The Cover Feature illustrates how a newly obtained dinuclear cobalt complex bearing a novel bipyrazole and tetrazole-based ligand 1′-((1H-tetrazol-5-yl)methyl)-3,5,5′-trimethyl-1′H-1,3′-bipyrazole fights off the fungus Fusarium oxysporum f. sp. Albedinis, represented in blue, which is the main cause of the Bayoud disease responsible for great damage to the palm trees in North Africa. In a fictional boxing match, the dinuclear cobalt metal complex is knocking out the fungi with ease, symbolising the treatment of sick plants, thus yielding healthy palm trees ready to be harvested for dates. The artwork for the cover was done by Olivera Cvetković. More information can be found in the Research Article by Y. Garcia and co-workers.

Two dinuclear pyrazine-bridged rare earth complexes were synthesized through a bridge splitting reaction, and unambiguously characterized by X-ray crystallography, spectroscopy, and computations. The cyclic voltammograms reveal multiple redox features which are attributed to the bridging pyrazine ligand. These materials represent promising building blocks for the development of supramolecular systems.

Abstract

The development of reaction pathways and ancillary ligand scaffolds is essential in the pursuit of higher nuclearity rare earth metal clusters that are relevant in storage materials and catalysis. Guanidinate anions represent attractive ligands due to their high degree of customizability allowing for facile alterations of both their steric and electronic properties. Here, we demonstrate an unprecedented bridge splitting reaction that shifts chloride anions in favor of a bridging neutral pyrazine to give pyrazine-bridged dinuclear guanidinate rare earth complexes, [{(Me₃Si)₂NC(NⁱPr)₂}₂RECl]₂(μ-pyz) (RE =Y (1) and Er (2), pyz=pyrazine). Each six-coordinate metal center is ligated by two guanidinates, one chloride ligand, and one nitrogen atom from the bridging pyrazine unit. The molecules were characterized by X-ray crystallography, IR, NMR, and UV-Vis spectroscopy. DFT calculations conducted on 1 provide insight into both the bonding picture and the mechanism of complex formation. This type of reaction constitutes a seminal application of a bridge splitting mechanism to the rare earth metals.

Despite a wide spatial separation of the magnetic cations, the oxide Sr₃(Ag_2/3Sr_1/6)RuO₆ shows robust antiferromagnetic order below the relatively high Néel temperature of 79 Kelvin in magnetic fields up to at least 9 Tesla. The new oxido-ruthenate(V) was synthesized in a reactive potassium superoxide flux at high temperature.

Abstract

Black, air-stable crystals of the new ruthenate(V) Sr₃(Ag_2/3Sr_1/6)RuO₆ were grown in a silver ampoule using KO₂ as oxidative flux. X-ray diffraction on single-crystals revealed a rhombohedral structure with the space group R c. Sr₃(Ag_2/3Sr_1/6)RuO₆ crystallizes isostructural to Sr₄PtO₆ in the K₄CdCl₆ structure type. By sharing trigonal faces, alternating [RuO₆] octahedra and [(Ag_2/3Sr_1/6□_1/6)O₆ trigonal prisms form segmented chains running parallel to the crystallographic c-axis. Eightfold coordinated strontium cations are located between the rods. Regardless of the wide spatial separation of the magnetic cations (588 and 594 pm), Sr₃(Ag_2/3Sr_1/6)RuO₆ shows long-range antiferromagnetic order below the relatively high Néel temperature of 79 K in magnetic fields up to at least 9 T, as measurements of the magnetic susceptibility and heat capacity show. Despite the pseudo one-dimensional character of the structure, the characteristic of the susceptibility indicates a three-dimensional coupling of magnetic ions.

The fully water-soluble compound [Ru₃O(CH₃COO)₆(4-ampy)₃]Cl (1) engages in a hydrogen-bonds network involving the 4-ampy ligands and methanol, Cl-, and the π-cloud of neighboring 4-ampy molecules. 1 has pK_a=2.25 and logP=−0.86, showing its high hydrophilicity. 1 interacts with HSA by static mechanism through hydrogen-bonds formation, which was confirmed by molecular docking calculations.

