A Redox‐Active Bridging Ligand to Promote Spin Delocalization,High‐Spin Complexes,and Magnetic Multi‐Switchability

A dinuclear Co^II complex, [Co₂(tphz)(tpy)₂]ⁿ⁺ (n=4, 3 or 2; tphz: tetrapyridophenazine; tpy: terpyridine), has been assembled using the redox‐active and strongly complexing tphz bridging ligand. The magnetic properties of this complex can be tuned from spin‐crossover with T_1/2≈470 K for the pristine compound (n=4) to single‐molecule magnet with an S_T=5/2 spin ground state when once reduced (n=3) to finally a diamagnetic species when twice reduced (n=2). The two successive and reversible reductions are concomitant with an increase of the spin delocalization within the complex, promoting remarkably large magnetic exchange couplings and high‐spin species even at room temperature.     

Diferrocenylmercury‐Bridged Diphosphine: A Chiral,Ambiphilic, and Redox‐Active Bidentate Ligand

A diphosphine chelate ligand with a wide and flexible bite angle, a unique stereochemical environment, and redox‐active and ambiphilic character is reported. Initially generated as its HgCl₂ complex by reaction of 1,2‐fc(PPh₂)(SnMe₃) (fc=ferrocenediyl) with HgCl₂ in acetone, treatment with [n‐Bu₄N]CN readily liberates the free chiral bidentate ligand. An intermolecular ClHg−Cl→Hgfc₂ (2.9929(13) Å) interaction that is unprecedented in ambiphilic ligand chemistry is seen in the solid structure of Hg(fcPPh₂)₂⋅HgCl₂ where the bridging mercury atom acts as a σ‐acceptor. Furthermore, a bis‐[Rh(COD)Cl] complex is introduced, which displays relatively short Rh⋅⋅⋅Hg contacts of 3.4765(5) and 3.4013(1) Å. Wiberg indices of 0.12 are determined for these Rh⋅⋅⋅Hg interactions and an AIM analysis reveals bond paths with an electron density ρ(r) of 1.2×10⁻² and 1.4×10⁻² e/a₀³ at the bond critical points.     

Diferrocenophosphaborin: A Planar‐Chiral,Redox‐Active and Anion‐Responsive Ambiphilic Ligand

A new class of Janus‐like ambiphilic ligands is introduced. The rigid diferrocene backbone in heterocycles 4‐SnP and 4‐BP creates an unprecedented chiral environment as demonstrated by multinuclear NMR and single‐crystal X‐ray studies. In addition, the ligands are redox‐responsive and the Lewis acidic borane moiety in 4‐BP can be exploited to further tune the properties: a clear decrease in the CO stretching frequency of a Vaska‐type Rh^I complex 5‐BP is observed upon addition of fluoride ions. Thus, the Lewis acid and Lewis base sites influence each other and their strength can be modulated by redox chemistry and anion binding.     

Biredox Eutectic Electrolytes Derived from Organic Redox‐Active Molecules: High‐Energy Storage Systems

One promising candidate for high‐energy storage systems is the nonaqueous redox flow battery (NARFB). However, their application is limited by low solubility of redox‐active materials and poor performance at high current density. Reported here is a new strategy, a biredox eutectic, as the sole electrolyte for NARFB to achieve a significantly higher concentration of redox‐active materials and enhance the cell performance. Without other auxiliary solvents, the biredox eutectic electrolyte is formed directly by the molecular interactions between two different redox‐active molecules. Such a unique electrolyte possesses high concentration with low viscosity (3.5 m , for N‐butylphthalimide and 1,1‐dimethylferrocene system) and a relatively high working voltage of 1.8 V, enabling high capacity and energy density of NARFB. The resulting high‐performance NARFB demonstrates that the biredox eutectic based strategy is potentially promising for low‐cost and high‐energy storage systems.     

A Bulky m‐Terphenyl Cyclopentadienyl Ligand and Its Alkali‐Metal Complexes

The synthesis of the new m ‐terphenyl‐substituted cyclopentadienyl ligand precursor 1‐cyclopentadiene‐2,6‐bis(2,4,6‐trimethylphenyl)benzene (Ter^MesCpH) is described. The synthesis proceeds through the reaction of Ter^MesLi with cobaltocenium iodide, followed by oxidation of the intermediate cobalt(I) species to give the corresponding cyclopentadiene as a mixture of isomers. The preparation and spectroscopic properties of the alkali‐metal salts (Li–Cs) is described, as well as structural information obtained by X‐ray diffraction studies for the lithium, potassium, and cesium analogues. Crystallographic data demonstrate the ability of these new ligands to act as monoanionic chelates by forming metal complexes with Cp–M–Ar bonding environments.     

Directed Gas‐Phase Synthesis of Triafulvene under Single‐Collision Conditions

The triafulvene molecule (c‐C₄H₄)—the simplest representative of the fulvene family—has been synthesized for the first time in the gas phase through the reaction of the methylidyne radical (CH) with methylacetylene (CH₃CCH) and allene (H₂CCCH₂) under single‐collision conditions. The experimental and computational data suggest triafulvene is formed by the barrierless cycloaddition of the methylidyne radical to the π‐electron density of either C₃H₄ isomer followed by unimolecular decomposition through elimination of atomic hydrogen from the CH₃ or CH₂ groups of the reactants. The dipole moment of triafulvene of 1.90 D suggests that this molecule could represent a critical tracer of microwave‐inactive allene in cold molecular clouds, thus defining constraints on the largely elusive hydrocarbon chemistry in low‐temperature interstellar environments, such as that of the Taurus Molecular Cloud 1 (TMC‐1).     

Diferrocenylmercury‐Bridged Diphosphine: A Chiral,Ambiphilic, and Redox‐Active Bidentate Ligand

A diphosphine chelate ligand with a wide and flexible bite angle, a unique stereochemical environment, and redox‐active and ambiphilic character is reported. Initially generated as its HgCl₂ complex by reaction of 1,2‐fc(PPh₂)(SnMe₃) (fc=ferrocenediyl) with HgCl₂ in acetone, treatment with [n‐Bu₄N]CN readily liberates the free chiral bidentate ligand. An intermolecular ClHg?Cl→Hgfc₂ (2.9929(13) Å) interaction that is unprecedented in ambiphilic ligand chemistry is seen in the solid structure of Hg(fcPPh₂)₂?HgCl₂ where the bridging mercury atom acts as a σ‐acceptor. Furthermore, a bis‐[Rh(COD)Cl] complex is introduced, which displays relatively short Rh???Hg contacts of 3.4765(5) and 3.4013(1) Å. Wiberg indices of 0.12 are determined for these Rh???Hg interactions and an AIM analysis reveals bond paths with an electron density ρ(r) of 1.2×10^?2 and 1.4×10^?2 e/a₀³ at the bond critical points.     

Diferrocenophosphaborin: A Planar‐Chiral,Redox‐Active and Anion‐Responsive Ambiphilic Ligand

A new class of Janus‐like ambiphilic ligands is introduced. The rigid diferrocene backbone in heterocycles 4‐SnP and 4‐BP creates an unprecedented chiral environment as demonstrated by multinuclear NMR and single‐crystal X‐ray studies. In addition, the ligands are redox‐responsive and the Lewis acidic borane moiety in 4‐BP can be exploited to further tune the properties: a clear decrease in the CO stretching frequency of a Vaska‐type Rh^I complex 5‐BP is observed upon addition of fluoride ions. Thus, the Lewis acid and Lewis base sites influence each other and their strength can be modulated by redox chemistry and anion binding.