Tareq Irshaidat

Reaction of Some Schiff Base Complexes of Iron(III) with Nitrogen and Sulfur Donor Anions

Abstract Reactions of some Schiff bases with Fe(III) salts in the presence of nitrogen or sulfur donor anions have been investigated. The Schiff bases are derived from the reaction of salicylaldehyde, substituted salicyaldehyde or 2-hydroxy-1 -naphthaldehyde with 8-aminoquinoline, substituted aniline, ethylenediamine or o-phenylenediamine. The obtained Schiff bases act either as tridentate or tetradentate dibasic ligands. Tentative structures have been assigned on the basis of elemental analyses, conductivity, spectral and magnetic data. Most of the obtained complexes are proposed to be hexa-coordinate but some might be penta-coordinate. The added anions (thiocynate, 8-aminoquinolate, pyrrolidinedithiocarbamate or piperazinedi(dithiocarbamate) are bonded to iron, in addition to the Schiff base, producing mononuclear complexes or act as bridging groups producing dinuclear or polynuclear complexes.

On the Factors Affecting H-Bonding : A CCSD(T) // B3LYP Study on Malonaldehyde Cation-Radical

Among the factors that may affect H-bond strength, the effect of the molecular ionization has not received any considerable attention. Here, malonaldehyde and its cation-radical as models were studied using DFT (B3LYP) and ab-initio theories (HF, MP2, and CCSD(T)). Based on establishing a comparison with the CCSD(T)/CBS energy barrier (from literature), we have found that the CCSD(T)/D95(d,p)//B3LYP/6-31G(d,p) computational protocol can be used as a reference for evaluating performance of the B3LYP and the MP2 methods on this model. In this computational organic chemistry study several aspects were investigated, they are: structures, energies, natural population analysis (NPA) charges, intramolecular charge transfer (delocalization) energies, and atoms in molecule (AIM) electron densities with regard to the Hbonding. The results indicate that loss of an electron can cause considerable effects on the various electronic structure aspects and the details are presented and discussed. All the aspects confirm that ionizing the molecule disturbs the electron density distribution in the HOMO orbital and makes the two oxygen atoms, relatively, electron deficient centers which consequently weakens both the H1-O1 bond and the O2/H1-O1 H-bond. The details of this investigation are new addition to the hydrogen bond theory. Other types of molecular models and computational protocols are of interest for future investigations. Keyword: Malonaldehyde cation-radical; DFT; MP2; CCSD(T); NBO; AIM; H-bond.

Effect of the metal ion and the medium on the electronic structure of anthranilic acid: a modelling study on the Li and the BeH derivatives

This computational organic chemistry study illustrates that the size of the metal ion is a critical point in determining the bonding mode of the anthranilate (2-aminobenzoate). The beryllium model structure is the first example in the chemical literature on the ability of this amino acid to bond as N–O chelate. The medium has variable effect on the energies and the dipole moments of the studied models, which was found originating essentially from the differences in the atomic charges of the metals. Analysis of the molecular charge distribution allowed stating a new theory on the effect of the medium on the two pairs of isomers.

On the factors affecting tautomerism: consequences of N-substituents (Me/NR2) in structures derived from salicylaldimines

This computational organic chemistry study was performed using the B3LYP and the Hartree–Fock methods. Other methods were compared using two model compounds, and these methods are: second-order Møller–Plesset, fourth-order Møller–Plesset, quadratic configuration interaction with single and double excitation and coupled cluster single and double excitations. The study included discussions of the following aspects: the molecular structures, the harmonic oscillator measure of aromaticity, the energy differences between the tautomers, selected infrared stretching frequencies, the atomic charges (Mulliken and natural population analysis), selected NMR chemical shifts, the molecular orbital diagrams and the R groups. The calculations revealed that the electronic structure of salicylaldimines is sensitive to this substitution and may change the physical organic aspects including tautomerism significantly. The results illustrate that the proton–electron delocalisation as a sub-molecular event might be a controllable process when a powerful H-bond exists. This is a new discovery in the area of tautomerism-based functional materials that will help in fine-tuning their properties.

A DFT Study on Selected Physical Organic Aspects of the Fischer Carbene Intermediates [(M(CO)4(C(OMe)Me)]

Fischer carbenes are important starting materials for C-C bond formation via coupling reactions between carbene and wide variety of substituted alkenes or alkynes. This DFT study shed light on unique fundamental organic/organometallic aspects for the C(OMe)Me carbene in the free form and in case of bonding with M(CO)4 (M= Cr, Mo, W). The data illustrate that the structures of the title intermediates include a unique structure stabilizing intramolecular M…C-H interaction (agostic interaction). This conclusion was made based on calculated NMR data (for carbon and hydrogen), structural parameters, energy calculations of conformers (C-C conformation), selected IR stretching frequencies (C-O, C-C, and C-H), and atomic charges. The agostic interaction is most efficient in case of chromium and in general is described as an overlap between the σ-bond electron pair of C-H with an empty d-orbital of the metal. These characterized examples are new addition to the orbital interaction theory.

