The Front Cover shows the course of a stream in which 2-naphthol is converted to a quinone intermediate by a bis(μ-oxido) complex. Subsequent condensation with 1,2-phenylendiamine results in benzo[a]phenazine working as an antimicrobial protective shield for the contaminated lake the stream is crossing on its way to the sea. Thanks to the antimicrobial function of the phenazine, the lower stream is protected from the contamination of plant diseases carrying soil bacteria flowing into the lake from a crop field. More information can be found in the Research Article by S. Herres-Pawlis and co-workers.

The Cover Feature shows a watercolor painting of highly stable copper phosphonate frameworks. These frameworks are created by utilizing a tetrahedral-shaped organic building block called methane tetra-p-phenylphosphonic acid, along with different N-ancillary ligands. The main goal of this study is to optimize the binding modes of the ligands on the copper coordination sphere, resulting in the formation of novel secondary building units (SBUs) in metal organophosphonates. More information can be found in the Research Article by Y. Zorlu, G. Yücesan, and co-workers.

Li-S batteries (LSBs) are considered as the attractive candidates for next-generation high-energy system due to their high energy and low cost. However, their practical application is hindered by several stubborn issues, including the poor electric conductivity of sulfur cathodes, the shuttle of lithium polysulfides (LiPSs) and the slow dynamics during charge/discharge cycles. Transitional iron (Fe)-based compounds are regarded as effectively electrocatalysts for polysulfide conversion by accelerating the reaction kinetics and enhancing the electric conductivity electron/charge transfer. In this study, we investigate the typical transition Fe-based compounds (Fe3X, X = B, C, N) known for their high catalytic ability and analyze their roles as sulfur host for LSBs using density functional theory (DFT). Our finding reveal that Fe3C and Fe3B surfaces exhibit more Fe-S bonds compared to Fe3N surface, which explains the different electrochemical behaviors observed during battery testing with sulfur cathode. Additionally, Fe3N demonstrates greater structural stability and effective polysulfide adsorption according to DFT calculations, outperforming the other two compounds in these aspects. We believe that this theoretical investigation will guide the identification of highly efficient hosts for sulfur cathodes and open new avenues for sulfur host selection in LSBs.

BICAAC (bicyclic (alkyl)(amino)carbene) as ambiphilic carbene has been utilized to prepare stable neutral tetrahydrodiborane [BICAAC→(H2)B-B(H2)←BICAAC] and dihydrodiborene [BICAAC→(H)B=B(H)←BICAAC] compounds. The Lewis base stabilized dihydrodiborene is isoelectronic and isolobal to conventional olefins and therefore offers the possibility to explore the formation of π-complexes with transition metals. Reaction of the diborene with coinage metal salts (CuCl, AgBr and CuI) leads to the formation of π-diborene metal complexes via η2 side-on coordination. These are first examples of dihydrodiborene coinage metal complexes. Interestingly, coordination of two CuCl units to the diborene has been observed for the first time with a considerable lengthening of >B=B< and B-CBICAAC bonds manifesting the key role of the BICAAC combined with small steric requirements of hydride substituents in stabilizing these complexes. The energy decomposition analysis (EDA) calculations reveal the interaction between the diborene and Cu(I)/Ag(I) is mainly electrostatic in nature.

The Front Cover shows the utilization of benzimidazole-derivatized ligands and their mononuclear iron(III) complexes as a viable alternative for hydrolyzing organophosphate pesticides and also to evaluate the second coordination sphere effect of the benzimidazole moieties. Organophosphates are widely employed in safeguarding crops against pests and insects. However, due to their inherent toxicity, catalysts become imperative to facilitate their efficient degradation. The manuscript explores the investigation of the catalytic role played by benzimidazole groups, employing a comprehensive approach that encompasses experimental facets, as well as computational methods like DFT calculations. The findings skillfully strike a balance between the incorporation of aromatic-nucleophilic groups within the second coordination sphere and the optimization of side chain length in order to augment phosphoesterase activity. More information can be found in the Research Article by F. R. Xavier, R. A. Peralta, and co-workers.

The Cover Feature shows a carbonyl trialkyl borate, R₃B-CO, where three consecutive B-to-C alkyl group migrations are indicated by coloured (greenish, blue and violet) arrows, the last two being accompanied by the corresponding (blue and violet) arrows signaling the subsequent inverse (C-to-B) oxygen shift. This represents the consecutive formation of the formal acyl borane, boraepoxide and alkyl boron oxide intermediates resulting from the treatment of trialkyl boranes with carbon monoxide. The art work was designed by Pablo Espinosa Sánchez-Campillo. More information can be found in the Research Article by A. Espinosa Ferao.

[H₃O][NbF₆] was synthesized and characterized. At room temperature, it adopts a polar structure with the dipole momentum of the [H₃O]⁺ ions directed along the polar axis. A phase transition at 363 K leads to a plastic high-temperature polymorph hinting towards potential ferroelectric properties of the compound as the [H₃O]⁺ and [NbF₆]⁻ ions are able to rotate freely. A second phase transition at 137 K leads to a cubic non-centrosymmetric low-temperature polymorph.

