Cover Feature: Formation of Eigen or Zundel Features at Protonated Water Cluster–Aromatic Interfaces (ChemPhysChem 16/2023)

Interfacial interactions of protonated water clusters adsorbed at aromatic surfaces play an important role in biology, and in atmospheric, chemical and materials sciences. Here, we investigate the interaction of protonated water clusters ((H⁺H₂O)_n (where n=1–3)) with benzene (Bz), coronene (Cor) and dodecabenzocoronene (Dbc)). To study the structure, stability and spectral features of these complexes, computations are done using DFT-PBE0(+D3) and SAPT0 methods. These interactions are probed by AIM electron density topography and non-covalent interactions index (NCI) analyses. We suggest that the excess proton plays a crucial role in the stability of these model interfaces through strong inductive effects and the formation of Eigen or Zundel features. Also, computations reveal that the extension of the π-aromatic system and the increase of the number of water molecules in the H-bounded water network led to a strengthening of the interactions between the corresponding aromatic compound and protonated water molecules, except when a Zundel ion is formed. The present findings may serve to understand in-depth the role of proton localized at aqueous medium interacting with large aromatic surfaces such as graphene interacting with acidic liquid water. Besides, we give the IR and UV-Vis spectra of these complexes, which may help for their identification in laboratory.     

Front Cover: Understanding Local-Field Correction Factors in the Framework of the Onsager−Böttcher Model (ChemPhysChem 3/2019)

The determination of the appropriate local-field factor for quantifying the response of a molecule to an external electric field is of major importance in optical spectroscopy. Although numerous studies have dealt with the evolution of the optical properties of emitters as a function of their environment, the choice of the model used to quantify local fields is still ambiguous, and sometimes even arbitrary. In this paper, we review the Onsager–Böttcher model, which introduces the polarizability of the probe molecule as the determinant parameter for the local field factor, and we establish a simple conceptual framework encompassing all commonly used models. Finally, a discussion of published experimental research illustrates the potential of the measurement of local electric fields in dense dielectric media, as well as the subtleties involved in their interpretation.     

Striking Size and Doping Effects of Ti−Si−O Clusters on Methane Conversion Reactions

The size and doping effects in methane activation by Ti−Si−O clusters have been explored by using a combination of gas-phase experiments and quantum chemical calculations. All [Ti_mSi_nO_2(m+n)]^.+ (m+n=2, 3, 8, 10, 12, 14) clusters can extract a hydrogen from methane. The associated energies and structures have been revealed in detail. Moreover, the doping and size effects have been discussed involving generalized Kohn-Sham energy decomposition analysis, natural population analysis, Wiberg bond indexes (WBI), molecular polarity index (MPI) and ionization potential (IP). It suggested that Ti−Si−O clusters with a low Ti : Si ratio is beneficial to adsorbing methane and inclination to the hydrogen atom transfer (HAT) process, while the clusters with a high Ti : Si ratio favors the generation of a terminal oxygen radical and results in high reactivity and turnover frequency. On the other hand, a cluster size of m+n=12 is recommended considering both the ionization potential and the turnover frequency of the reaction. Hopefully, these finding will be instructive for the design of high-performance Ti−Si−O catalyst toward methane conversion.     

Effects of NH 4 + and Cl− on the preparation of nanocrystalline TiO2 by hydrothermal method

