Search

A detailed analysis of the C(sp3)−H activation process by vinylidene AuI complexes is described based on an intrinsic bond orbital analysis. Based on our analysis this event can be divided into three phases: (i) hydride transfer, (ii) C−C bond formation, and (iii) σ to π rearrangement of the lone pair coordinated to Au. Small perturbations of the system lead to either a concerted asynchronous reaction, or a stepwise reaction featuring an intermediate with a C-H-C three-centre two-electron (3c–2e) bond. The role of π-donating substituents is highlighted and provides a way of controlling reactions of this type in future experimental studies.

In this study, we report the substituent effect on the structures, frontier orbital analysis, and spectroscopic properties (IR, 13C, 29Si NMR) in the molybdenum silylidyne complexes CpMo(CO)2(≡Si-para-C6H4X) (X = H, F, Cl, CN, NO2 , Me, OMe, NH2 , NHMe) using MPW1PW91 quantum chemical calculations. The calculated structural parameters and spectral parameters are compatible with the experimental values in similar complexes. The nature of the chemical bond between the [Cp(OC) 2Mo]− and [Si-para-C6H4X]+ fragments was explored with energy decomposition analysis (EDA). The percentage composition in terms of the defined groups of frontier orbitals for CpMo(CO)2(≡Si-para-C6H4X) complexes was investigated to explore the character of the metal–ligand bonds. The linear correlations between the properties and Hammett constants (σ p) were illustrated. Natural bond orbital analysis (NBO) was used to illustrate the electronic structure of the complexes.

Cu–S heteroadamantanes are of great interest owing to their relevance to bioproteins. New copper(I) thiolate compounds with additional N-donor functions from phenanthroline ligands have been synthesised. These complexes feature heteroadamantane cage structures with minor deviations in their construction and, therefore, a strong structural relationship. Furthermore, a decanuclear copper–sulfur cluster complex was isolated and shows known structural motifs arranged in a new fashion. Metallothioneins are natural counterparts to these complexes due to their thiolate-rich and polynuclear d10 character. In addition to the structural characterisation, theoretical studies with a triple-zeta basis set have been performed to further understand the building patterns of the reported complexes and their relevance to copper-rich metalloproteins. This includes a Wiberg bond analysis and a full orbital analysis of selected heteroadamantanes to highlight the bonding interactions that connect the copper–sulfur skeletons.

In this comprehensive study on unsaturated phosphorus compounds of the type R-P=CR2, R-P=N-R, and R-P=P-R, we investigated how the electronic, spectroscopic, and geometric parameters are influenced by different substituents by means of ab initio and DFT methods. The parent systems are studied with highly accurate theoretical methods and used to benchmark DFT methods. The substituent effects are rationalized based on orbital analysis of DFT calculations for phos-phaalkenes, iminophosphanes, and diphosphenes in comparison with their analogous alkenes and imines. Theoretical data are also compared to experimental data if available. This study provides a broad picture of the use of DFT methods for unsaturated main group systems. Trends obtained from this study will enable a rational molecule design for selective manipulation of electronic and geometric properties.

The binding behaviors of eight bivalent metalloporphyrins (MPs) (MZn, Mg, Cu, Mn, Fe, Co, Ni, and Cd) with NH3 were investigated by density functional theory. For both MPs and corresponding complexes MPs-NH3, good linear correlations are found between the partial charge on metal M and that on atom N (nitrogen of porphyrin) as well as the MN bond length. Natural population and frontier orbital analysis demonstrate that charge transfer in CoP-NH3 is much easier and greater. As a consequence of the charge transfer and the hybridization of molecular energy levels, striking disparities of electronic properties of MPs-NH3 are observed. Particularly, a modest linear relationship is obtained between the magnitude of charge transfer and the binding energy. The much greater Fukui functions of CoP, together with its larger binding strength, suggest that CoP is more favorable to the interaction with NH3, which might be a promising sensing material to response NH3. © 2013 Wiley Periodicals, Inc.

Equivalence restrictions usually imposed on the Hartree-Fock approximation are removed by letting one of the 2p radial functions be different from the others. Two energy minima are found both with a single Slater-type atomic orbital basis and with a more extended basis. One minimum corresponds to the one diffuse-electron model and the other to the one tight-electron model. Although two wave functions based on these two models look different, the natural orbital analysis shows they are close to each other as a many-electron wavefunction. The calculation is further extended by using N radial functions for an N-electron atom. The results with the single Slater-type atomic orbital basis are presented and are discussed.

Six groups of diastereomeric 2,4-disubstituted adamantanes were studied with DFT–GIAO–NBO (natural orbital analysis) methods. The calculated 13C chemical shifts reproduce well the experimental data. It was found that among all diastereomers, those bearing substituents in δ-syn-axial positions showed the largest overall deshielding, i.e. the sum of all 13C chemical shifts [Σδ(13C)] was the greatest and also had the highest delocalization contribution to the molecular energy evaluated with NBO. The higher delocalization energy is proposed to be the origin of the deshielding δ-syn-axial effect. Copyright © 2008 John Wiley & Sons, Ltd.

