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Herein, we describe the Ru-catalyzed C-H alkenylation of 1,4-naphthoquinones (1,4-NQs), resulting in 1,4-naphthoquinoidal/SuFEx hybrids with moderate to good yields. This method provides a novel route for direct access to ethenesulfonyl-fluorinated quinone structures. We conducted mechanistic studies to gain an in-depth understanding of the elementary steps of the reaction. Additionally, we evaluated the prototypes against trypomastigote forms of T. cruzi, leading to the identification of compounds with potent trypanocidal activity.

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Herein, we predict the first set of covalently bonded triatomic molecular compounds composed exclusively of noble gases. Using a combination of double-hybrid DFT, CCSD(T), and MRCI+Q calculations and a range of bonding analyses, we explored a set of 270 doubly charged triatomics, which included various combinations of noble gases and main group elements. This extensive exploration uncovered nine noble-gas-exclusive covalent compounds incorporating helium, neon, argon, or combinations thereof, exemplified by cases such as He32+ and related systems. This work brings to light a previously uncharted domain of noble gas chemistry, demonstrating the potential of noble gases in forming covalent molecular clusters.

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Invited for the cover of this issue are the groups of Holger Braunschweig at the Julius-Maximilians-Universität Würzburg, Germany and Eufrânio N. da Silva Júnior at the Universidade Federal de Minas Gerais, UFMG, Brazil. The image depicts the electrochemical synthesis of selenium-containing BODIPY molecules with lightning symbolizing the electrifying synthetic process, while the surrounding elemental chaos hints at the red-shifted absorption and emission and the transformative photophysical properties of these new compounds. Read the full text of the article at 10.1002/chem.202303883.

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We report a rapid, efficient, and scope-extensive approach for the late-stage electrochemical diselenation of BODIPYs. Photophysical analyses reveal red-shifted absorption - corroborated by TD-DFT and DLPNO-STEOM-CCSD computations - and color-tunable emission with large Stokes shifts in the selenium-containing derivatives compared to their precursors. In addition, due to the presence of the heavy Se atoms, competitive ISC generates triplet states which sensitize 1 O2 and display phosphorescence in PMMA films at RT and in a frozen glass matrix at 77 K. Importantly, the selenium-containing BODIPYs demonstrate the ability to selectively stain lipid droplets, exhibiting distinct fluorescence in both green and red channels. This work highlights the potential of electrochemistry as an efficient method for synthesizing unique emission-tunable fluorophores with broad-ranging applications in bioimaging and related fields.

Assuntos

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The discovery of C60, C60+, and C70 in the interstellar medium has ignited a profound interest in the astrochemistry of fullerene and related systems. In particular, the presence of diffuse interstellar bands and their association with C60+ has led to the hypothesis that hydrogenated derivatives, known as fulleranes, may also exist in the interstellar medium and contribute to these bands. In this study, we systematically investigated the structural and spectroscopic properties of C60Hn+q (n = 0-4, q = 0,1) using an automated global minimum search and density functional theory calculations. Our results revealed novel global minimum structures for C60H2 and C60H4, distinct from previous reports. Notably, all hydrogenated fullerenes exhibited lower ionization potentials and higher proton affinities compared to C60. From an astrochemical perspective, our results exposed the challenges in establishing definitive spectroscopic criteria for detecting fulleranes using mid-infrared and UV-Vis spectroscopies. However, we successfully identified distinct electronic transitions in the near-infrared range that serve as distinctive signatures of cationic fulleranes. We strongly advocate for further high-resolution experimental studies to fully explore the potential of these transitions for the interstellar detection of fulleranes.

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We report the unique heterobimetallic dodecanuclear oxamate-based {CoII6CuII6} nanowheel obtained using an environmentally friendly synthetic protocol. The effective Hamiltonian methodology employed herein allows the rationalisation of magnetic isotropic or anisotropic metal clusters, being a significant advance for future studies of exciting properties only observed at low and ultralow temperatures.

