Electronic Structure Principles Research Articles

Insights into the catalytic activity of boron-doped thiazoles in the Diels-Alder reaction.

The role of boron-doped thiazoles as a Lewis acid catalyst in [4+2] cycloaddition reaction between 1,3-butadiene and acrolein has been addressed. Three different organic heterocycles were designed to study their catalytic activity. It has been observed that these heterocycles efficiently work as catalysts than the well-known Lewis acid BF3. All the reactions follow the normal electron demand process and are exothermic. Different conceptual DFT-based reactivity descriptors and electronic structure principles such as maximum hardness and minimum electrophilicity lend additional support to the feasibility of the reaction mechanism. The reaction force (RF), reaction electronic flux (REF), and its different components exhibit a detailed electronic activity throughout the reaction.

Atoms-In-Molecules' Faces of Chemical Hardness by Conceptual Density Functional Theory.

The chemical hardness concept and its realization within the conceptual density functional theory is approached with innovative perspectives, such as the electronegativity and hardness equalization of atoms in molecules connected with the softness kernel, in order to examine the structure-reactivity equalization ansatz between the electronic sharing index and the charge transfer either in the additive or geometrical mean picture of bonding. On the other hand, the maximum hardness principle presents a relation with the chemical stability of the hardness concept. In light of the inverse relation between hardness and polarizability, the minimum polarizability principle has been proposed. Additionally, this review includes important applications of the chemical hardness concept to solid-state chemistry. The mentioned applications support the validity of the electronic structure principles regarding chemical hardness and polarizability in solid-state chemistry.

On the Periodicity of the Information Theory and Conceptual DFT-Based Reactivity Descriptors

The periodic trends in conceptual density functional and information theory-based reactivity descriptors are reported for the atoms H to Ba (Z = 1 to 56). Ionization potential, electron affinity, electronegativity, and hardness show periodic behavior following the Aufbau principle and popular electronic structure principles. They are in agreement with those reported in standard chemistry textbooks. The trend in the electrophilicity index, however, shows an interesting behavior, where it contradicts earlier reports. Our calculation reveals that the noble gas elements correspond to minimum ω values in each period which obey the minimum electrophilicity principle as well as reflect their low reactivity. Periodic trends in electroaccepting and electrodonating powers, along with that of net electrophilicity, are as expected. The behavior of information theory-based Shannon and GBP entropies, along with the Shannon entropy of shape function are also explored across the periodic table.

Giant exchange bias in antiferromagnetic Pr2CoFe0.5Mn0.5O6: a structural and magnetic properties study

Antiferromagnetic (AFM) materials with a colossal exchange bias (EB) effect find applications as high-density spintronic devices. We report structural (geometrical and electronic) and magnetic studies in the polycrystalline Pr2CoFe0.5Mn0.5O6 double perovskite system. The observed lack of training effect suggests the existence of robust EB. In addition, the detailed magnetic studies and Raman studies unravel the Griffith-like phase along with the spin-phonon coupling in the present system. The x-ray photoemission spectroscopy (XPS) analysis supports more than one valence state of B-site elements, which is accountable for the competition between ferromagnetic (FM) and AFM interactions in addition to the anti-site disorder in the system. The neutron measurement confirms the G-type AFM spin arrangement, accredited by the DFT calculation. The magnetic studies have correlated with the electronic structure, neutron study, and theoretical first principle calculations.

New mixed‐ligand iron(III) complexes containing thiocarbohydrazones: Preparation, characterization, and chemical reactivity analysis through theoretical calculations

