Project description:For the first time, the intermolecular orbital interaction between benzene and methane in the benzene-methane complex, a representative of weak interaction system, has been studied by us using ab initio calculations based on different methods and basis sets. Our results demonstrate obvious intermolecular orbital interaction between benzene and methane involving orbital overlaps including both occupied and unoccupied orbitals. Similar to interatomic orbital interaction, the intermolecular interaction of orbitals forms "bonding" and "antibonding" orbitals. In the interaction between occupied orbitals, the total energy of the complex increases because of the occupation of the antibonding orbital. The existence of the CH-π hydrogen bond between benzene and methane causes a decrease in rest energy level, leading to at least -1.51 kcal/mol intermolecular interaction energy. Our finding extends the concept of orbital interaction from the intramolecular to the intermolecular regime and gives a reliable explanation of the deep orbital reformation in the benzene-methane complex.
Project description:Stacking interactions have been evaluated, employing computational methods, in dimers formed by analogous aliphatic and aromatic species of increasing size. Changes in stability as the systems become larger are mostly controlled by the balance of increasing repulsion and dispersion contributions, while electrostatics plays a secondary but relevant role. The interaction energy increases as the size of the system grows, but it does much faster in π-π dimers than in σ-π complexes and more remarkably than in σ-σ dimers. The main factor behind the larger stability of aromatic dimers compared to complexes containing aliphatic molecules is related to changes in the properties of the aromatic systems due to electron delocalization leading to larger dispersion contributions. Besides, an extra stabilization in π-π complexes is due to the softening of the repulsive wall in aromatic species that allows the molecules to come closer.
Project description:Inspired by the double-aromatic (σ and π) C6H3 +, C6I6 2+, and C6(SePh)6 2+ ring-shaped compounds, herein we theoretically study their borazine derivative analogues. The systems studied are the cation and dications with formulas B3N3H3 +, B3N3Br6 2+, B3N3I6 2+, B3N3(SeH)6 2+, and B3N3(TeH)6 2+. Our DFT calculations indicate that the ring-shaped planar structures of B3N3H3 +, B3N3I6 2+, and B3N3(TeH)6 2+ are more stable in the singlet state, while those of B3N3Br6 2+ and B3N3(SeH)6 2+ prefer the triplet state. Besides, exploration of the potential energy surface shows that the ring-shaped structure is the putative global minimum only for B3N3I6 2+. According to chemical bonding analysis, B3N3H3 +, B3N3I6 2+, and B3N3(TeH)6 2+ have σ and π delocalized bonds. The number of delocalized σ/π electrons is 2/6 for the first, and 10/6 for the second and third, similar to what their carbon analogs exhibit. Finally, the analysis of the magnetically induced current density allows B3N3H3 +, B3N3I6 2+, and B3N3(TeH)6 2+ to be classified as strongly σ aromatic, and poorly π aromatic compounds.
Project description:MP2/aug-cc-pVTZ calculations were performed for complexes of BrF₃ and BrF₅ acting as Lewis acids through the bromine centre, with species playing a role of Lewis base: dihydrogen, acetylene, ethylene, and benzene. The molecular hydrogen donates electrons by its σ-bond, while in remaining moieties-in complexes of hydrocarbons; such an electron transfer follows from π-electrons. The complexes are linked by a kind of the halogen bond that is analyzed for the first time in this study, i.e., it is the link between the multivalent halogen and π or σ-electrons. The nature of such a halogen bond is discussed, as well as various dependencies and correlations are presented. Different approaches are applied here, the Quantum Theory of Atoms in Molecules, Natural Bond Orbital method, the decomposition of the energy of interaction, the analysis of electrostatic potentials, etc.
Project description:Perylene bisimide (PBI) dyes are known as red, maroon and black pigments, whose colors depend on the close π-π stacking arrangement. However, contrary to the luminescent monomers, deep-red and black PBI pigments are commonly non- or only weakly fluorescent due to (multiple) quenching pathways. Here, we introduce N-alkoxybenzyl substituted PBIs that contain close π stacking arrangement (exhibiting dπ-π ≈ 3.5 Å, and longitudinal and transversal displacements of 3.1 Å and 1.3 Å); however, they afford deep-red emitters with solid-state fluorescence quantum yields (ΦF) of up to 60%. Systematic photophysical and computational studies in solution and in the solid state reveal a sensitive interconversion of the PBI-centred locally excited state and a charge transfer state, which depends on the dihedral angle (θ) between the benzyl and alkoxy groups. This effectively controls the emission process, and enables high ΦF by circumventing the common quenching pathways commonly observed for perylene black analogues.