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The development of complexes featuring low-valent, multiply bonded metal centers is an exciting field with several potential applications. In this work, we describe the design principles and extensive computational investigation of new organometallic platforms featuring the elusive manganese-manganese bond stabilized by experimentally realized N-heterocyclic carbenes (NHCs). By using DFT computations benchmarked against multireference calculations, as well as MO- and VB-based bonding analyses, we could disentangle the various electronic and structural effects contributing to the thermodynamic and kinetic stability, as well as the experimental feasibility, of the systems. In particular, we explored the nature of the metal-carbene interaction and the role of the ancillary η6 coordination to the generation of Mn2 systems featuring ultrashort metal-metal bonds, closed-shell singlet multiplicities, and positive adiabatic singlet-triplet gaps. Our analysis identifies two distinct classes of viable synthetic targets, whose electrostructural properties are thoroughly investigated.

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Rhodium(III) catalysis enabled C-H/N-H alkyne annulation of nonsymmetric imidazole derivatives. This study encompasses the synthesis of imidazoles from a naturally occurring quinoidal compound and their use for the preparation of rigid π-extended imidazole derivatives with outstanding fluorescence. Our study also brings to light the photophysical aspects and the mechanism of the reaction studied via computational calculations. This method provided an efficient and versatile tool for the synthesis of fluorescent compounds with a wide range of chemical and biological applications.

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Splitting of molecular hydrogen (H2) into bridging and terminal hydrides is a common step in transition metal chemistry. Herein, we propose a novel organometallic platform for cleavage of multiple H2 molecules, which combines metal centers capable of stabilizing multiple oxidation states, and ligands bearing positioned pendant basic groups. Using quantum chemical modeling, we show that low-valent, early transition metal diniobium(ii) complexes with diphosphine ligands featuring pendant amines can favorably uptake up to 8 hydrogen atoms, and that the energetics are favored by the formation of intramolecular dihydrogen bonds. This result suggests new possible strategies for the development of hydrogen scavenger molecules that are able to perform reversible splitting of multiple H2 molecules.

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In this work, we report a systematic search of metastable C6Hn2+ (n = 1-6) dications from electron impact time-of-flight measurements of several benzene derivatives in combination with global minimum search based on the genetic algorithm. Our theoretical calculations reveal that the C6Hn2+ (n < 6) global minimum structures are completely different from that of the benzene dication, featuring linear carbon chains and/or cyclopropenylium moieties. Experimentally, the doubly charged species were investigated for a wide range of electron impact energies, from 20 to 2000 eV, for benzene and several monosubstituted compounds containing either electron-withdrawing or -donating groups. Furthermore, the C6Hn2+ production, evaluated from the yields of the dications with respect to that of the parent ion (or parent dication), was compared to those obtained from charge exchange in the doubly charged 2E spectra and electron impact experiments available in the literature. The yields of the long-lived benzene dications were contrasted to those analogues formed in chlorobenzene. Moreover, the formation of C6Hn2+ species is strongly dependent on the nature of substituent groups, with electron-withdrawing ones favoring the dication formation.

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Ionization and fragmentation pathways induced by ionizing agents are key to understanding the formation of complex molecules in astrophysical environments. Acetonitrile (CH3CN), the simplest organic nitrile, is an important molecule present in the interstellar medium. In this work, DFT and MP2 calculations were performed in order to obtain the low energy structures of the most relevant cations formed from electron-stimulated ion desorption of CH3CN ices. Selected reaction pathways and spectroscopic properties were also calculated. Our results indicate that the most stable acetonitrile cation structure is CH2CNH+ and that hydrogenation can occur successively without isomerization steps until its complete saturation. Moreover, the stability of distinct cluster families formed from the interaction of acetonitrile with small fragments, such as CHn+, C2Hn+, and CHnCNH+, is discussed in terms of their respective binding energies. Some of these molecular clusters are stabilized by hydrogen bonds, leading to species whose infrared features are characterized by a strong redshift of the N-H stretching mode. Finally, the rotational spectra of CH3CN and protonated acetonitrile, CH3CNH+, were simulated using distinct computational protocols based on DFT, MP2, and CCSD(T) considering centrifugal distortion, vibrational-rotational coupling, and vibrational anharmonicity corrections. By adopting an empirical scaling procedure for calculating spectroscopic parameters, we were able to estimate the rotational frequencies of CH3CNH+ with an expected average error below 1 MHz for J values up to 10.

