A multi-descriptor analysis of substituent effects on the structure and aromaticity of benzene derivatives: π-Conjugation versus charge effects.

This work provides a detailed multi-component analysis of aromaticity in monosubstituted (X = CH, C , C , NH, NH, NH, OH, O, and O) and para-homodisubstituted (X = CH, CH, NH, NH, OH, and O) benzene derivatives. We investigate the effects of substituents using single-reference (B3LYP/DFT) and multireference (CASSCF/MRCI) methods, focusing on structural (HOMA), vibrational (AI(vib)), topological (ELF), electronic (MCI), magnetic (NICS), and stability (S-T splitting) properties. The findings reveal that appropriate π-electron-donating and π-electron-accepting substituents with suitable size and symmetry can interact with the π-system of the ring, significantly influencing π-electron delocalization.

High-Level Multireference Investigations on the Electronic States in Single-Vacancy (SV) Graphene Defects Using a Pyrene-SV Model.

The nonplanar character of graphene with a single carbon vacancy (SV) defect is investigated utilizing a pyrene-SV model system by way of complete-active-space self-consistent field theory (CASSCF) and multireference configuration interaction singles and doubles (MR-CISD) calculations. Planar structures were optimized with both methods, showing the B state to be the ground state with three energetically close states within an energy range of 1 eV. These planar structures constitute saddle points.

Red-emitting heteroleptic iridium(III) complexes: photophysical and cell labeling study.

Two red-emitting heteroleptic iridium(III) complexes (Ir-p and Ir-q) were synthesized and their photophysical and biological properties were analyzed. After their structures have been confirmed by several techniques, such as H NMR, C NMR, FT-IR, UV-Vis, and MALDI TOF analyses, their luminescence behavior was investigated in ethanol and PBS (physiological medium, pH ~ 7.4) solutions.

Relating Bond Strength and Nature to the Thermodynamic Stability of Hypervalent Togni-Type Iodine Compounds.

The bond strength and nature of a set of 32 Togni-like reagents have been investigated at the M062X/def2-TZVP(D) level of theory in acetonitrile described with the SMD continuum solvent model, to rationalize the main factors responsible for their thermodynamic stability in different conformations, and trifluoromethylation capabilities. For the assessment of bond strength, we utilized local stretching force constants and associated bond strength orders, complemented with local features of the electron density to access the nature of the bonds. Bond dissociation energies varied from 31.

Metal-Halogen Bonding Seen through the Eyes of Vibrational Spectroscopy.

Incorporation of a metal center into halogen-bonded materials can efficiently fine-tune the strength of the halogen bonds and introduce new electronic functionalities. The metal atom can adopt two possible roles: serving as halogen acceptor or polarizing the halogen donor and acceptor groups. We investigated both scenarios for 23 metal-halogen dimers trans-M(Y)(NCHX-3) with M = Pd(II), Pt(II); Y = F, Cl, Br; X = Cl, Br, I; and NCHX-3 = 3-halopyridine.

Pushing 3c-4e Bonds to the Limit: A Coupled Cluster Study of Stepwise Fluorination of First-Row Atoms.

To better understand why hypervalent F, O, N, C, and B compounds are rarely stable, we carried out a systematic study of 28 systems, including anionic, cationic, and neutral molecules, held together by covalent, hypervalent, and noncovalent bonds. Molecular geometries, frequencies, atomic charges, electrostatic potentials, energy and electron densities, Mayer bond orders, local stretching force constants, and bond strength orders (BSOs) were derived from high accuracy CCSD(T) calculations and utilized to compare the strength and nature of hypervalent bonds with other types of bonds. All hypervalent molecules studied in this work were found to be either first-order transition states or unstable to dissociation, with F and OF as the only exceptions.

Quantitative Assessment of Tetrel Bonding Utilizing Vibrational Spectroscopy.