Project description:The weak noncovalent interactions and flexibility of ligands play a key role in enantioselective metal-catalyzed reactions. In transition metal complexes and their catalytic applications, the experimental assessment and the design of key interactions is as difficult as the prediction of the enantioselectivities, especially for flexible, privileged ligands such as chiral phosphoramidites. Therefore, the interligand interactions in cis-PdII L2 Cl2 phosphoramidite complexes were investigated by NMR spectroscopy and computations. We were able to induce a strong conformational preference by breaking the symmetry of the C2 -symmetric side chain of one of the ligands, and shift the equilibrium between hetero- and homocomplexes towards heterocomplexes because of interligand interactions in the cis-complexes. The modulation of aryl substituents was exploited, along with the solvent effect. The combined CH-π and π-π interactions reveal design patterns for binding and folding of chiral ligands and catalysts.
Project description:Naphthalenediimide derivates are a class of π-conjugated molecules largely investigated in the literature and used as building blocks for metal-organic frameworks or coformers for hydrogen-bond-based cocrystals. However, their tendency to establish halogen-bond interactions remains unexplored. By using a crystalline engineering approach, we report here four new cocrystals with N,N'-di(4-pyrydyl)-naphthalene-1,4,5,8-tetracarboxidiimide and diiodo-substituted coformers, easily obtained via a mechanochemical protocol. Cocrystals were characterized via NMR, electron ionization mass spectrometry, thermogravimetric analysis, powder X-ray diffraction, and single-crystal X-ray diffraction. Crystallographic structures were then finely examined and correlated with energy framework calculations to understand the relative contribution of halogen-bond and π-π interactions toward framework stabilization.
Project description:The mechanism of the reaction of lithium and magnesium carbenoids with ethylene to give cyclopropane has been explained in detail in all the steps at the G4 level of theory. We explored the lithium and magnesium interaction toward πC=C and σC-C bonds in the reactants and the products. We have also investigated the reaction path by means of the force profile formalism in order to highlight the electronic and the structural rearrangements along the potential energy surface of the cyclopropanation. The results indicate that all of the reactions are stepwise, exoenergetic, with low barriers. All our findings were confirmed by dynamic simulations for chlorometal carbenoids. Furthermore, from the intrinsic reaction coordinate procedure, we were able to find out the intermediates that can take place when the reaction is descending from the transition state to the products or reactants. The reaction force analysis at B3LYP/6-311G(d,p) indicates that the energy barriers are mostly due to structural rearrangements which are produced by the approach of the carbenoid to ethylene. Quantum theory of atoms in molecules and electron localization function analyses indicate that products, reactants, and intermediates form complexes stabilized by attractive forces between Li/Mg and single/double bonds.
Project description:We explore numerically and experimentally the formation of hybridized modes between a bright mode displayed by a gold nanodisc and either dark or bright modes of a nanorod - both elements being either separated by a nanometer-size gap (disconnected system) or relied on a metal junction (connected system). In terms of modeling, we compare the scattering or absorption spectra and field distributions obtained under oblique-incidence plane wave illumination with quasi-normal mode computation and an analytical model based on a coupled oscillator model. Both connected and disconnected systems have very different plasmon properties in longitudinal polarization. The disconnected system can be consistently understood in terms of the nature of hybridized modes and coupling strength using either QNMs or coupled oscillator model; however the connected configuration presents intriguing peculiarities based on the strong redistribution of charges implied by the presence of the metal connection. In practice, the fabrication of disconnected or connected configurations depends on the mitigation of lithographic proximity effects inherent to top-down lithography methods, which can lead to the formation of small metal junctions, while careful lithographic dosing allows one to fabricate disconnected systems with a gap as low as 20 nm. We obtained a very good agreement between experimentally measured scattering spectra and numerical predictions. The methods and analyses presented in this work can be applied to a wide range of systems, for potential applications in light-matter interactions, biosensing or strain monitoring.
Project description:As common coinage metals, silver and silver compounds have very rich application in the organic catalytic reaction. Immobilization of silver compounds on heterogeneous media is the most common way used in industrial catalytic reactions. In this work, we designed and synthesized a new heterogeneous porous silver catalyst, with in situ-formed Ag-S rods as connecting nodes and thiosemicarbazide-functionalized linear ligands, used in both σ- and π-catalytic transformations. Strong Ag-S bonds bypassed the loss of noble silver elements and inhibited the formation of nonporous silver particles which always led to the decrease of yields in homogenous reactions. Furthermore, various derivatives of propargylamines and phenylacetylenes were applied as both σ and π-active substrates with moderate to good yields.