The reactions of 1-pentenyl decomposition system have been studied extensively at the B3LYP/6-311++G∗ ∗ level with Gaussion 98 package. The potential energy surface with zero-point energy correction was drawn. All reaction channels were fully investigated with the vibrational mode analysis, frontier orbital analysis and electron population analysis to confirm the transition states and reveal the reaction mechanism.

In this work, we present a theoretical study (based on DFT-calculations) of the electronic properties of compounds crystallising in a NH4Pb2Br5 type structure in a wide pressure range. The main focus of this study is to elucidate the nature of bonding of the ns2-cations at ambient and elevated pressure. For a better understanding of the structure and bonding, the DOS of these compounds are evaluated and discussed on the basis of a simple model assuming mainly ionic interactions. The calculations are complemented by an orbital analysis using the crystal orbital Hamilton population (COHP) and an analysis of the electronic density topology with the electron localisation function (ELF). Structural and theoretical investigations give results that are in excellent agreement: The DFT-calculations confirm the existence of bonding interactions between the ns2-cations at elevated pressure. Our study indicates that the “character” of the additional electron pair changes with increasing pressure from nonbonding to bonding in agreement with a simple model system of two interacting ns2-cations. Hochdruckuntersuchungen an Verbindungen mit NH4Pb2Br5-Struktur Teil II: Elektronische Struktur und ihre Anderung unter hohem Druck Auf der Basis von DFT-Rechnungen werden theoretische Untersuchungen an Verbindungen, die im NH4Pb2Br5-Strukturtyp kristallisieren, in einem grosen Druckbereich durchgefuhrt. Das Hauptziel dieser Untersuchungen ist die Charakterisierung des Bindungszustandes der ns2-Kationen bei niedrigem und hohem Druck. Zum besseren Verstandnis der Struktur dieser Verbindungen und der Bindungssituation, wird die Zustandsdichte dieser Verbindungen anhand eines einfachen Modells diskutiert, das vorwiegend ionische Wechselwirkungen postuliert. Die Rechnungen werden durch Analysen der COHP und der Topologie der Elektronendichte mit der Elektronenlokalisierungsfunktion (ELF) vervollstandigt. Theoretische Untersuchungen und die Auswertung experimenteller Daten liefern Ergebnisse, die sehr gut miteinander ubereinstimmen: Die DFT-Rechnungen bestatigen die Existenz bindender Wechselwirkungen zwischen nah benachbarten ns2-Kationen bei hohem Druck. Der Charakter des zusatzlichen Elektronenpaares am ns2-Kation andert sich also von nahezu nichtbindend zu bindend in Ubereinstimmung mit einem einfachen Modellsystem fur zwei miteinander wechselwirkende ns2-Kationen.

We performed density functional calculations to examine the intermolecular self-interaction of metal tetraauride MAu(4) (M = Ti, Zr, and Hf) clusters. We found that the metal auride clusters have strong dimeric interactions (2.8-3.1 eV) and are similar to the metal hydride analogues with respect to structure and bonding nature. Similarly to (MH(4))(2), the (μ-Au)(3) C(s) structures with three three-center two-electron (3c-2e) bonds were found to be the most stable. Natural orbital analysis showed that greater than 96 % of the Au 6s orbital contributes to the 3c-2e bonds, and this predominant s orbital is responsible for the similarity between metal aurides and metal hydrides (>99 % H 1s). The favorable orbital interaction between occupied Au 6s and unoccupied metal d orbitals leads to a stronger dimeric interaction for MAu(4)-MAu(4) than the interaction for MH(4)-MH(4). There is a strong relationship between the dimeric interaction energy and the chemical hardness of its monomer for (MAu(4))(2) and (MH(4))(2).

A recently developed Full Configuration Interaction method is discussed and used to compute wave functions for N2 and H8 on an IBMRISC 6000 workstation. As a further application of the formalism a cluster and natural orbital analysis of the wave functions is performed for the N2 molecule at various internuclear distances and for the H8 model. © 1993 John Wiley & Sons, Inc.

Extended Huckel band calculations, frontier crystal orbital analysis, and degenerate-level perturbation theory are used to evaluate the effect inclusion of bulk-layer interactions has on the relative stabilities of ordered overlayers. Five patterns of hydrogen atoms chemisorbed on unreconstructed graphite (11% coverage) are examined for the Bernal (ABABAB...) and registered (AAA...) three-dimensional stackings. The single-layer two-dimensional approximation for graphite is found not to be entirely satisfactory for the type of chemisorption pattern stability questions addressed in this paper