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Chemins réactionnels conduisant à la formation des oxydes des métaux de transition 3dn (n>5) : structure électronique des composés antiferromagnétiques M2O2 (M=Cr, Mn, Fe, Co, Ni, Cu)

Abstract : This thesis presents a strategy of calculation in order to study the oxides of the first series of transition metals with density functional theory. It is based on the validation of a computation method for a given system by best reproducing its experimental data, and then using this very method to complete our knowledge on the spectroscopic properties and the reactivity of the system. From the study by absorption spectroscopy of the rare gas matrix isolated products of the Ni, Ni2 + O2 reaction, we gathered a set of relevant experimental data on the NiO2 and Ni2O2 oxides. Concerning the former, about which there was some contradictory papers on the ground state of the eta-2 complex, we provided a general description of the reactivity quite consistent with the experimental conclusions. We also pointed out two kinds of pathways for the Ni insersion reaction to give ONiO, a thermal (from the reagents in their ground states) and a photochemical one. The case of Ni2O2 incited us to develop a particular method. This compound features an antiferromagnetic coupling with a non-zero spin density carried by each metal centre. To deal with this cases with a monoreference method, we developped a procedure in which a "Broken-Symmetry" calculation, followed by the analysis of the obtained contaminated wavefunction and the average value , gave us a criterion to adjust the HF exchange fraction in the hybrid functional to reproduce the experimental observations. This procedure has been used M2O2 on oxides (M=Cr, Mn, Fe, Co, Ni, Cu) and allowed use to observe the evolution of their properties from Cr to Cu. The antiferromagnetic singlet state was yielded for all case except Cu2O2. The antiferromagnetic interation between the two copper atoms is too weak to favorise the rhombic antiferromagnetic features with the other metals. We showed the the stability of these oxides is essencially due to the superexchange interaction between the metal centres and the diamagnetic ligand (O2-). In line with this scheme, we have established thanks to a topological analysis of local functions i.e. rho(r) and ELF, that these bimetallic dioxides must be considered as (M2+)2(O2-)2.
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Submitted on : Wednesday, October 17, 2007 - 4:08:54 PM
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  • HAL Id : tel-00126690, version 2

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Fayçal Allouti. Chemins réactionnels conduisant à la formation des oxydes des métaux de transition 3dn (n>5) : structure électronique des composés antiferromagnétiques M2O2 (M=Cr, Mn, Fe, Co, Ni, Cu). Autre. Université Pierre et Marie Curie - Paris VI, 2006. Français. ⟨tel-00126690v2⟩

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