reported. Selected protio-ligands have been applied in subsequent metallation reactions using aluminium, magnesium, tin, and zinc sources allowing to isolate five mononuclear and eight dinuclear complexes. All complexes have been fully characterized and their solid-state structures have been studied by means of single-crystal X-ray diffraction analysis. Nine of the 13 complexes carry reactive alkyl, amide or hydride groups, which indicates their potential as catalysts or supports for (transition) metals.

Magnesium bis(amidinate) and bis(guanidinate) complexes: impact of the ligand backbone and bridging groups on the coordination behaviour

A library of ten dinucleating bis(amidine) and bis(guanidine) ligands, in which the bridging groups, terminal rests, and backbone substituents were systematically altered, has been synthesized and subsequently applied in metallation reactions using three different magnesium sources. Eight Mg complexes could be isolated and fully characterized, and in seven cases their solid-state structure could be determined by means of single crystal X-ray diffraction analysis. The results evidence a versatile coordination behaviour, which ranges from the first dinuclear heteroleptic magnesium iodide complex to dinuclear homoleptic complexes. These findings indicate the crucial impact of both the ligand and the magnesium source not only on the accessibility of well-defined dinuclear complexes but also on the aggregation in solution and in the solid state.

Coordination-Bond-Driven Dissolution-Recrystallization Structural Transformation with the Expansion of Cuprous Halide Aggregate

Metal-organic frameworks (MOFs) with cuprous-halide-aggregates have shown superiority as organic LED (OLED) and semiconductor materials, while engineering MOF flexibility by involving the expansion of cuprous aggregates remains a great challenge. In this particular work, a dissolution-recrystallization structural transformation (DRST) with the dramatic growth of Cu^I-I aggregates, from 2D NJNU-100 to 3D NJNU-101 has been successfully realized. The unsaturated coordination nodes (2-positional nitrogen atoms) in NJNU-100 have been demonstrated to be the driven force for DRST to NJNU-101 via the formation of coordination bonds. The structural transformation process was irreversible and observed with optical microscopy and powder XRD. The expansion of Cu^I-I aggregates was also computational simulated accompanying with the rotation of the neutral tripodal TTTMB ligand (1,3,5-tris(1,2,4-triazol-1-ylmethyl)-2,4,6-trimethylbenzene) and the reduction of Cu^II to Cu^I. Moreover, the intermediate product NJNU-102 was captured by adding the planar molecular anthrancene to shut down the reaction, where only partial 2-positional nitrogen atoms coordinated to the aggregates and the anthrancene was oxidized to anthraquinone. NJNU-102 has further confirmed that DRST involved the breakage and recombination of coordination bonds and the electron transfer. NJNU-100 and NJNU-101 could be applied as semiconductor and OLED materials. This work has provided insights for crystal engineering, especially for the construction of the Cu^I_xX_y aggregates, and illustrated that DRST could be controlled with a rational design (as the unsaturated coordination modes).

Ligands with Two Monoanionic N,N-Binding Sites: Synthesis and Coordination Chemistry

Polytopic ligands have become ubiquitous in coordination chemistry because they grant access to a variety of mono- and polynuclear complexes of transition metals as well as rare-earth and main-group elements. Nitrogen-based ditopic ligands, in which two monoanionic N,N-binding sites are framed within one molecule, are of particular importance and are therefore the primary focus of this review. In detail, bis(amidine)s, bis(guanidine)s, bis(β-diimine)s, bis(aminotroponimine)s, bis(pyrrolimine)s, and miscellaneous bis(N,N-chelating) ligands are reviewed. In addition to the general synthetic protocols, the application of these ligands is discussed along with their coordination chemistry, the multifarious binding modes, and the ability of these ligands to bridge two (or more) metal(loids).