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Born-Oppenheimer molecular dynamics (BOMD) and periodic density functional theory (DFT) calculations have been applied for describing the mechanism of formation of lithium fluoride (LiF) nanotubes with cubic, hexagonal, octagonal, decagonal, dodecagonal, and tetradecagonal cross-sections. It has been shown that high energy structures, such as nanowires, nanorings, nanosheets, and nanopolyhedra are transient species for the formation of stable nanotubes. Unprecedented (LiF)n clusters (n≤12) were also identified, some of them lying less than 10 kcal mol-[1] above their respective global minima. Such findings indicate that stochastic synthetic techniques, such as laser ablation and chemical vapor deposition, should be combined with a template-driven procedure in order to generate the nanotubes with adequate efficiency. Apart from the stepwise growth of LiF units, the formation of nanotubes was also studied by rolling up a planar square sheet monolayer, which could be hypothetically produced from the exfoliation of the FCC crystal structure. It was shown that both pathways could lead to the formation of alkali halide nanotubes, a still unprecedented set of one-dimensional materials.

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In free-radical halogenation of aromatics, singly charged ions are usually formed as intermediates. These stable species can be easily observed by time-of-flight mass spectrometry (TOF-MS). Here we used electron and proton beams to ionize chlorobenzene (C6H5Cl) and investigate the ions stability by TOF-MS. Additionally to the singly charged parent ion and its fragments, we find a significant yield of doubly and triply charged parent ions not previously reported. In order to characterize these species, we used high-level theoretical methods based on density functional theory (DFT), coupled-cluster (CC), and generalized valence bond (GVB) to calculate the structure, relative stabilities, and bonding of these dications and trications. The most stable isomers exhibit unusual carbon-chlorine multiple bonding: a terminal C═Cl double bond in a formyl-like CHCl moiety (1, rC-Cl = 1.621 Å) and a ketene-like C═C═Cl cumulated species (2, rC-Cl = 1.542 Å). The calculations suggest that an excited state of 2 has a nitrile-like C≡Cl triple bond structure.

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Different families of nanomaterials produced from the stabilization of diboryne (B≡B) units by multitopic N-heterocyclic carbenes (NHCs), such as nanowires, nanorings, and nanotents, were studied by computational methods. Density functional theory calculations with and without periodic boundary conditions were applied to estimate the dependence of the electronic and thermochemical properties of different diboryne macromolecules with respect to the nature of the bridging ligand. Our results show that all diboryne nanostructures studied herein are viable candidates for synthesis. The Janus-type multitopic naphthobis(imidazolylidene) (5), anthrobis(imidazolylidene) (10), and pyracenetetrakis(imidazolylidene) (16) compounds are the best candidates for generating diboryne nanowires. A path to covalent organic frameworks, nanocages, and nanotubes from the optimized diboryne nanostructures is also described. Rather than just scientific curiosity, diboryne nanostructures emerge as interesting targets for the synthesis of main-group nanomaterials.

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The generalized product function energy partitioning (GPF-EP) method is applied to the description of the cyclobutadiene molecule. The GPF wave function was built to reproduce generalized valence bond (GVB) and spin-coupled (SC) wave functions. The influence of quasiclassical and quantum interference contributions to each chemical bond of the system are analyzed along the automerization reaction coordinate for the lowest singlet and triplet states. The results show that the interference effect on the π space reduces the electronic energy of the singlet cyclobutadiene relative to the second-order Jahn-Teller distortion, which takes the molecule from a D4h to a D2h structure. Our results also suggest that the π space of the (1) B1g state of the square cyclobutadiene is composed of a weak four center-four electron bond, whereas the (3) A2g state has a four center-two electron π bond. Finally, we also show that, although strain effects are nonnegligible, the thermodynamics of the main decomposition pathway of cyclobutadiene in the gas phase is dominated by the π space interference.