Abstract

The water-soluble compound [Ru₃O(CH₃COO)₆(4-ampy)₃]Cl (1, 4-ampy=4-aminopyridine) was evaluated in terms of its biologically relevant properties. Compound 1 participates in a hydrogen bonding network which includes the NH₂ substituents of the ancillary ligands, methanol molecules, the Cl⁻ counter-ion, and a non-conventional hydrogen bond with the neighboring 4-ampy molecules′ π-cloud, as determined by X-ray measurements. One protonation equilibrium was observed at pH values below 2.3. Additionally, the compound exhibited a partition coefficient value of −0.86 (±0.07), indicating that it is highly hydrophilic. At 37 ⁰C and pH=7.4 (phosphate buffer), compound 1 shows moderate (K_sv=2.4 10⁴ M⁻¹) and spontaneous (ΔG=−26.4 kJ mol⁻¹) binding to human serum albumin (HSA) through ground-state association, which involves formation of hydrogen bonds (ΔH=−35.7 kJ mol⁻¹ and, ΔS=−29.8 J mol⁻¹ K⁻¹). Molecular docking calculations support the formation of hydrogen bonds between 1 and HSA, and suggest subdomain IIA (site I), which contains the Trp-214 residue, as the primary interactive pocket, in agreement with the experimental static fluorescence quenching mechanism. Furthermore, a preliminary assay reveals that 1 has low cytotoxicity towards human glioblastoma U87-MG cells.

The hydroarylation of acetylene is catalyzed by dicationic palladium and platinum pincer complexes [M(PNP)(C₂H₄)](SbF₆)₂ (M=Pd and Pt; PNP=2,6-bis(diphenylphosphinomethyl)pyridine). After optimization of reaction conditions, a benchmark of TON 200 is achieved for the catalytic addition of pentamethylbenzene to acetylene with 0.5% [Pd(PNP)(C₂H₄)](SbF₆)₂ at room temperature in 24 h under acid-free conditions. Water in small amounts serves as co-catalyst.

Abstract

Four dicationic palladium and platinum ethylene complexes of the type [M(PNP)(C₂H₄)]X₂ (M=Pd, Pt; X=BF₄, SbF₆, PNP=2,6-bis(diphenylphosphinomethyl)pyridine) were studied as pre-catalysts for the intermolecular hydroarylation of acetylene under acid-free conditions. The palladium complex [Pd(PNP)(C₂H₄)](SbF₆)₂ was found to be the most active catalyst for the addition of pentamethylbenzene to acetylene at room temperature. In a ³¹P NMR spectroscopic study the impact of the counter anion on the rate determining step was demonstrated. Various reaction parameters were screened to optimize the catalytic efficiency. The presence of small amounts of water were beneficial and increased the reaction rate. Water acts as co-catalyst assisting in proton transfer during the catalytic reaction. After optimization of the reaction conditions, a benchmark for the palladium(II) catalyzed hydroarylation of acetylene was achieved with TON 200 at room temperature in 24 h under acid-free conditions. However, this catalytic system has a very limited substrate scope.

Reversibility of a U^VO₂ ⁺/U^VIO₂ ²⁺ redox equilibrium in a [emim]Tf₂N-based liquid electrolyte was successfully established after addition of DMF and Cl⁻ appropriately. The former was employed to reduce viscosity of the system for improving diffusivity of the U-based electrode active materials, while the latter is also essential to stabilize both U^VO₂ ⁺ and U^VIO₂ ²⁺ as tetrachloro complexes.

Abstract

We studied electrochemical behavior of U^VO₂ ⁺/U^VIO₂ ²⁺ in non-aqueous liquid electrolytes to clarify what is required to attain its reversibility for utilizing depleted U in a redox-flow battery. To transfer knowledge from former pyrochemical systems in high temperature molten salts, 1-ethyl-3-methylimidazolium bis(trifluoromethyl)sulfonylamide ([emim]Tf₂N) ionic liquid was employed here. As a result, a reversible redox reaction of the U^VO₂ ⁺/U^VIO₂ ²⁺ was successfully observed on a glassy carbon working electrode under presence of Cl⁻ in [emim]Tf₂N, where [U^VIO₂Cl₄]²⁻+e⁻=[U^VO₂Cl₄]³⁻ occurs after stabilization of both U oxidation states by the Cl⁻ coordination. The observed electrochemical responses are rather sensitive to an electrode material, so that cyclic voltammograms on a Pt working electrode were actually irreversible. To improve diffusivity of solutes, viscosity (η) of [emim]Tf₂N diluted with an auxiliary molecular solvent, N,N-dimethylformamide (DMF), was examined under absence and presence of Cl⁻. When the mole fraction of DMF (x _DMF) is 0.769, η of the mixture becomes sufficiently low to be utilized as a liquid electrolyte. Finally, we have succeeded in demonstrating a reversible redox reaction of [U^VIO₂Cl₄]²⁻+e⁻=[U^VO₂Cl₄]³⁻ in the [emim]Tf₂N-DMF (50 : 50 v/v, x _DMF=0.769) liquid electrolyte containing [Cl⁻]=0.519 M, where η=6.2 mPa ⋅ s.