A set of 35 representative neutral and charged tetrel complexes was investigated with the objective of finding the factors that influence the strength of tetrel bonding involving single bonded C, Si, and Ge donors and double bonded C or Si donors. For the first time, we introduced an intrinsic bond strength measure for tetrel bonding, derived from calculated vibrational spectroscopy data obtained at the CCSD(T)/aug-cc-pVTZ level of theory and used this measure to rationalize and order the tetrel bonds. Our study revealed that the strength of tetrel bonds is affected by several factors, such as the magnitude of the -hole in the tetrel atom, the negative electrostatic potential at the lone pair of the tetrel-acceptor, the positive charge at the peripheral hydrogen of the tetrel-donor, the exchange-repulsion between the lone pair orbitals of the peripheral atoms of the tetrel-donor and the heteroatom of the tetrel-acceptor, and the stabilization brought about by electron delocalization.

Systematic Coupled Cluster Study of Noncovalent Interactions Involving Halogens, Chalcogens, and Pnicogens.

The noncovalent interactions of 32 complexes involving pnicogens, chalcogens, and halogens atoms were investigated at the CCSD(T)/aug-cc-pVTZ level of theory. Two different types of complexes could be distinguished on the basis of geometric parameters, electron difference densities, and the charge transfer mechanisms associated with each type. In the type I conformation, the monomers adopt a skewed orientation allowing charge to be transfer between both monomers, whereas in the type II conformation the monomers adopt a linear arrangement, maximizing charge transfer in only one direction.

The Many Facets of Chalcogen Bonding: Described by Vibrational Spectroscopy.

A diverse set of 100 chalcogen-bonded complexes comprising neutral, cationic, anionic, divalent, and double bonded chalcogens has been investigated using ωB97X-D/aug-cc-pVTZ to determine geometries, binding energies, electron and energy density distributions, difference density distributions, vibrational frequencies, local stretching force constants, and associated bond strength orders. The accuracy of ωB97X-D was accessed by CCSD(T)/aug-cc-pVTZ calculations of a subset of 12 complexes and by the CCSD(T)/aug-cc-pVTZ //ωB97X-D binding energies of 95 complexes. Most of the weak chalcogen bonds can be rationalized on the basis of electrostatic contributions, but as the bond becomes stronger, covalent contributions can assume a primary role in the strength and geometry of the complexes.

The Peculiar Role of the Au Unit in Au Clusters: σ-Aromaticity of the AuZn Ion.

The stability of small Au (m = 4-7) clusters is investigated by analyzing their energetic, geometric, vibrational, magnetic, and electron density properties. Gold clusters can be constructed from stable cyclic 3-center-2-electron (3c-2e) Au units (3-rings) with σ-aromaticity. The stabilization requires a flow of negative charge from internal 3-rings with electron-deficient bonding to peripheral 3-ring units with stronger Au-Au bonds.

Quantitative Assessment of Halogen Bonding Utilizing Vibrational Spectroscopy.

A total of 202 halogen-bonded complexes have been studied using a dual-level approach: ωB97XD/aug-cc-pVTZ was used to determine geometries, natural bond order charges, charge transfer, dipole moments, electron and energy density distributions, vibrational frequencies, local stretching force constants, and relative bond strength orders n. The accuracy of these calculations was checked for a subset of complexes at the CCSD(T)/aug-cc-pVTZ level of theory. Apart from this, all binding energies were verified at the CCSD(T) level.

The intrinsic strength of the halogen bond: electrostatic and covalent contributions described by coupled cluster theory.

36 halogen-bonded complexes YXAR (X: F, Cl, Br; Y: donor group; AR acceptor group) have been investigated at the CCSD(T)/aug-cc-pVTZ level of theory. Binding energies, geometries, NBO charges, charge transfer, dipole moments, electrostatic potential, electron and energy density distributions, difference density distributions, vibrational frequencies, local stretching and bending force constants, and relative bond strength orders n have been calculated and used to order the halogen bonds according to their intrinsic strength. Halogen bonding is found to arise from electrostatic and strong covalent contributions.