Synthesis and Characterization of Some Unsymmetrical Schiff Bases and Their Copper ( II ) and Nickel ( II ) Complexes

The >C=N- unit is an important functional group in organic and bioorganic chemistry. In this study, the possibility of synthesizing unsymmetrical azo-methine Schiff bases was investigated. Successful isolation of tetra-dentate Schiff bases has been accomplished using phenylenediamine derivatives in conjunction with 1-hydroxy-2-acetonaphthone, and salicylaldehyde or 2-hydroxynaphthaldehyde. Nickel(II) and copper(II) salts were found to react with these compounds to produce neutral complexes of the general formula [ML]. On the other hand, it was necessary to employ the template method to complete the reaction between the monocondensate (derived from 1-hydroxy-2-acetonaphthone and phenylenediamine derivative) with 2-pyridinecarbaldehyde (PyL), 2-pyrrolecarbaldehyde (PL), and 2-quinolinecarbaldehyde (QL). The isolated compounds were characterized by means of NMR, IR, elemental analysis, MS, UVVis, magnetic susceptibility, and melting point measurement techniques. Theoretical calculations using the DFT/B3LYP theory illustrate that despite the extended conjugation, the isolated complexes are not planar, which is attributed to two main sources of steric hindrance. In addition to their importance as pigments, preliminary biological activity evaluation indicates that some of the complexes may be examined further as potential anti-tumor agents.

MODULATING THE ELECTRONIC STRUCTURE OF AMINO ACIDS: INTERACTION OF MODEL LEWIS ACIDS WITH ANTHRANILIC ACID

On the basis of theoretical B3LYP calculations, Yanez and co-workers (J. Chem. Theory Comput. 2012, 8, 2293) illustrated that beryllium ions are capable of significantly modulating (changing) the electronic structures of imidazole. In this computational organic chemistry study, the interaction of this β-amino acid and five model Lewis acids (BeF1+, Be2+, AlF21+, AlF2+, and Al3+) were investigated. Several aspects were addressed: natural bond orbitals, including second order perturbation analysis of intra-molecular charge delocalization and the natural population analysis atomic charges; molecular geometries; selected infrared stretching frequencies (C-N, C-O, and N-H), and selected 1H-NMR chemical shifts. The data illustrate that this interaction can weaken the H-O bond and goes beyond strengthening the intra-molecular hydrogen bond (N...H-O) to cause a spontaneous transfer of the proton to the nitrogen atom in five cases generating zwitterion structures. Many new features are observed. Most importantly, the zwitterion structures include a stabilizing hydrogen bond (N-H...O) that varies in relative strength according to the Lewis acid. These findings explain the experimental observations of α-amino acids (for example: J. Am. Chem. Soc. 2001, 123, 3577) and are the first reported fundamental electronic structure characterization of β-amino acids in zwitterion form.

The Effect of Substituents on Characteristics of Functional Material: Consequences of Fusing Schiff Bases and Some of Its Proton Substitutes on Isobenzofuran

Research on functional materials is one of the hot technology-related topics. Isobenzofurans and Schiff bases are important building blocks for functional materials. In this study, fundamental aspects of hybrid structures were studied based on B3LYP calculations. The results confirm that fused ortho-amino Schiff bases can have significant impact on the electronic structure of isobenzofuran. The derivatives are unique structures, the magnetic (NICS(0)) / geometric (HOMA) data illustrate that they exhibit the highest π -system localization known for aromatic compounds. The data also provide evidence that the elements in groups 1A, 2A, and 3A can induce a ring current, which is described by “percent aromatic character” with respect to the reference structure. The moderate induction of aromaticity in the fused chelates is associated with significant localization of the atomic charges (APT scheme). However, this computational organic chemistry study identifies for the first time in the chemical literature structures that can be described as aromatic metalla-hetero[14]annulenes (metal-based polycyclic aromatic structures). The band gap calculations of the frontier orbitals revealed that these derivatives are better conductors and chromophores at the molecular level than isobenzofuran. This approach suggests that similar chelates may be used to fine-tune the physical properties of building blocks of functional materials. From a fundamental organic chemistry point of view, the molecular changes are unique and novel as it appears from the chemical literature.