A family of titanium-oxo clusters were assembled from large-size ligand embonic acid-modified {Ti₂} molecular building blocks under solvothermal conditions and Ti₂₀ with a large nuclear number has been used as a stable and heterogeneous catalyst to catalyze sulfur oxidation reactions efficiently.

Abstract

To design and synthesize high-nucleated titanium-oxo clusters rationally based on molecular building blocks with potential coordination ability is still a great challenge. In this work, a family of titanium-oxo clusters, including Ti₂ , Ti₆ , Ti₁₂ , and Ti₂₀ clusters, have been assembled from large-size ligand embonic acid-modified {Ti₂} molecular building blocks under solvothermal conditions. By modulating auxiliary linkers and solvent types, the {Ti₂} building blocks exhibit varying degrees of polymerization to form high-nuclear titanium-oxo clusters. Notably, Ti₂₀ with high nucleation, as the decamer containing {Ti₂} building blocks, can act as a stable and heterogeneous catalyst to efficiently catalyze the oxidation of sulfides to sulfones and sulfoxides when using H₂O₂ as the green oxidant. This study provides a new approach for the design and synthesis of highly nucleated and homometallic TOCs based on {Ti₂} units.

This work reports the syntheses of two new Cu(II) coordination complexes using cis-1,4 cyclohexanedicarboxylic acid (cis-1,4-H₂chdc) linker; and 4,4′-dimethyl-2,2′-bipyridine (1)/5,5′-dimethyl-2,2′-bipyridine (2) auxiliary ligands, wherein, cis-1,4-chdc adopts chair form in 1 and boat conformation in 2. Intriguingly, this conformational change impacts the DNA binding capacities of the complexes as revealed by spectrophotometry, circular dichroism spectroscopy and docking studies.

Abstract

Two new coordination complexes were synthesized, which are formulated as [Cu₂(cis-1,4-chdc)(4,4′-Me₂bpy)₄] ⋅ 2(ClO₄ ⁻) ⋅ H₂O (1) and [Cu₂(cis-1,4-chdc)(5,5′-Me₂bpy)₄] ⋅ 2(ClO₄ ⁻) ⋅ H₂O (2), using cis-1,4-cyclohexanedicarboxylic acid (cis-1,4-H₂chdc), 4,4′-dimethyl-2,2′-bipyridine (4,4′-Me₂bpy), 5,5′-dimethyl-2,2′-bipyridine (5,5′-Me₂bpy). Interestingly, cis-1,4-chdc adopts chair form in 1 and boat conformation in 2. This conformational change impacts the DNA binding capacities of the complexes as revealed by spectrophotometry, circular dichroism (CD) spectroscopy and docking studies. The complex 1 having the chair conformation shows higher affinity towards the DNA base pairs due to anti-alignment of the planar aromatic pyridyl rings of 4,4′-Me₂bpy, which strongly intercalates with the adenosine base pairs of DNA by formation of three π–π stacking and two extra π-positive stacking interactions between adenosine bases and positively charged nitrogen. Conversely, 5,5′-Me₂bpy with planar aromatic pyridyl rings of complex 2 shows bis-intercalation with weak affinities toward base pairs by formation of two π–π stacking and one π-positive stacking interactions.

Nitrosyl Ruthenium compounds are promising platforms for nitric oxide (NO) delivery. A novel nitrosyl ruthenium complex containing the ligand 2-methylimidazole was synthetized and characterized through spectroscopic techniques, including X-ray Absorption Spectroscopy (XAS). That compound showed promising NO releasing capabilities and promoted vasodilation together with free radical scavenging. Such properties are desirable for the treatments of cardiovascular diseases, such as atherosclerosis.

Abstract

Nitrosyl ruthenium complexes have emerged as promising platforms for the controlled delivery of nitric oxide (NO) and nitroxyl (HNO), both of which possess significant therapeutic implications. Considering this scenario, we synthesized and characterized the metal complex cis-[RuNO(phen)₂(2MIM)]³⁺ and its precursors, where phen and 2MIM correspond to 1,10-phenantroline and 2-methylimidazole, respectively. Comprehensive structural elucidation was undertaken using a combination of spectroscopic and electrochemical methodologies, including XANES/EXAFS experiments. This structural data was further validated through DFT computational analyses. We demonstrated that such compound can release NO and HNO in the presence of thiol-based substrates. Not only this, but the same metal complex can also delivery nitric oxide under irradiation with visible light (λ=460 nm). The nitrosyl complex and its derivatives displayed marked vasodilatory capabilities as evidenced in assays involving isolated rat aorta rings. They also exhibited commendable antioxidant activity in free radical scavenging assays. Collectively, based on these data, this nitrosyl ruthenium compound is a potential therapeutic candidate, especially in the field of cardiovascular pathology like atherosclerosis, thereby deserving further in-depth investigations.

