Narrow Results

Ab initio calculations were performed to study the applicability and reliability of the semi quantitative model based on the local hard-soft acid-base principle in studying the interaction of metal ions with ligands. The particular attention is devoted to the interaction of CO, CN^- and SCN^- as the base with some hard metal ions (Li⁺, Na⁺, K⁺) and some soft metal ions (Pd⁺², Ag⁺², Cd⁺²) as acids. The interaction energies were calculated using the HSAB principle and compared with the values obtained by the conventional MP2 method. The results show that the HSAB principle does not work in many cases and it fails to predict correct values for interaction energies. The AIM and NBO analyses were also performed to characterize the nature of the metal ion-ligand interaction. It is found that the charge transfers have great significance in the interaction of metal ions with ligands.

A theoretical investigation about the cooperative effect on (HCN)_n homo and (HCN)_n ⋯ HF heterochains was performed in terms of structural parameters and topological properties obtained in concordance with the protocol of Bader's atoms in molecules theory. Initially, the hydrogen bonding distances, electronic densities, and Laplacian descriptors were used to characterize small (HCN)_n and (HCN)_n ⋯ HF chains formed by n = 2–4 units of HCN. Hydrogen bond distances and distribution of charge density have revealed that the cooperative effect on (HCN)_n ⋯ HF heterochains is ruled by the polarity of the extreme hydrofluoric acid species. Furthermore, we investigated larger homo and heterochain systems formed by n = 2–8 molecules of HCN. In this insight, the drastic polarized effect caused by HF molecule which was considered very substantial at prior, in fact is seriously limited by an excessive number of HCN molecules connected to the heterochain. This leads to a stabilization of the (N ⋯ HF) hydrogen bonds with invariable electronic density in the range of . In this stage and henceforth, the cooperative effect is re-established with n = 4 molecules of HCN. Thereby, the electronic density of the hydrogen bonds become unaltered within the (HCN)_n ⋯ HF heterochains.

B3LYP/6-311++G** calculations have been carried out to simulate the influence of substitutions in position R₁ and R₂ of 3-amino 2-iminomethyl acryl aldehyde on intramolecular hydrogen bond strength. The following substituents are taken into considerations: CN, NO₂, Cl, F, CH₃, CHO, NH₂, C₂H₅, SH, SCH₃, CF₃ and CH₃CO and their vibrational frequencies are calculated at the same level of theory. Quantum theory of "Atoms in Molecules" and Natural Bond Orbitals method were applied to analyzed H-bond interactions. The electron density (ρ) and Laplacian (∇²ρ) properties, estimated by AIM calculations, indicate that N⋯H bond possesses low ρ and positive ∇²ρ values which are in agreement with electrostatic character of the HBs, whereas N–H bonds have covalent character (∇²ρ < 0). Natural population analysis data, the electron density and Laplacian properties, as well as, ν_(N-H) and γ_(N-H) have been used to evaluate the hydrogen bonding interactions.

The reaction mechanism of SiHF radical with HNCO has been investigated by the B3LYP method of density functional theory (DFT), while the geometries and harmonic vibration frequencies of reactants, intermediates, transition states and products have been calculated at the B3LYP/6-311++G** level. To obtain more precise energy result, stationary point energies were calculated at the CCSD(T)/6-311++G**//B3LYP/6-311++G** level. In temperature range of 100 K to 1900 K, the statistical thermodynamics and Eyring transition state theory with Winger correction are used to study the thermodynamic and kinetic characters of the channel with low energy barrier at 1.0 Atm. SiHF + HNCO → IM8 → TS8 → SiFNHCHO(P3) was the main channel with low potential energy in the singlet state, SiFNHCHO was the main product. The analyses for the combining interaction between SiHF radical and HNCO with the atom-in-molecules (AIM) theory have been performed. There are three reaction channels in the triplet.

The pnicogen bonding interactions of PCl₃ and π-electron systems (acetylene, ethylene, benzene) were calculated by using MP2/aug-cc-pVDZ method and the effect of hydrogen bond on pnicogen bond systems were investigated. It has been indicated that the hydrogen bonding and the pnicogen bonding interactions have influence on each other and the positively cooperative effect has been detected. The interaction energies of pnicogen bonded supramolecular system were also calculated by using DFT method (M06-2X) and some simple comparisons with those by using MP2 method were made. It has been disclosed from natural bond orbitals (NBO) analysis that more the amount of charge transfer of pnicogen bonding interaction, the greater the stability of the corresponding complex. Through AIM topological analysis, it has been revealed that the electron density of pnicogen bond BCP point is positively correlated with the stability of trimeric complex. Electron localization function (ELF) was also adopted to analyze the nature of pnicogen bonding interactions. Furthermore, density difference function (DDF) method was adopted to analyze the variation of electron density of pnicogen bond system because of hydrogen bond.

The computational investigations on 1:1 complexes of the nitrogen trifluoride (NF${}_3)$ species with the nitroxyl (HNO) species have been carried out, which reveal the existence of the nine complexes on the singlet potential energy surface (PES). The atoms in molecules (AIM) theory and the electron localization function (ELF) along with the identification of noncovalent interaction (NCI) regions and the investigation of electron transfer of all the obtained complexes have been carried out to provide suitable insight into the electronic and structural properties of these complexes. The calculated results reveal that the N-atom of the NF₃ species and the O-atom of the HNO species have more key roles compared with the F-atom of the NF₃ species and the N-atom of the HNO species in the obtained complexes.