A. Le Beuze

Experimental and theoretical study of organic corrosion inhibitors on iron in acidic medium

Abstract The corrosion inhibition on metallic iron surfaces by organic molecules has been investigated both experimentally and theoretically. The inhibition efficiency of thiophenol, phenol and aniline have been compared through gravimetric and electrochemical experiments. From EH–MO and EH-tight-binding calculations, it has been possible to compare the strength of the bonding interaction between the inhibitors and the metal, with and without the presence of adsorbed protons on the metal surface, and to provide a rationalization of their different efficiencies.

Theoretical solvent effects on molecular structure and spectroscopic properties through the virtual-charge model. Application to the inverted solvatochromy of benzophenone n → π* and π → π* absorption bands

Abstract Non-specific solvent effects have been introduced within the virtual-charge model of Constanciel and Tapia: the definition of solvatons for a reference state allows us to apply this method to the study of all states (ground and excited) of the molecule. This model, which has been developed here within the CNDO/S scheme, allows a quantitative evaluation of solvatochromy of electronic transitions. Moreover, relationships between bond lengths and bond population indexes are used to describe geometrical variations upon solvation. The calculations are applied to the study of solvent effects on the molecular structure and the n → π * and π → π * absorption bands of the benzophenone molecule. The results of the model are in good agreement with solvent-dependent experimental data and it can possibly be used when the experimental approach is difficult.

Comparaison des effects electroniques des ligands a deux electronx CX (X = O, S, Se) dans des complexes organometalliques du type CH3CO2(C6H5)Cr(CO)2(CX)

Abstract Structural and spectroscopic (IR, Raman) results concerning the organometallic complexes, CH 3 CO 2 (C 6 H 5 )Cr(CO) 2 (CX) (X = O, S, Se) and theoretical calculations allow the comparison of electronic effects of CO, CS and CSe ligands. The strenght of the ligandmetal bond and the overall electron-with- drawing ability are higher for Se than for S and O, the largest variation being between S and O. This overall effect results in better σ-electron-repelling and π-electron-withdrawing abilities for Se than for S and O. Consequences of substituting one CO by CS or CSe in CH 3 CO 2 (C 6 H 5 )Cr(CO) 3 are analyzedin terms of molecular coordination. In particular Cr(CO) 2 (CS) deformations and CrC (ring) bond variation are discussed. Some comparisons are made with phosphinechromium complexes.

Electronic structure of Chevrel Phases: Emphasis on the part played by the cluster twisting angle through a LCAO-EHT tight binding study

Abstract The electronic structure of PbMo6S8 has been investigated using the so-called EHT-tight-binding method. An idealized cubic and an experimental distorted geometry are used, with standard atomic orbital parameters and diagonal H-matrix elements. A full band structure is presented in the idealized case. In both cases, the density of state curves computed using an integration over the Brillouin zone are also presented. The results show the importance of the twisting angle on the electronic structure near the Fermi level.

Structure cristalline et moleculaire du benzoate de methyle chrome dicarbonyle trifluorophosphine. Mise en evidence d'une courte liaison chrome phospore

Abstract The crystal and molecular structure of dicarbonyltrifluorophosphine chromium methylbenzoate has been determined by a single crystal X-ray study. The compound crystallizes with two molecules per unit cell in the space group P 1 . The structure has been refined to R and R″ values of 0.068 and 0.067 respectively, for 1434 independant reflexions having I> 3;σ(I). The molecular structure, compared with those of some derivatives of the type CH3CO2(C6H5)Cr(CO)2L, is intermediate between those corresponding to L = PPh3 and L = CO. The Cr—P distance (2.132(3) A), is the shortest of all the known chromium(0)—trivalent phosphorus distances, suggesting that the PF3 ligand is a good π-electron acceptor.

Electronic structure of ZrNi4P2 and related compounds with ZrFe4Si2-type structure

Extended Huckel molecular orbital and tight-binding band structure calculations have been performed on ZrNi 4 P 2 and then applied through a rigid band model to related compounds with the same ZrFe 4 Si 2 -type structure. The electronic structure has been built up step by step, from fragments, in order to obtain a better understanding of the main interactions which govern the evolution of the lengths of the metal-metal bonds and the lattice cohesion. The role of the 3d metal electron count and that of the ligand matrix are displayed and discussed

Variation of R in the isocyanide series RNC: As an example of the concept of controlled modifications of the properties of ligands for organometallic synthesis

Abstract Basically different behavior inside a homogeneous series of two-electron ligands can be predicted using simple concepts; for example, π-back donation onto RNC: ligands may be dramatically increased with respect to classical alkyl isocyanides by interaction with a carbonyl group in a position α to the nitrogen. Organometallic complexes of Cr(O) bearing such N-acylisocyanides ligands have been prepared and studied, From both the electronic and structural points of view, isocyanide ligands allow a wider scope of application in comparison with CO and CS.

Linear dependence ofXα eigenvalues on occupation number application to the determination of the ligand field integrals

A linear relation between theXα eigenvalues and the occupation number of the ligand field states in CrCl4 is established and used to calculate mono- and bimolecular integrals of ligand field interest. A formula for calculating 10 Dq and Koide-Pryces parameter (ε) from theXα eigenvalues is given. The method is generalized for anydN system.

Hyperpolarizabilities of substituted benzene molecules: MNDO calculations

The γ values for a series of substituted benzene molecules of the H-C6H4-R and R-C6H4-R′ types (R, R′=H, CH3, OCH3, CHO, CN, COOH, F, Cl, Br, I, OH, NO2, NO, NH2, NHMe, N(Me)2, Li, CF3, NHNH2, NHOH, C2H, COCN, COF, SO3H, phenyl, vinyl, cyclopropenyl, cyclo-pentadienyl) have been computed using the finite perturbation method at the MNDO level. Our results are compared to experimental data and to other theoretical values. A classification of the various substituting groups is set up so as to help in the design of new optically interesting molecules. It has been shown that the pCCB (para-Cyclopropenyl, Cyclopentadienyl Benzene) presents a large hyperpolarizability γ value (61.54 10−36 esu) compared with γ (C6H6)=0.72 10−36 esu.

Electronic structure of the pseudo-one-dimensional superconductor Tl2Mo6Se6 according to SCF scattered-wave Xα computations

Abstract The electronic structure of Tl 2 Mo 6 Se 6 has been investigated using the Xα cluster approach. The ground-state eigenvalues show that the Fermi level lies in a single degenerated band which supports the experimental results. Contour maps show the anisotropic character of the wawe functions of this Fermi level. The metal-metal and metal-selenides interactions have been discussed.