Nanocrystalline TiO₂ powders with different morphologies and grain sizes were successfully synthesized by the hydrothermal method. Different concentrations of hydrochloric acid (HCl), ammonium chloride (NH₄Cl), ammonium sulfate [(NH₄)₂SO₄], and ammonium carbonate [(NH₄)₂CO₃] were used as additives in the hydrothermal process to investigate the effect of the concentration of ammonium (NH ₄ ⁺ ) and chloride ions (Cl^?) on the phase compositions, morphologies, and grain sizes of the prepared TiO₂. The as-synthesized samples were characterized by X-ray diffraction (XRD), transmission electron microscopy, Brunauer–Emmett–Teller analysis, and UV–Vis spectra. XRD results show that the as-synthesized powders are composed of anatase or a mixture of anatase and brookite. The grain size of the synthesized nano-TiO₂ powder ranged from 5.0 to 11.3 nm, and the related BET specific surface area varied from 127.5 to 191.0 m²/g. The photocatalytic activities of the prepared TiO₂ powders were evaluated by degradation of methylene blue (MB) in aqueous solution under UV light irradiation, and the results show that the photocatalytic performance of TiO₂ powders synthesized with additives is improved compared with that of TiO₂ prepared without any additives.     

CAS SCF ECP calculations on the optical spectrum of Mo2(O2CH)4 and on the barrier to internal rotation in Mo2Cl84−

The optical spectrum in the near UV region has been calculated for Mo₂(O₂CH)₄ using the CAS SCF method and effective core potential techniques. Assignments for the observed transitions between 20000 and 45000 cm⁻¹ are suggested. The barrier to internal rotation has been calculated for Mo₂Cl₈⁴⁻ and it is concluded that if there is a barrier at all it is very low, a result following a twist of the complex. The theoretical spectra for Mo₂(O₂CH)₄ and Mo₂Cl₈⁴⁻ are compared and discussed. It is suggested that there should exist a weak structure in the electronic spectrum of Mo₂(O₂CH)₄ in the vicinity of 10000 cm⁻¹.     

Cover Feature: Rare Spin Avoided σ-σ Diradical Planar Tetracoordinate Boron Cluster: A Proto-Star for Planar Pentacoordination (ChemPhysChem 18/2023)

We report a global planar star-like cluster B₃Li₃ featuring three planar tetracoordinate boron centres with a rare spin avoided σ-σ diradical character. The cluster was found to be stable towards dissociation into different fragments. The spin density was found to be localized solely on the three boron atoms in the molecular plane. This spin avoided σ-σ diradical character leads to the extension of the coordination number to yield a neutral B₃Li₃H₃ and a cationic B₃Li₃H₃⁺ cluster with three planar pentacoordinate boron centres in their global minimum structures. The planar geometry of the aninonic B₃Li₃H₃⁻ cluster is slightly higher in energy. The planar global clusters were found to maintain planarity in their ligand protected benzene bound complexes, B₃Li₃(Bz)₃, B₃Li₃H₃(Bz)₃ and B₃Li₃H₃(Bz)₃⁺ with high ligand dissociation energies offering candidature for experimental detection.     

Cover Feature: Hg(II)⋅d8[M] Interactions: Are they Metallophilic Interactions or Spodium Bonds? (ChemPhysChem 24/2023)

Some literature reports have shown the existence of short Hg(II)⋅⋅⋅d⁸[M] (M=Pd, Pt) contacts between linear Hg(II) and square planar d⁸[M] complexes that have been defined as heterometallophilic interactions. Linear L−Hg(II)−L complexes exhibit a π-hole or positive belt of electrostatic potential at the Hg atom, whereas late transition metals can serve as effective electron donors through their filled d_z2 orbitals. This study provides compelling evidence that Hg(II)⋅⋅⋅d⁸[M] interactions should be more appropriately termed spodium bonds.     

Front Cover: Synthesis of Substituted Indazole Acetic Acids by N−N Bond Forming Reactions (Eur. J. Org. Chem. 29/2023)

Herein, we report on the discovery and development of novel cascade N−N bond forming reactions for the synthesis of rare indazole acetic acid scaffolds. This approach allows for convenient synthesis of three distinct indazole acetic acid derivatives (unsubstituted, hydroxy, and alkoxy) by heating 3-amino-3-(2-nitroaryl)propanoic acids with an appropriate nucleophile/solvent under basic conditions. The reaction tolerates a range of functional groups and electronic effects and, in total, 23 novel indazole acetic acids were synthesized and characterized. This work offers a valuable strategy for the synthesis of useful scaffolds for drug discovery programs.     

