Hexacoordinate Bonding and Aromaticity in Silicon Phthalocyanine

The Huckel’s rule, Baird’s rule, and electronic shell closure model are classical and well-established concepts in chemistry, which have long been employed in rationalizing the aromaticity/antiarom...

In this paper, a detailed study of the local aromaticity in a series of cyclopenta-fused linear polyacenes (acenaphthylene derivatives) was performed using several different criteria of aromaticity. Namely, the energy effect (ef), bond resonance energy (BRE), harmonic oscillator model of aromaticity (HOMA) index, multi centre delocalization indices (MCI), electron density at ring critical points ρ(r(C)), nucleus independent chemical shifts (NICS) and ring current maps were employed. All these methods agree that the extent of aromaticity of the five-membered ring in the acenaphthylene molecule is quite small. On the other hand, it was shown that the aromatic character of the five-membered rings depends on the size of the polyacenic part and on the position of the five-membered ring along the polyacenic part of the given acenaphthylene derivatives. According to energetic, electron delocalization and geometrical indices, the aromatic character of the pentagons in some higher acenaphthylene congeners is of the same order of magnitude as the aromatic character of some hexagons in the respective molecules. Ring current maps revealed the existence of a weak paratropic (antiaromatic) circulation in the five-membered rings which, in the case of higher members of the homolog series, becomes weaker. In contrast, the NICS indices showed a significant antiaromatic character of the five-membered rings in higher members of the acenaphthylene series.

The effect of benzo-annelation on the local aromaticity of the central ring of acridine (1), 9H-carbazole (2), dibenzofuran (3), and dibenzothiophene (4) was analyzed by means of the energy effects (ef), pairwise energy effects (pef), multicenter delocalization index (MCI), electron density at ring critical points (ρ(r(C))), harmonic oscillator model of aromaticity (HOMA), and nucleus independent chemical shifts (NICS). According to energetic, electron delocalization, and geometrical indices, angular benzo-annelation increases, whereas linear benzo-annelation decreases, the extent of the local aromaticity of the central ring containing heteroatoms. The local aromaticity of the central heterocyclic ring in the examined molecules can significantly vary by applying different modes of benzo-annelation. The NICS values do not always support the results obtained by the other aromaticity indices and, in some cases, lead to completely opposite conclusions.

In this study, we investigated the exceptional basicity of diazahelicenes through a comprehensive computational analysis using DFT calculations. Eighteen diazahelicene compounds were examined and compared with 1,8-bis(dimethylamino)naphthalene (DMAN), revealing that most exhibit stronger basicity than DMAN, qualifying them as proton sponges. The study employed the M06-2X functional with the def2tzvp basis set to analyze proton affinity, gas-phase basicity (GB), and structural changes upon protonation. We found that the basicity is significantly influenced by the interplanar angle, hydrogen bonding, conjugation, and aromaticity of the compounds. Most compounds demonstrated a decrease in interplanar angle upon protonation, with compounds containing nitrogen atoms in close proximity showing frustrated base behavior. Aromaticity analysis using HOMA (Harmonic Oscillator Model of Aromaticity) and Nucleus-independent Chemical Shift indices indicated enhanced electron delocalization after protonation. Further insights into electronic structure and bonding were obtained through AIM (atomic in molecules), MEP (molecule in electrostatic potential), NBO (Natural Bonding Orbital), ELF (electron localization function), and LOL (Localized Orbital Locator) analyses, providing a comprehensive understanding of the factors contributing to the exceptional basicity of these compounds.