Five new mixed ligand Fe(III) complexes, namely, [FeL1(acac)] (L1Fe), [FeL2(acac)] (L2Fe), [FeL3(acac)] (L3Fe), [FeL4(acac)] (L4Fe), and [FeL5(acac)] (L5Fe), were synthesized from the reaction of iron(III) acetylacetonate with [ONS] donor dibasic tridentate symmetrical bisthiocarbohydrazone ligands. Synthesized mixed ligand Fe(III) complexes were characterized with infrared spectra, UV‐Vis spectra, mass spectra, elemental analysis, magnetic susceptibility measurements, and thermogravimetric analysis. The molar conductance measurement in DMF solution confirmed that the complexes are nonelectrolytic. TGA analysis results showed that the thermal stability of the ligands and complexes was high. Antioxidant capacity and free radical scavenging activity of the mixed ligand Fe(III) complexes were investigated using CUPRAC and the DPPH radical scavenging method. Mixed ligand Fe(III) complexes showed higher antioxidant activity than ligands and reference compound. Popular conceptual density functional parameters like hardness, electrophilicity, dipole moment, and chemical potential for new ligands and their Fe(III) complexes were calculated and discussed. Chemical reactivity and stabilities of the studied chemical systems were analyzed with the help of well‐known electronic structure principles like maximum hardness principle (MHP), hard and soft acid–base (HSAB) principle, minimum polarizability principle, and minimum electrophilicity principle. L1Fe, which has the highest chemical hardness value, is the most stable complex according to MHP.

Electrophilicity index revisited.

This review aims to be a comprehensive, authoritative, critical, and accessible review of general interest to the chemistry community; because the electrophilicity index is a very useful global reactivity descriptor defined within a conceptual density functional theory framework. Our group has also introduced electrophilicity based new global and local reactivity descriptors and also new associated electronic structure principles, which are important indicators of structure, stability, bonding, reactivity, interactions, and dynamics in a wide variety of physico-chemical systems and processes. This index along with its local counterpart augmented by the associated electronic structure principles could properly explain molecular vibrations, internal rotations and various types of chemical reactions. The concept of the electrophilicity index has been extended to dynamical processes, excited states, confined environment, spin-dependent and temperature-dependent situations, biological activity, site selectivity, aromaticity, charge removal and acceptance, presence of external perturbation through solvents, external electric and magnetic fields, and so forth. Although electrophilicity and its local variant can adequately interpret the behavior of a wide variety of systems and different physico-chemical processes involving them, their predictive potential remains to be explored. An exhaustive review on all these aspects will set the tone of the future research in that direction.

Spectral, thermal and DFT studies of novel nickel(II) complexes of 2-benzoylpyridine-N4-methyl-3- thiosemicarbazone: Crystal structure of a square planar azido-nickel(II) complex

Novel six Ni(II) complexes of an NNS donor 2-benzoylpyridine-N4-methyl-3- thiosemicarbazone(HL) are synthesized and characterized. Various physicochemical techniques are applied for the study of the coordination behavior of the thiosemicarbazone to the nickel center. In all the complexes, thiosemicarbazone is coordinated in the thiolate form. A four coordinated Ni(II) complex [NiLN3] is crystallized and its molecular and crystal structures are determined by single-crystal X-ray crystallography. Single-crystal XRD reveals that the complex got crystallized in the monoclinic space group P21/n and nickel(II) has a square planar environment. Intramolecular hydrogen bonding interactions make the complex more rigid and in the crystal lattice, the intermolecular hydrogen bonding interactions generate a supramolecular 1 D chain. The chemical reactivity behavior of the HL and six Ni(II) complexes was evaluated with the CAM-B3LYP quantum chemical calculations. The validity of electronic structure principles like Maximum Hardness, Minimum Polarizability, and Minimum Electrophilicity Principle in the study is discussed.

Synthesis, spectroscopic characterization, DFT calculations, and molecular docking studies of new unsymmetric bishydrazone derivatives

Three new unsymmetric isatin bishydrazone compounds; Comp. I, II, III, were synthesized by the condensation of 3,5-dichloro-salicylaldehyde, 3-bromo-5-chloro-salicylaldehyde, and 3,5-dibromo-salicylaldehyde with isatin monohydrazone, respectively. The synthesized compounds were characterized by elemental analysis, 1H-NMR, FT-IR, UV-Vis spectroscopy, and mass spectrometry technique. For studied molecules, chemical parameters like frontier orbital energies, energy gap, electronegativity, chemical potential, chemical hardness, softness, electrophilicity, nucleophilicity, electrodonating power, electroaccepting power, polarizability, and dipole moment were calculated and discussed. Investigating the validity of well-known electronic structure principles like Maximum Hardness, Minimum Polarizability, and Minimum Electrophilicity Principles in the study, it was determined which compound is more stable compared to others. In recent days, a new software having PRIMorDIA name was developed to explore reactivity and electronic structure in large biomolecules by some of the authors of this paper. Molecular docking studies for these newly synthesized molecules were performed using PRIMorDIA software. Considering the intramolecular interactions, NBO analyzes of three bishydrazone derivatives were conducted to evaluate the chemical behavior.