Negative ion photoelectron spectroscopy of N2O− and (N2O)−2

We have recorded the photoelectron spectra of the gas phase negative ions N₂O⁻ and (N₂O)₂⁻ both of which were prepared in a nozzle ion source. The shift between the maxima of the two spectra is interpreted in terms of the dissociation energy of the dimer ion.     

Hydrolysis of Cephanone in SDS/n-C_5H_(11)OH/H_2O System

IntroductionMicellesolutioncomposedofsurfactantscanaffect,adjustandcontrolmanychemicalreactionsaccordingtoitseffectsoflocalconcentration ,polarity ,charge ,microvis cosity,electrostatics ,etc ..1,2 Recently ,ithasarousedmuchattentiontoconductchemicalreactionsusingmi croemulsionasmicroreactor .3 7Theeffectofmicelleonthechemicalreactionstemsfromitsstaticelectricityandhy drophobicity .Usually ,cationicsurfactantcancatalyzethereactionbetweennucleophileandneutralmolecule ,whileanionicsurfactantsusp…     

Stabilization of Pancake Bonding in (TCNQ)2.− Dimers in the Radical-Anionic Salt (N−CH3−2-NH2−5Cl−Py)(TCNQ)(CH3CN) Solvate and Antiferromagnetism Induction

We report a new antiferromagnetic radical-anion salt (RAS) formed from 7,7,8,8-tetracyanquinonedimethane (TCNQ) anion and 2-amino-5-chloro-pyridine cation with the composition of (N−CH₃−2-NH₂−5Cl−Py)(TCNQ)(CH₃CN). The crystallographic data indicates the formation of (TCNQ)₂^.− radical-anion π-dimers in the synthesized RAS. Unrestricted density functional theory calculations show that the formed π-dimers characterize with strong π-stacking “pancake” interactions, resulting in high electronic coupling, enabling efficient charge transfer properties, but π-dimers cannot be stable in the isolated conditions as a result of strong Coulomb repulsions. In a crystal, where (TCNQ)₂^.− π-dimers bound in the endless chainlets via supramolecular bonds with (N−CH₃−2-NH₂−5-Cl−Py)⁺ cations, the repulsion forces are screened, allowing for specific parallel π-stacking interactions and stable radical-anion dimers formation. Measurements of magnetic susceptibility and magnetization confirm antiferromagnetic properties of RAS, what is in line with the higher stability of ground singlet state of the radical-anion pair, calculated by means of the DFT. Therefore, the reported radical-anion (N−CH₃−2-NH₂−5Cl−Py)(TCNQ)(CH₃CN) solvate has promising applications in novel magnetics with supramolecular structures.     

Cover Feature: Coordination-Cage-Catalysed Hydrolysis of Organophosphates: Cavity- or Surface-Based? (Chem. Eur. J. 14/2020)

The hydrophobic central cavity of a water-soluble M₈L₁₂ cubic coordination cage can accommodate a range of phospho-diester and phospho-triester guests such as the insecticide “dichlorvos” (2,2-dichlorovinyl dimethyl phosphate) and the chemical warfare agent analogue di(isopropyl) chlorophosphate. The accumulation of hydroxide ions around the cationic cage surface due to ion-pairing in solution generates a high local pH around the cage, resulting in catalysed hydrolysis of the phospho-triester guests. A series of control experiments unexpectedly demonstrates that—in marked contrast to previous cases—it is not necessary for the phospho-triester substrates to be bound inside the cavity for catalysed hydrolysis to occur. This suggests that catalysis can occur on the exterior surface of the cage as well as the interior surface, with the exterior-binding catalysis pathway dominating here because of the small binding constants for these phospho-triester substrates in the cage cavity. These observations suggest that cationic but hydrophobic surfaces could act as quite general catalysts in water by bringing substrates into contact with the surface (via the hydrophobic effect) where there is also a high local concentration of anions (due to ion pairing/electrostatic effects).     

