Luis Enrique Sansores

Electronic structure of Ge3N4 possible structures

Experiments have shown that Ge3N4 is a promising material for application in photodiodes, amplifiers, optic fibers, protective coatings, etc., and several experimental studies have been carried out on this material, however, only one theoretical study has been reported in the literature about β-Ge3N4. In this work we present a systematic study of the structural properties and electronic structure of five possible structures of Ge3N4. The phases under study are the α, β, cubic, pseudocubic, and graphitic. The analysis shows that the hardest is the cubic with a bulk modulus B=232.5 GPa, while the α and β have the same bulk modulus (B=219.8 GPa). The pseudocubic and graphitic phases are the softest with B=147.0 and 61.7 GPa, respectively. The band structure shows that the α, β, cubic, and pseudocubic have an indirect band gap while the graphitic has a direct band gap. Total energy considerations indicate that the β phase is the most stable while the graphitic is the less stable one. Charge density analysis is also included.

Benzene fused five-membered heterocycles. A theoretical approach

The Nuclear Independent Chemical Shift of each ring, as a criterion of aromaticity, is used to explain the stability order of benzopyrrole, benzofuran and benzothiophene, and their isomers. The results indicate that the benzene ring is aromatic in all the systems. The five-membered rings of benzopyrrole, benzofuran and benzothiophene are also aromatic, whereas those of isobenzopyrrole, isobenzofuran and isobenzothiophene are non-aromatic. This could be an explanation of the stability of the former molecules. The molecular orbitals and the condensed Fukui functions derived from the electronic structure calculations are also reported. These reactivity indices explain the expected electrophilic substitution of these compounds. The theoretical structure, ionization energies, order of aromaticity, stability and reactivity are in good agreement with the experimental results. The usefulness of this approach to determine the reactivity is discussed since their stability and reactivity may be understood. The reactivity indices are useful to explain and confirm the experimental information, and for molecules with unknown reactive behavior, this approach could help to predict some of the reactions.

Theoretical study of the novel sandwich compound [Au3Cl3Tr2]2+

AbstractA theoretical study of a sandwich compound with a metal monolayer sheet between two aromatic ligands is presented. A full geometry optimization of the [Au3Cl3Tr2]2+ (1) compound, which is a triangular gold(I) monolayer sheet capped by chlorines and bounded to two cycloheptatrienyl (Tr) ligands was carried out using perturbation theory at the MP2 computational level and DFT. Compound (1) is in agreement with the 18–electron rule, the bonding nature in the complex may be interpreted from the donation interaction coming from the Tr rings to the Au array, and from the back-donation from the latter to the former. NICS calculations show a strong aromatic character in the gold monolayer sheet and Tr ligands; calculations done with HOMA, also report the same aromatic behavior on the cycloheptatrienyl fragments giving us an insight on the stability of (1). The Au –Au bond lengths indicate that an intramolecular aurophilic interaction among the Au(I) cations plays an important role in the bonding of the central metal sheet. Figure(a) Ground state geometry of complex 1; (b) Top view of compound 1 and Wiberg bond orders computed with the MP2/B1 computational method; (c) Lateral view of compound 1 and NICS values calculated with the MP2/B1 method; the values in parenthesis were obtained at the VWN/TZP level

Amorphous clusters I. Electronic structure of Si clusters with N, P and As dopants

Amorphous impurity clusters of the type XSi 20 H 28 with X = N, P and As have been studied using the well-known pseudopotential SCF Hartree-Fock method (and the HONDO Program). The local electronic density of states and charge density contours have been obtained. It is found that the covalent nature of the bonding in undoped silicon is altered by the presence of the dopants and both an ionic component and a shielding effect appear when N, P and As are substituted in the center of the amorphous cluster. Also, the local density of states in the neighborhood of a Si atom, nearest neighbor to the center of the cluster, indicates the presence of a new p-state in the band gap. There are quantitative differences in the electronic structure of the clusters as a function of the dopants. These results are analyzed in the light of the local changes and their relevance to the amorphous solid state properties.