Conceptual DFT based electronic structure principles in a dynamical context

Within the context of quantum fluid density functional theory diverse processes simulating a chemical reaction like interaction of an atom or a molecule with an externally applied electric or magnetic field or its collision with a proton have been analyzed in a dynamical situation. The changes produced in the chemical reactivity parameters namely chemical potential, hardness, polarizability during such processes have been identified and discussed. In addition, confinement is also introduced to observe the necessary variation in the different reactivity parameters.

Two empirical formulae for estimating standard entropy of inorganic ionic solids and a possible connection between two associated electronic structure principles

Two empirical formulae for estimating the standard entropies of some inorganic ionic solids are proposed. Linear relations are suggested between the standard entropy and the cube root of the formula unit volume as well as the cube root of the diamagnetic susceptibility, building a bridge between conceptual density functional theory and solid state chemistry. It is noted that the stabilities of inorganic ionic crystals are closely related to their molar diamagnetic susceptibilities. The suggested correlation provides a connection between the maximum entropy and minimum magnetizability principles.

Reactivity Dynamics.

The chemical reactivity of a molecule as a whole or of an atom in a molecule varies during a chemical reaction. A variation of global and local reactivity descriptors in the course of a physicochemical process was studied within a quantum fluid density functional theory framework. Effects of a physical confinement and the electronic excitation therein were studied. In this Perspective, we also highlight the direction of a spontaneous chemical reaction in the light of the dynamical variants of the conceptual density functional theory-based electronic structure principles. An exhaustive state-of-the-art dynamical study is warranted in order to understand a chemical reaction from a reactivity perspective augmenting the associated molecular reaction dynamics analysis.

Diversities in the chelation of aroylhydrazones towards cobalt(II) salts: Synthesis, spectral characterization, crystal structure and some theoretical studies

Five cobalt complexes synthesized from two aroylhydrazones were characterized by elemental analyses, thermogravimetric analysis, molar conductivity, magnetic susceptibility measurements, IR and electronic spectra. Single crystal X-ray structure of one of the complex is also reported and it got crystallized in triclinic space group P1¯ and the crystal structure shows a distorted octahedral geometry around the metal center. Spectral data reveal that both the aroylhydrazones are tridentate and coordinate through the azomethine nitrogen, hydrazonic oxygen, and pyridyl nitrogen. Magnetic susceptibility measurements confirm the paramagnetic nature of the Co(II) complexes and one of the complex was found to be diamagnetic in nature. Additionally, HF/6-311G(d,p)/LANL2DZ calculations were performed to predict the possible intramolecular interactions contributing to the lowering of the stabilization energy. Accordingly, π→ π* transitions were found to be responsible for the stabilization energy for the ligands and their cobalt complexes. To describe and discuss the chemical reactivity and stability of synthesized complexes, quantum chemical parameters like frontier orbital energies, hardness, softness, energy gap, electronegativity, chemical potential, electrophilicity, polarizability and dipole moment were calculated. Also, the main electronic structure principles such as maximum hardness, minimum polarizability, and minimum electrophilicity principles were considered to evaluate the stability of the complexes.

Conceptual density functional theory based electronic structure principles.

In this review article, we intend to highlight the basic electronic structure principles and various reactivity descriptors as defined within the premise of conceptual density functional theory (CDFT). Over the past several decades, CDFT has proven its worth in providing valuable insights into various static as well as time-dependent physicochemical problems. Herein, having briefly outlined the basics of CDFT, we describe various situations where CDFT based reactivity theory could be employed in order to gain insights into the underlying mechanism of several chemical processes.