DFT Study of the BH4− Hydrolysis on Au(111) Surface

The mechanism of the catalytic hydrolysis of BH₄⁻ on Au(111) as studied by DFT is reported. The results are compared to the analogous process on Ag(111) that was recently reported. It is found that the borohydride species are adsorbed stronger on the Au⁰-NP surface than on the Ag⁰-NP surface. The electron affinity of the Au is larger than that of Ag. The results indicate that only two steps of hydrolysis are happening on the Au(111) surface and the reaction mechanism differs significantly from that on the Ag(111) surface. These remarkable results were experimentally verified. Upon hydrolysis, only three hydrogens of BH₄⁻ are transferred to the Au surface, not all four, and H₂ generation is enhanced in the presence of surface H atoms. Thus, it is proposed that the BH₄⁻ hydrolysis and reduction mechanisms catalyzed by M⁰-NPs depend considerably on the nature of the metal.     

Cover Feature: Copper and Nickel Complexes of Oxamate−Phenol Containing Ligands: A Structural Dichotomy in Oxidized Species (Eur. J. Inorg. Chem. 15/2023)

The copper and nickel complexes of two tetradentate ligands derived from bis(aminophenol) and bis(phenol) architectures connected by an oxamate linker were isolated. Depending on the metal and ligand, the complex is isolated with either an intact (deprotonated) ligand ( 1²⁻ ), one-electron oxidized ligand ( 2⁻ ) or quinone form ( 3 ). Surprisingly, the Mannich base is easier to oxidize than the amidophenol derivatives. The complexes were characterized by X-ray diffraction, cyclic voltammetry, UV-Vis-NIR and EPR spectroscopies. Complex 1 shows two reversible oxidation waves assigned to the successive iminosemiquinone/aminophenolate redox systems. Complex 2⁻ shows an intense NIR feature, as well as an EPR signal at g_iso=2.043, consistent with a metallic contribution to the main ligand radical SOMO. Complex 3 shows the typical feature of an isolated Cu(II) complex. Spectro-electrochemistry coupled to DFT calculations demonstrate a ligand-centered oxidative redox chemistry for all the complexes.     

Role of the V(V)/ 1O2Complex in Oxidative Reactions in the H2O2/V(V)/AcOH System: Oxidation of Alkenes and Anthracenes

Anthracene and its alkyl derivatives undergo oxidation in the V^(V)/H₂O₂/AcOH system via a nonradical mechanism through the intermediate formation of the vanadium(V) complex with singlet dioxygen as a ligand. The ¹O₂molecule is transferred from this complex to an unsaturated substrate. The free singlet dioxygen ¹O₂(¹ _g ) is almost inactive toward anthracene in AcOH solution. Consequently, the vanadium(V) complex with singlet dioxygen is the only oxidant species active in the reaction. The ratio between the rate constant of the reaction of this complex with 2-ethylanthracene and the rate constant of its deactivation is an order of magnitude greater than the ratio between the rate constant of the reaction of dissolved free singlet dioxygen with the same substrate and the rate constant of its deactivation (physical quenching).     

The Unprecedented [S4N2O10]2− Anion in the Molecular Gold Complexes [Au2Br2(S4N2O10)2] and [Au2Cl2(S4N2O10)2](S2O5Cl2)

The reaction of hexachlorophosphazene, P₃N₃Cl₆, with SO₃ and the gold halides AuCl₃ and AuBr₃, respectively, leads to the new cyclic anionic tetramer, [S₄N₂O₁₀]²⁻, which is coordinated to Au³⁺ in the dimeric complexes [Au₂X₂(S₄N₂O₁₀)₂] (X=Cl, Br). The [S₄N₂O₁₀]²⁻ anion can be seen as the condensation product of two sulfate anions, [SO₄]²⁻_, and two amidosulfate anions, [NH₂SO₃]⁻.