Abstract

[H₃O][NbF₆] was obtained from the controlled hydrolysis of NbF₅ in anhydrous liquid HF. It adopts a polar, orthorhombic crystal structure with space group Iba2 (no. 45, oI88) at room temperature. A first-order phase transition at 137 K leads to a cubic non-centrosymmetric polymorph in space group I2₁3 (no. 199, cI88). This low-temperature modification results from a distinct rotation of the [H₃O]⁺ cations canceling their polar orientation in the room temperature phase. Quantum-chemical calculations estimate a rotational barrier between 5.8 to 6.4 kJ/mol. At a temperature of 363 K, the compound adopts a centrosymmetric, cubic crystal structure in space group Pm m (no. 221, cP11) that shows rotational disorder of cations and anions. The transition from the polar phase at room temperature to the centrosymmetric phase at high temperature not only reveals the plastic nature of the high-temperature structure but also hints at potential ferroelectric properties, underscoring the multifaceted behavior of [H₃O][NbF₆] across different temperature regimes.

The influence of the NHC backbone substitution was investigated for palladium-NHC complexes containing axial chirality. The two new series of atropisomeric Pd(NHC) complexes enabled the introduction of bulky moieties as ortho substituents of N-aryl groups. After resolution by chiral HPLC at preparative scale, enantiopure complexes successfully catalyzed the α-arylation of amides (up 96 % ee).

Abstract

In order to facilitate the synthesis of NHC precursors as well as to incorporate new moieties, the influence of the NHC backbone substitution was investigated within the concept of atropisomeric NHC-metal complexes. A series of NHC precursors was prepared from new anilines and used to synthesize the corresponding Pd(allyl)Cl(NHC) complexes, most of the time as a mixture of diastereomers (meso and chiral). Chiral HPLC at preparative scale enabled to obtain enantiopure complexes in low to excellent yields. These complexes displayed good activity in the intramolecular α-arylation of amides and, as a function of the structure of the chiral catalyst, excellent enantioselectivities were reached (up to 96 % ee).

Cerium(III) complexes with redox-active ligands in oxidation states L¹⁻ and L²⁻ have been synthesized and fully characterized. Multielectron movement has been achieved by redox chemistry at the ligands. Sequestering counterions also introduces exciting reactivity, forming Ce(IV) species with dioxygen and oxidative addition of hexamethyldisiloxane to form a bis(siloxide) cerium(IV) species.

Abstract

A family of cerium complexes featuring a redox-active ligand in different oxidation states has been synthesized, including the the iminosemiquinone (isq)¹⁻ compound, Ce(^dippisq)₃ (1-Ceisq), and the amidophenolate (ap)²⁻ species Ce^III(^dippap)₃K₃ (2-Ceap), [Ce^III(^dippap)₃K][K(18-c-6)]₂ (2-Ceap 18c6), and [Ce^III(^dippap)₃K][K(15-c-5)₂]₂ (2-Ceap 15c5). Treating 2-Ceap 15c5 with dioxogen furnishes the cerium(IV) derivative [Ce^IV(^dippap)₃][K(15-c-5)₂]₂ (3-Ceap 15c5), and an analogous synthesis can be used to generate [Ce^IV(^dippap)₃][K(crypt)]₂ (3-Ceap crypt). Similarly, addition of hexamethyldisiloxane produces an interesting bis(amidophenolate) species, [(Me₃SiO)₂Ce^IV(^dippap)₂][K(15-c-5)₂]₂ (4-CeOSiMe₃ ). Full spectroscopic and structural characterization of each derivative was performed to establish the oxidation states of both the ligands and the cerium ions.

The structures of Eu-EDTA complexes at varying protonation state in aqueous solution are resolved with a combination of molecular dynamics simulations and extended X-ray absorption fine structure measurements.

Abstract

Ethylenediaminetetraacetic acid (EDTA), which has two amine and four carboxylate protonation sites, forms stable complexes with lanthanide ions. This work analyzes the coordination structure, in atomic resolution, of the Eu³⁺ ion complexed with EDTA in all its protonation states in aqueous solution. Eu-EDTA complexes were modeled using classical molecular dynamics (MD) simulations using force field parameters optimized with ab initio molecular dynamics (AIMD) simulations. Structures from the MD simulations were used to predict extended X-ray absorption fine structure (EXAFS) spectra and compared with EXAFS measurements of the Eu³⁺ aqua ion and Eu-EDTA complexes at pH 3 and 11. This work details how Eu-EDTA complex coordination structures change with increasing protonation of the EDTA ligand in the complex, from the tightly bound unprotonated complex to the unbinding of the fully protonated EDTA ligand from the Eu³⁺ ion as both become solvated by water. Agreement between predicted and measured EXAFS spectra supports the findings from simulation.