Mixed ligand copper(II) chelates derived from an O, N, S- donor tridentate thiosemicarbazone: Synthesis, spectral aspects, FMO, and NBO analysis

Five new copper(II) chelates [(Cu(bmct))2] (1), [Cu(bmct)(phen)] (2), [Cu(bmct)(bipy)] (3), [Cu(bmct)(4,4′-dmbipy)] (4) and [Cu(bmct)(5,5′-dmbipy)] (5) with 5-bromo-3-methoxysalicylaldehyde-N(4)-cyclohexylthiosemicarbazone (H2bmct) as the chelating ligand and 1,10-phenanthroline, 2,2′-bipyridine, 4,4′-dimethylbipyridine, 5,5′-dimethylbipyridine as coligands have been synthesized and characterized by different physicochemical techniques like CHNS analysis, molar conductivity and magnetic studies, IR, UV/Vis and EPR spectral studies. In all the complexes, the thiosemicarbazone exists in thioiminolate form and coordinates to the metal through azomethine nitrogen, thioiminolate sulfur, and phenolate oxygen. EPR spectra in polycrystalline state at 298 K showed that compounds 1, 4, and 5 are isotropic, 2 is axial and 3 is rhombic in nature. In DMF at 77 K, compound 1 showed hyperfine lines in the parallel and perpendicular regions as well as superhyperfine lines due to the interaction of copper center with azomethine nitrogen of the ligand. Complex 2, in which g||>g⊥> 2.0023 suggests a distorted square pyramidal structure. To analyze the stability of the complexes, quantum chemical parameters like hardness, softness, polarizability, electrophilicity, electronegativity, and dipole moment were calculated and discussed within the framework of electronic structure principles known as Maximum Hardness, Minimum Polarizability and Minimum Electrophilicity Principles. Besides, the intramolecular donor–acceptor interactions for all complexes were evaluated by using NBO analysis. All calculations proved that Compound 3 is the most stable chelate among them.

Creating Competitive Active Sites on CNTs Walls by N‐Doping and Sublayer Co4N Encapsulating for Efficient Hydrogen Evolution Reaction

AbstractAn excellent catalyst can be effectively designed by adjusting its electronic structure. In this paper, an efficient hydrogen evolution reaction (HER) catalyst, carbon nanotubes with N doping and sublayer Co4N encapsulating (N−CNTs@Co4N) supported on Ni foam (NF), was designed and prepared through a complementary electronic structure principle. The as‐prepared N−CNTs@Co4N@NF catalyst shows outstanding hydrogen evolution activity in 1.0 M KOH solution. DFT calculation indicated that carbon nanotubes wall of N−CNTs@Co4N@NF catalyst provided more competitive catalytic active sites for hydrogen evolution reaction than N doped CNTs and Co4N singly. The greatly improved catalytic ability was owing to the redistribution of electron density for N−CNTs after Co4N embeds in, leading to a moderate absorption energy of H. This study demonstrated the successful rational design and experimental verification on developing a novel non‐noble metal catalyst.

Ligand stabilized transient “MNC” and its influence on MNC → MCN isomerization process: a computational study (M = Cu, Ag, and Au)

A theoretical investigation of the binding ability of different ligands [L = CO, H2O, H2S, N2, NH3, 1,3-dimethylimidazole (DMI), C2H2 and C2H4] with metal isocyanide and cyanide (MNC and MCN; M = Cu, Ag, Au) compounds has been carried out using quantum chemical computations. In order to analyze the thermochemical stability of these complexes, we have calculated the changes in the related dissociation energies and free energies by considering different possible dissociation pathways (four two-body and one three-body) such as (a) LMCN(/NC) = L + MCN(/NC); (b) LMCN = LM + CN; (c) LMCN = L + M + CN; (d) LMCN = LM+ + CN−; and (e) LMCN = L− + MCN+. The possible dissociation processes are endothermic in nature at room temperature suggesting non-spontaneity at 298 K. Our inspection suggests that MNC have higher binding ability than the MCN compounds in all of the L-bonding cases and both of them follow similar trends as Au > Cu > Ag. The natural bond orbital analysis, topological analysis of the electron density from atoms in molecules technique, and energy decomposition analysis have been carried out to characterize the nature of interaction between L and MCN which shows that the L‐M bonds acquire some degree of covalent character. Furthermore, in order to check the validity of the conceptual DFT-based electronic structure principles like maximum hardness and minimum electrophilicity principles, the change in the relevant global reactivity descriptors like chemical hardness (η), chemical potential (μ), and electrophilicity index (ω) is also studied along the isomerization path, LMNC → LMCN.