A Small Cationic Organo-Copper Cluster as Thermally Robust Highly Photo- and Electroluminescent Material

Organic light-emitting diodes (OLEDs) are revolutionizing display applications. In this aspect, luminescent complexes of precious metals such as iridium, platinum, or ruthenium still playing a significant role. Emissive compounds of earth-abundant copper with equivalent performance are desired for practical, large-scale applications such as solid-state lighting and displays. Copper(I)-based emitters are well-known to suffer from weak spin-orbit coupling and a high reorganization energy upon photoexcitation. Here we report a cationic organo-copper cluster [Cu₄(PCP)₃]⁺ (PCP = 2,6-(PPh₂)₂C₆H₃) that features suppressed nonradiative decays, giving rise to a robust narrow-band green luminophore with a photoluminescent (PL) efficiency up to 93%. PL decay kinetics corroborated by DFT calculations reveal a complex emission mechanism involving contributions of both thermally activated delayed fluorescence and phosphorescence. This robust compound was solution-processed into a thin film in prototype OLEDs with external quantum efficiency up to 11% and a narrow emission bandwidth (65 nm fwhm).

Ethylene-Bridged Hexadentate Bis(amidines) and Bis(amidinates) with Variable Binding Sites

Hexadentate bis(amidines) form versatile networks of hydrogen bonds both in solid state and solution, as revealed by X-ray crystallography, IR, and NMR spectroscopy. Moreover, the corresponding bis(amidinates) produce blue and green emissions in THF solution. Tethered tetradentate bis(amidines) have emerged in coordination chemistry, enantioselective catalysis, as building blocks for polyfunctional heterocycles, and in photoluminescent materials. The next generation of flexible bis(amidine)/bis(amidinate) platforms with up to six N-donor sites has now been established.

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.

Copper(I) iodide ribbons coordinated with thiourea derivatives

Two products of the reactions of CuI with 1-benzoyl-3-(4-bromophenyl)thiourea and with 1-benzoyl-3-(2-iodophenyl)thiourea have been obtained and characterized, namely poly[[[1-benzoyl-3-(4-bromophenyl)thiourea-κS]-μ₃-iodido-copper(I)] acetone hemisolvate], {[CuI(C₁₄H₁₁BrN₂OS)]·0.5C₃H₆O}_n, and poly[μ₄-iodido-μ₃-iodido-[N-(benzo[d]thiazol-2-yl)benzamide-κN]dicopper(I)], [Cu₂I₂(C₁₄H₁₀N₂OS)]_n. Their structures, determined by single-crystal X-ray diffraction analysis, exhibit different stoichiometries and molecular organizations; however, both compounds are polymeric and possess close Cu...Cu contacts. The first product contains a (CuI)_n double chain supported by the thiourea derivative coordinated via the S atom. In the second case, the ligand undergoes dehalogenation and cyclization to form N-(benzo[d]thiazol-2-yl)benzamide that serves as the N-donor ligand which is connected to both sides of a (CuI)_n quadruple chain. In both hybrid inorganic chains, I atoms bridge three or four Cu atoms. The coordination centres adopt more or less distorted tetrahedral geometries. The structures of the (CuI)_n kernels of the ribbons are similar to fragments of the layers in high-pressure phase V copper(I) iodide. Only weak S...O, C-H...O, C-H...I and π-π interactions hold the ribbons together, allowing the formation of crystals.

Tunable Luminescent Heterometallic Zn2Ln2 Edge-Defective Molecular Cubane with Stimuli-Responsive Properties

Heterometallic Zn₂Ln₂ [Ln = Gd (1), Eu (2), Tb (3), Dy (4)] discrete molecules with edge-defective cubane structure are assembled from a multifunctional fluorescent conjugate ligand and Ln^III/Zn^II mixed-metal ions; they exhibit the tunable luminescence, including ligand-based yellow-green light emission for 1 and 4 and lanthanide-center emission for 2 and 3. The multiple stimuli-responsive photoluminescences were investigated to show a two-step thermal-responsive luminescence increase in the intensity upon cooling and piezochromic luminescence.