Theoretical study on the series of [Au3Cl3M2] complexes, with M = Li, Na, K, Rb, Cs

AbstractThe prediction of the series of complexes [Au3Cl3M2] with M = Li, Na, K, Rb and Cs, has been achieved at the ab initio level of theory. All geometries were fully optimized at the MP2 level of theory; the central Au3 cluster is capped by chlorine atoms and the alkaline metals lie above and below the plane of the central ring; aurophilic interactions were found on the metal cluster, and also a strong aromatic character coming from the delocalized d-electrons of the Au atoms according to nuclear independent chemical shift calculations. On the other hand, the chemical hardness parameter was used to test the stability of the series of complexes, and the Fukui indexes of electrophilic and nucleophilic attack were employed to explore possible sites where chemical reactivity may play a role. FigureMolecular representations of the series of complexes [Au3Cl3M2] (M = Li, Na, K, Rb, Cs) and their corresponding chemical hardness

A theoretical study of the interaction of hydrogen and oxygen with palladium or gold adsorbed on pyridine-like nitrogen-doped graphene.

The interaction of H2 and O2 molecules in the presence of nitrogen-doped graphene decorated with either a palladium or gold atom was investigated by using density functional theory. It was found that two hydrogen molecules were adsorbed on the palladium atom. The interaction of these adsorbed hydrogen molecules with two oxygen molecules generates two hydrogen peroxide molecules first through a Eley-Rideal mechanism and then through a Langmuir-Hinshelwood mechanism. The barrier energies for this reaction were small; therefore, we expect that this process may occur spontaneously at room temperature. In the case of gold, a single hydrogen molecule is adsorbed and dissociated on the metal atom. The interaction of the dissociated hydrogen molecule on the surface with one oxygen molecule generates a water molecule. The competitive adsorption between oxygen and hydrogen molecules slightly favors oxygen adsorption.

Electronic structure of C40 possible structures

Abstract C40 is a fullerene with a conformation that has been proposed as Td, D2d, D4h and D5d symmetry groups. The correct structure has not been determined because it has not been possible to isolate the molecule, but there have been several studies of minor fullerenes that include it. In this work we present a theoretical study at the gaussian 94 HF/3-21G level that gives answers about the principal differences between the mentioned structures and the possible thermodynamic stability of each one. Furthermore, we include a similar study on the new D2h structure that we propose.

Aromaticity in cyanuric acid

This study analyzes the aromatic nature of cyanuric acid (hexahydrotriazine) and some of its derivatives, in terms of aromatic stabilization energy (ASE) and electronic behavior. The simplest molecule (C3N3O3H3) is the most aromatic item out of the entire set, but some of the others also display aromatic character. The structure of all the rings is analyzed considering their molecular orbitals as well as studying the inductive effect.

Five and nine membered (heteronines) heterocyclic molecules. Theoretical approach

Abstract The presence or absence of aromaticity in nine membered heterocyclic molecules (heteronines) has been studied from a theoretical point of view (B3LYP/6-311G(2d,p) level). For comparison, the aromaticity of pyrrole, thiophene and furan was analysed. The aromaticity of azonine and thionine is well established along with the problems that arise from the stabilisation of the latter. The origin of oxonine non-aromaticity is discussed in terms of atomic charges and electronegativity. Results for the ion cyclononatetraenide are also reported. Reaction coordinates leading to thionine derivatives are studied. Condensed Fukui functions derived from electronic structure calculations were computed for five and nine membered heterocyclic molecules. These reactivity indices explain the observed products with electrophiles. The stability and the reactivity of these molecules may be understood in terms of the present results.

Manganese (I) complexes of p-xylene and [2n] cyclophanes from a theoretical sight

Abstract Theoretical B3LYP/6-311G** calculations were performed in order to understand the electronic structure and the structural behavior of bis( p -xylene) and bis([2,2]- p -cyclophane) manganese (I) complexes. The minimum energy configuration of bis( p -xylene) has D 2 d symmetry while that of bis([2,2]- p -cyclophane) has D 2 symmetry. The energy difference between the D 2 d and the D 2 h structures for both compounds is small. The results of the calculation for the pseudorotational barrier indicate that a process of interconversion may be possible. A comparison between experimental and theoretical infrared spectra was done for bis( p -xylene) Mn(I). Theoretical and experimental spectra are in good agreement. For both compounds, the HOMO has a big contribution from the metal orbital. In bis([2,2]- p -cyclophane) manganese (I) the HOMO and HOMO-1 form a bridge between the rings, this can explain some of the electric flow. Much of the evidences that we present in this work, indicates that transannular electronic interaction for bis([2,2]- p -cyclophane) manganese (I) is present.