Alain Sevin

Electron localization function comparative study of ground state, triplet state, radical anion, and cation in model carbonyl and imine compounds

The modifications of bonding in carbonyl and imine compounds upon excitation, electron attachment, and ionization were studied within the framework of the electron localization function (ELF). The topological analysis of ELF allows a partition of the molecular space into regions having a clear chemical meaning: the basins. The electronic populations of the basins associated with bonding and nonbonding character, as well as the basin spin densities, were calculated at the MP2 level of the quantum mechanical calculation. Good agreement was found with the classical view in terms of mesomeric structures corresponding to the dominant localization of electrons contained in frontier molecular orbitals (MOs). The variations of the basins population were compared to the predictions of MO theory. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 897–910, 1999

Substituent effects in polarized phosphaalkenes: a theoretical study of aminocarbene–phosphinidene adducts

The effect of substituent has been theoretically explored in the case of polarized phosphaalkenes formed with an aminocarbene and a phosphinidene. The shape of the experimentally characterized structures has been explained in terms of electronic and steric effects. The balance between σ-donation and π-back-donation as a function of the substituent has been explored by the use of electron localization function (ELF) analysis and correlated with the bond dissociation energy and geometrical structure. The aromaticity of the carbene ring, obtained by NICS calculation, has been achieved.

The nature of the chemical bonding in the D3h and C2v isomers of Fe3(CO)12

The bonding in the D3h and C2v isomers of Fe3(CO)12 has been studied with two complementary topological approaches, namely the atoms-in-molecules (AIM) theory and the analysis of the electron localization function (ELF). Both methods indicate that the stabilization of the C2v isomer is mostly due to the presence of two ligands in bridging positions, which take advantage of a rather large electron transfer from the iron atoms. Within the ELF framework, each of these latter ligands is involved in three-center (3c–4e) bonds with the two adjacent iron atoms.

Topological study, using a coupled ELF and catastrophe theory technique, of electron transfer in the Li+Cl2 system

A topological study of electron transfer in the {Li+Cl2} system, based on catastrophe theory and using ELF as a starting point, has been achieved. It enables the determination of the method-independent invariants that might be used for characterizing the well-documented harpooning process in all types of geometry. This study has shown that the process is characterized by an electron jump from the covalent {Li+Cl2} state, stable at large separation distances, to the ionic charge transfer state {Li++Cl2-}. The topological invariant associated with this behaviour is a dual cusp catastrophe, whose existence has been found at any level of calculation, that is, MP2, DFT and CASSCF. The latter catastrophe is mostly associated with the actual cleavage of the Cl2- species. Analysis of the topological parameters allows the actual regions of PES crossings, in any geometry, to be localized. Our results suggest that the dual cusp catastrophe characterizes the diabatic surface crossings that are subjacent in the classical adiabatic analysis of the overall reaction path.

Theoretical study of electrophilic versus nucleophilic character of transition metal complexes of phosphinidene

Abstract A comparative theoretical study of the terminal phosphinidene complexes HPCr(CO) 5 , HPTi(Cp 2 ) and HPTiCl 2 , at the MP2 and DFT levels, has been carried out. The calculated results have then been used for determining the electron localization function (ELF) in these moieties. Both techniques show that in the singlet ground state of HPCr(CO) 5 , one gets a weak double P–Cr bond, with an electrophilic character on P (i.e. electron-deficient center). Conversely, in the singlet ground state of Ti complexes, the P–Ti bond shows a greater double bond character than in the P–Cr linkage, associated with an overall nucleophilic character of P. These results are in good agreement with all available experimental data.

Determination of substitutional sites in heterocycles from the topological analysis of the electron localization function (ELF)

The topological analysis of the electron localization function ELF has been carried out on five‐membered (C4H4NH, C4H4PH, C4H4O, C4H4S) and six‐membered (C5H5N, C5H5P) heterocycles. The bonding in these molecules is discussed on the basis of the valence basin populations. It is shown that the values of the ELF function at the (3,−1) critical points between disynaptic basins related to a given center provide a criterion to determine substitutional sites.

A cyclobutadiene—palladium complex with a non-planar cyclobutadiene ring obtained from the palladium catalyzed dimerization of an ynamine

A cyclobutadiene—palladium complex, obtained by dimerization of an ynamine is described. The crystal structure of this compound shows, as salient feature, that the cyclobutadiene ring is not planar, but highly puckered. Anti-bonding interactions have been suggested as an explanation for this puckering.

A theoretical study of the bonding in NO, (NO)2, (NO)2− and (NO)22− using a topological analysis of the electron localization function

The topological analysis of the ELF function calculated at the DFT level for (NO)2, (NO)2− and (NO)22− reveals a regular variation in the NN bonding. In the neutral species, a very weak attraction results form the fluctuation of a small electron population associated with the N lone pairs. A similar but even weaker attraction is found between the O atoms, thus favouring the cis geometry. The same trends are found in the cis anion, although in the more stable trans isomer a NN bonding basin appears. The latter bonding basin is more pronounced in the dianions. The molecular orbital localization function (MOLF) method which is briefly described, is proposed for gaining information on the σ/π separation.

A THEORETICAL STUDY OF THE FORMATION OF STABLE ANION INTERMEDIATES VIA ELECTRON CAPTURE BY HETEROSUBSTITUTED THREE MEMBERED RING XCH2CY2 COMPOUNDS (X = O, S, NH, PH; Y = H, F)

Abstract A comparison has been made between the electron acceptor properties of various three membered ring molecules, XCH2CY2 (X = O, NH, S, PH; Y = H, F). In a first step, the emphasis has been put on the ability of these substrates to accommodate an extra electron in their lowest-lying antibonding (valence and diffuse) MOs (vertical anions). A strong dichotomy was found between compounds bearing a heteroatom of the second row and those bearing a heteroatom of the third row. For the second row heteroatoms, the electron was essentially located in the diffuse space attached to the H atoms, via the XH (σ∗) and CH2 (π∗) antibonding MOs; while for first row ones, it remained mainly located on the heteroatom, in a Rydberg + valence p-type MO. The open anions resulting from ring opening have then been studied. Two series of anions resulted: when F-substituents were present on the terminal carbon atom, a 1–3 dipolar structure was obtained, whereas the possibility of resonant forms was present when F-substituents were borne by the central C atom. The possibility of obtaining stable anionic species has finally been qualitatively examined.

An electron localization function study of the strain energy in carbon compounds

Abstract It is shown, through an electron localization function (ELF) analysis of the strain in carbon compounds, that, globally, the valence basins V(CH) and V(CC) tend to preserve a VSEPR (valence shell electron pair repulsion) geometry. This point is clearly illustrated by the valence attractors location. The properties of V(CC) basins, associated with the CC bonds, remain as constant as possible. The main effect of the strain is to modify the maximal electron localization in each V(CC) basin. This study points out once more the difficulty in relating global strain to local bond properties.