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The generalized product function energy partitioning (GPF-EP) method has been applied to investigate the nature of the chemical bond and the origin of the inverted dipole moment of the BF molecule. The calculations were carried out with GPF wave functions treating all of the core electrons as a single Hartree-Fock group and the valence electrons at the generalized valence bond perfect-pairing (GVB-PP) or full GVB levels, with the cc-pVTZ basis set. The results show that the chemical structure of both X (1)Σ(+) and a (3)Π states is composed of a single bond. The lower dissociation energy of the excited state is attributed to a stabilizing intraatomic singlet coupling involving the B 2sp-like lobe orbitals after bond dissociation. An increase of electron density on the B atom caused by the reorientation of the boron 2sp-like lobe orbitals is identified as the main responsible effect for the electric dipole inversion in the ground state of BF. Finally, it is shown that π back-bonding from fluorine to boron plays a minor role in the electron density displacement to the bonding region in both states. Moreover, this effect is associated with changes in the quasi-classical component of the electron density only and does not contribute to covalency in either of the states. Therefore, at least for the case of the BF molecule, the term back-bonding is misleading, since it does not contribute to the bond formation.

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The benzene molecule is one of the most emblematic systems in chemistry, with its structural features being present in numerous different compounds. We have carried out an analysis of the influence of quantum mechanical interference on the geometric features of the benzene molecule, showing that many of the characteristics of its equilibrium geometry are a consequence of non-covalent contributions to the energy. This result implies that quasi-classical reasoning should be sufficient to predict the defining aspects of the benzene structure such as its planarity and equivalence of its bond lengths.

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The Generalized Product Function Energy Partitioning (GPF-EP) method has been applied to a set of molecules, AH (A = Li, Be, B, C, N, O, F), CO and LiF with quite different dipole moments, in order to investigate the role played by the quantum interference effect in the formation of polar chemical bonds. The calculations were carried out with GPF wave functions treating all the core electrons as a single Hartree-Fock group and the bonding electrons at the Generalized Valence Bond Perfect-Pairing (GVB-PP) level, with the cc-pVTZ basis set. The results of the energy partitioning into interference and quasi-classical contributions along the respective Potential Energy Surfaces (PES) show that the main contribution to the depth of the potential wells comes from the interference term, which is an indication that all the molecules mentioned above form typical covalent bonds. In all cases, the stabilization promoted by the interference term comes from the kinetic contribution, in agreement with previous results. The analysis of the effect of quantum interference on the electron density reveals that while polarization effects (quasi-classical) tend to displace electronic density from the most polarizable atom toward the less polarizable one, interference (quantum effects) counteracts by displacing electronic density to the bond region, giving rise to the right electronic density and dipole moment.

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The nature of the chemical bond in conjugated hydrocarbons is analyzed through the generalized product function energy partitioning (GPF-EP) method, which allows the calculation of the quantum-mechanical interference and quasi-classical contributions to the energy. The method is applied to investigate the differences between the chemical bonding in conjugated and non-conjugated hydrocarbon isomers and to evaluate the contribution from the energy components to the stabilization of the molecules. It is shown that in all cases quantum-mechanical interference has the effect of concentrating π electron density between the two carbon atoms directly involved in the (C-C)π bonds. For the conjugated isomers, this effect is accompanied by a substantial reduction of electron density in the π space of the neighbouring (C-C)σ bond. On the other hand, quasi-classical effects are shown to be responsible for the extra stabilization of the conjugated isomers, in which a decrease of the π space kinetic reference energy seems to play an important role. Finally, it is shown that the polarization of p-like orbitals in compounds with alternating single and double bonds ultimately increases electron density in the π space of the neighbouring (C-C)σ bond. Therefore, quasi-classical effects, rather than covalent ones, seem to be responsible for several properties of conjugated molecules, such as thermodynamic stability, planarity and (C-C)σ bond shortening. The shortcomings of the delocalization concept are discussed.

Assuntos