Arylene Diimide Derivatives as Anolyte Materials with Two-Electron Storage for Ultrastable Neutral Aqueous Organic Redox Flow Batteries

The harmonic oscillator model of aromaticity (HOMA) has recently been reparametrized for assessing (anti)aromaticity of excited states. The derived HOMER has been tested on monocycles. In polycyclic compounds, the spin density (SD) per ring can span a wide range, and the question arises whether HOMER describes the (anti)aromaticity of all rings equally well. The purpose of this paper is to provide some information on this. The molecules studied are polybenzenoids and fused polycyclic systems composed of benzene ring(s) and one cyclobutadiene (CBD), cyclooctatetraene (COT) or pentalene unit. The results show that HOMA can be used for benzene subunits covering the entire SD range, while HOMER could be used with caution only for benzene rings adopting the main part of the SD. The aromaticity of CBD and the five-membered rings of the pentalene subunit is well described by HOMER and HOMA when their SD > 1, but the aromaticity of the COT subunits is better described by HOMA. For the perimeter of the pentalene subunit, HOMA can be used for the entire SD range, and HOMER when SD > 1.4. Interestingly, both HOMA and HOMER work very well for the 4n π-electron subunits and five-membered rings of the studied polycycles in their singlet state, while HOMA is preferable for the benzene subunits.

In the current study, the molecular structures of the two new azomethine dyes such as AAFOH-1 and AAFOH-2 have been investigated with the use of density functional theory (DFT/B3LYP/6-311+G(d)) in a DMSO solvent for the first time. The electronic spectra of the new dyes in a DMSO solvent were carried out by temporally dependent density functional theory (TD-DFT) method. The computed absorption spectral data of the investigated molecules are in good agreement with the experimental data, thus allowing an assignment of the UV/Vis spectra. The equilibrium geometry, the HOMO and LUMO molecular orbitals, excitation energies, oscillator strengths and natural bond orbital (NBO) analysis for the molecules have also been calculated and presented. The electron location function (ELF), localized orbital locator (LOL), and quantum theory of atoms in molecules (QTAIM) analyses were also carried out. On the basis of polyvinyl alcohol (PVA) and the new synthesized azomethine dyes polarizing films were developed. The main optical parameters of polarizing PVA-films (transmittance, polarization efficiency, and dichroic ratio) have been measured and discussed. Anizotropy of thermal conductivity of the PVA-films have been studied.

Harmonic oscillator model of aromaticity (HOMA) in conjugated radicals and cations

Quantum chemical simulations were utilized to investigate the nature of the bonding of N3-, P3-, As3-, O2-, S2-, Se2-, F-, Cl-, andBr- anions with the designed anion receptor cyclopenta-2,4-diene-1,1-diylbis(borane) abbreviated as CPDB and consecutive hyperconjugative aromaticity in its cyclopentadiene ring. Various analytical tools, including quantum theory of atoms in molecules (QTAIM), Electron Localization function (ELF), and reduced density gradient (RDG) were employed to explore the interaction between the selected anions and the CPDB structure. Moreover, the changes in the bond lengths (∆BL), harmonic oscillator model of aromaticity (HOMA), and localized orbital locator purely contributed by π-orbitals (LOL-π) analyses were performed to study the hyperconjugative aromaticity upon anion accepting. The findings indicate that the anions are connected to the CPDB structure through the electron deficiency of the B atoms and can induce the aromaticity via Schleyer's hyperconjugative aromaticity to the CPBD's ring. The nature of the interactions and hyperconjugative aromaticity effect of each anion is discussed in detail.

Cycloarenes are an essential class of polycyclic aromatic hydrocarbons with unique electronic structure, but their synthesis is very challenging. Herein, we report a facile synthetic strategy prima...