Quantum Monte Carlo study of the electron binding energies and aromaticity of small neutral and charged boron clusters.

The valence electron binding energies and the aromaticity of neutral and charged small boron clusters with three and four atoms are investigated using a combination of the fixed-node diffusion quantum Monte Carlo (FN-DMC) method, the density functional theory, and the Hartree-Fock approximation. The obtained electron binding energies such as the adiabatic detachment energy, vertical detachment energy, adiabatic ionization potential, and the vertical ionization potential are in excellent agreement with available experimental measurements. Their decomposition into three physical components such as the electrostatic potential and exchange interaction, the relaxation energy, and the electronic correlation effects has allowed us to determine that the neutral boron clusters are stabilized by the electrostatic and exchange interactions, while the anionic ones are stabilized by the relaxation and correlation effects. The aromaticity is studied based on electronic structure principles descriptor and on the resonance energy. The FN-DMC results from the electronic structure principles of the energy, hardness, and eletrophilicity have supported the aromaticity of , , and B4 and partially supported the aromaticity of the clusters B3, , and . The obtained values for the resonance energy of the clusters , B3, , B4, , and are 55.1(7), 54.2(8), 33.9(7), 84(1), 67(1), and 58(1) kcal/mol, respectively. Therefore, the order of decreasing stability of the trimer is , while for the tetramer it is , which is in agreement with the results from the molecular orbital analysis.

Favorable Direction in a Chemical Reaction Through the Maximum Hardness Principle

Recently, an assessment regarding the validity of maximum hardness principle has been done taking 34 exothermic chemical reactions (Poater, J.; Swart, M.; Solà, M. J. Mex. Chem. Soc. 2012, 56, 311) in which only 46% and 53% of the total reactions have greater hardness for the products and the reactants than those for the reactants and the transition states, respectively. They have also mentioned that a larger set of reactions should be studied to draw a general conclusion regarding the validity of maximum hardness principle. We have noticed that the reactions having fewer number of reactants than that of products and / or very hard atoms like H, N, O, F or very hard molecules like H2, N2, HF, HCN, CH4, etc. appearing in the reactant side, are more likely to disobey maximum hardness principle. In addition, dependence of hardness values on level of theory, basis sets, definitions, formulas, approximations should be kept in mind before criticising the validity of maximum hardness principle. Since these electronic structure principles are qualitative in nature, one should not expect them to be valid in all cases.

Role of Lithium Decoration on Hydrogen Storage Potential

Hydrogen storage potential of two sets of lithium containing systems, viz., Li-doped borazine derivatives and various bondstretch isomers of Li3Al4 - is studied at the B3LYP/6-311+G(d) level of theory occasionally supplemented by the results from the associated MP2/6-31+G(d) calculations. Negative values of interaction energy, reaction enthalpy, reaction electrophilicity, and desorption energies for the gradual hydrogen-trapping processes justify the efficacy of these systems as the hydrogen storage material. Presence of Li as well as aromaticity improves the situation. Various conceptual density functional theory based reactivity descriptors like electronegativity, hardness, and electrophilicity and the associated electronic structure principles such as the principles of maximum hardness and minimum electrophilicity lend additional support

The nucleophilicity equalization principle and new algorithms for the evaluation of molecular nucleophilicity

In this work, we have attempted to explore whether the nucleophilicity equalization principle can be conceived analogous to the well-established electronegativity, hardness, and electrophilicity equalization principle. Based on our new definitions of hardness and electronegativity and relying upon the geometric mean principle we proposed a new electronic structure principle, namely the nucleophilicity equalization principle. This approach provides a unified and useful procedure to calculate the nucleophilicity of molecules and groups assuming that nucleophilicity equalization principle is operative and justifiably valid. The results shown here indicate a close resemblance between theory and experiment.