Exploration of the multielectron reduction chemistry of the lanthanide complexes Cp*₂LnCl(bipy), Cp*₂Ln(bipy), and [Cp*₂Ln(bipy)]¹⁻ highlights the unusual reactivity available from this redox-active platform. A variety of unusual polysulfide, polyazide, and mixed-valence complexes are accessible, many of which are formed through the loss of a Cp* ligand and the generation of mono-Cp* complexes.

Abstract

Exploration of the reduction chemistry of the 2,2’-bipyridine (bipy) lanthanide metallocene complexes Cp*₂LnCl(bipy) and Cp*₂Ln(bipy) (Cp* = C₅Me₅) resulted in the isolation of a series of complexes with unusual composition and structure including complexes with a single Cp* ligand, multiple azide ligands, and bipy ligands with close parallel orientations. These results not only reveal new structural types, but they also show the diverse chemistry displayed by this redox-active platform. Treatment of Cp*₂NdCl(bipy) with excess KC₈ resulted in the formation of the mono-Cp* Nd(III) complex, [K(crypt)]₂[Cp*Nd(bipy)₂], 1, as well as [K(crypt)][Cp*₂NdCl₂], 2, and the previously reported [K(crypt)][Cp*₂Nd(bipy)]. A mono-Cp* Lu(III) complex, Cp*Lu(bipy)₂, 3, was also found in an attempt to make Cp*₂Lu(bipy) from LuCl₃, 2 equiv. of KCp*, bipy, and K/KI. Surprisingly, the (bipy)¹⁻ ligands in neighboring molecules in the structure of 3 are oriented in a parallel fashion with intermolecular C⋅⋅⋅C distances of 3.289(4) Å, which are shorter than the sum of van der Waals radii of two carbon atoms, 3.4 Å. Another product with one Cp* ligand per lanthanide was isolated from the reaction of [K(crypt)][Cp*₂Eu(bipy)] with azobenzene, which afforded the dimeric Eu(II) complex, [K(crypt)]₂[Cp*Eu(THF)(PhNNPh)]₂, 4. Attempts to make 4 from the reaction between Cp*₂Eu(THF)₂ and a reduced azobenzene anion generated instead the mixed-valent Eu(III)/Eu(II) complex, [K(crypt)][Cp*Eu(THF)(PhNNPh)]₂, 5, which allows direct comparison with the bimetallic Eu(II) complex 4. Mono-Cp* complexes of Yb(III) are obtained from reactions of the Yb(II) complex, [K(crypt)][Cp*₂Yb(bipy)], with trimethylsilylazide, which afforded the tetra-azido [K(crypt)]₂[Cp*Yb(N₃)₄], 6, or the di-azido complex [K(crypt)]₂[Cp*Yb(N₃)₂(bipy)], 7 a, depending on the reaction stoichiometry. A mono-Cp* Yb(III) complex is also isolated from reaction of [K(crypt)][Cp*₂Yb(bipy)] with elemental sulfur which forms the mixed polysulfido Yb(III) complex [K(crypt)]₂[Cp*Yb(S₄)(S₅)], 8 a. In contrast to these reactions that form mono-Cp* products, reduction of Cp*₂Yb(bipy) with 1 equiv. of KC₈ in the presence of 18-crown-6 resulted in the complete loss of Cp* ligands and the formation of [K(18-c-6)(THF)][Yb(bipy)₄], 9. The (bipy)¹⁻ ligands of 9 are arranged in a parallel orientation, as observed in the structure of 3, except in this case this interaction is intramolecular and involves pairs of ligands bound to the same Yb atom. Attempts to reduce further the Sm(II) (bipy)¹⁻ complex, Cp*₂Sm(bipy) with 2 equiv. of KC₈ in the presence of excess 18-crown-6 led to the isolation of a Sm(III) salt of (bipy)²⁻ with an inverse sandwich Cp* counter-cation and a co-crystallized K(18-c-6)Cp* unit, [K₂(18-c-6)₂Cp*]₂[Cp*₂Sm(bipy)]₂ ⋅ [K(18-c-6)Cp*], 10.