The molecular interaction between the chelating agents of citric acid (CA), ethylenediaminetetraacetic acid (EDTA), and triethylenetetraamine (TETA) with metals (M = Ba, Y, and Zr) were studied using Density Functional Theory (DFT) method. This study aims to determine the type of bonding between M–O/N bonds in the CA/EDTA/TETA– complexes. In this study, each metal was attached at strategic positions of chelating agents and was optimized at B3LYP/6-31G* and UGBS level of theory. The M–O bonds were characterized based on Atoms–in–molecules (AIM) and Electron Localization Function (ELF) in the topological analysis. In AIM analysis, the total electron energy density at the bond critical point (BCP) of the M–O/N bonds are used to estimate the interaction involved. The low values of ρ(r) and positive values of ∇2ρ(r) indicates that ionic character exists in the M–O/N bonds. In ELF color-filled map, the blue shaded region between M–O/N atom acts as an indicator for the existence of the ionic interaction. Both AIM and ELF results confirm the existence of ionic bonding between M–O/N bonds, with values of ρ(r) and ∇2ρ(r) ranging from 0.02 to 0.12 au and 0.09 to 0.5 au respectively. Further analysis on charge distribution at M–O/N bonds show that the opposite charge between Ba, Y, and Zr with O/N assured the M– O/N ionic bonding interactions. Keywords: Density functional theory, metals, bonding, atom–in–molecules, bond critical point, electron localization functions

We have witnessed considerable research interest in the recent literature about the development and applications of quantities from the information-theoretic approach (ITA) in density functional theory. These ITA quantities are explicit density functionals, whose local distributions in real space are continuous and well-behaved. In this work, we further develop ITA by systematically analyzing the topological behavior of its four representative quantities, Shannon entropy, two forms of Fisher information, and relative Shannon entropy (also called information gain or Kullback-Leibler divergence). Our results from their topological analyses for 103 molecular systems provide new insights into bonding interactions and physiochemical properties, such as electrophilicity, nucleophilicity, acidity, and aromaticity. We also compare our results with those from the electron density, electron localization function, localized orbital locator, and Laplacian functions. Our results offer a new methodological approach and practical tool for applications that are especially promising for elucidating chemical bonding and reactivity propensity.

The pharmaceutical proprieties of the 2,6-dimethylpiperazine-1,4-diium oxalate oxalic acid compound have been studied and the relevant drug design has been considered. The investigated organic compound with formula (2,6-(CH3)C4H10N2)2(C2O4)2·H2C2O4 (2DPOA) has been synthesized by slow evaporation technique at room temperature of a molar ratio 3:2 mix of oxalic acid and 2,6-dimethylpiperazine. Then 2DPOA has been characterized by IR, 13C NMR, UV–visible and the DFT calculation at the B3LYP level of theory has been made. The molecular structure and parameters (bond angles and lengths) of the molecule have been optimized using the Gaussian 09 software and compared with the XRD data. The atoms-in-molecules (AIM), electron localization function (ELF), and localized orbital locator (LOL) methods have been utilized to determine the types and nature of noncovalent interactions present within the 2DPOA molecule. These methods offer insights into the characteristics and behavior of these interactions. Furthermore, the presence of these interactions has been confirmed through the Hirshfeld Surface (HS) and reduced density gradient (RDG) analysis. The NBO analysis is employed to assess the charge exchange occurring within the studied compound. The molecular reactive sites have been examined using the molecular potential surface and Mulliken atomic charges. The energy gap between HOMO–LUMO and chemical properties of 2DPOA have been determined within the frontier molecular orbital theory. The UV–Vis spectrum of the 2DPOA molecule has been recorded and examined. The calculated and experimental infrared absorption and nuclear magnetic resonance spectra of 2DPOA molecule have been investigated. Finally, the molecular docking simulation has been used to find novel inhibitors and drugs for the cancer and epilepsy disease treatment.

Conceptual Density Functional Theory and Some Recent Developments

Imidazolium and its different N‐substituted derivatives are considered in this study to investigate their stability, reactivity, and acidity. Different aliphatic and aromatic ligands have been introduced in imidazolium to see their effect. It has been observed that the acidity of imidazolium systems increases with ligands having higher electron‐withdrawing nature. The studied systems are found to be weak acids, and weak bases can generate the corresponding carbene systems. The stability, reactivity, and aromaticity of all the systems are analyzed by using conceptual density functional theory (CDFT)‐based reactivity descriptors. Nucleus‐independent chemical shift (NICS) values lend additional support for the aromatic behavior of the studied molecules.