Études spectroscopiques expérimentales et théoriques de complexes de métaux de transition

The main goal of this thesis is to study the electronic structure of different transition metal complexes using spectroscopic methods. The detailed knowledge of the electronic structure helps to understand and develop new materials, new synthesis methods as well as new theoretical models.  Usually, the information gathered from spectra of a single compound is not sufficient to identify the most important influences determining its electronic structure.  Historically, in order to collect more information on transition complexes, series of similar compounds with the same metal center and oxidation state and varying ligands have been explored.  This approach allows some trends that are directly related to the electronic structure of the metal center to be identified.  The changes induced on the electronic structure by the ligand modifications are often larger than desired.  We want to study continuous variations of the electronic structure specific to one compound with an experimental method that only slightly perturbs the structure.  Hydrostatic pressure, as reported in the literature, modifies the electronic structure sufficiently to change UV-visible absorption, luminescence and Raman spectra.  The changes are revealing electronic information on the compound.  In order to analyze these experiments, we are using electronic structure and nuclear dynamics calculations.  In this thesis, we explore the electronic structure of molybdenum(IV), platinum(II) and palladium(II) complexes.  In chapter 3, we observe a +12 cm-1/kbar shift of the luminescence band from trans-[MoOCl(CN-t-Bu)4]BPh4 between ambient pressure and 25 kbar.  The molybdenum(IV) metal ion in this complex has a 4d2 electronic configuration.  It is the first time that a positive pressure-induced shift of the d-d luminescence maximum is recorded for a metal-oxo complex.  On the same system, at higher pressure, the sign of the shift changes.  This behavior is due to the competition between the different ligands of this six-coordinate compound.  Density functional calculations are used to rationalize this phenomenon.  In chapter 4, we study palladium(II) and platinum(II) complexes having the same ligands.  The most important ligand for these complexes is 1,4,7-trithiacyclononane (ttcn).  At low pressure, this ligand is bidentate.  At high pressure, an additional antibonding interaction between the metal and the axial ttcn sulfur atom in the [Pt(ttcn)Cl2] complex modifies the nature of the HOMO orbital. This is illustrated by the measured red shift of the luminescence band maximum of -19 cm-1/kbar.  As in the molybdenum(IV) complex, the shift illustrates the competition in the electronic structure between all ligands.  The platinum(II)-sulfur axial interaction is the most plausible cause of the red shift.  On the other hand, the corresponding palladium(II) complex exhibits a blue shift of +6 cm-1/kbar.  In this case, the axial interaction does not appear to dominate the other interactions.  Again electronic structure calculations help to establishing a model that explains the observations from diff erent spectroscopic experiments. Chapter 5 presents a more detailed study of the electronic structure and the nuclear dynamics of palladium(II) and platinum(II) complexes having a simpler structure than the compounds in the previous chapters.  The first excited electronic state of these compounds exhibits a Jahn-Teller distortion.  We desire to establish a workflow for experimentalists to allow them to analyze spectra in which the Born-Oppenheimer approximation is not valid.  Time-dependent density functional theory is combined with the Heidelberg model for nuclear dynamics in order to study the non-adiabatic effects.  Our goal is to advance our knowledge of such effects on transition metal complexes.

Keyphrases: transition metal, inorganic chemistry, theory, spectroscopy, pressure, electronic, vibrational, density functional theory, diabatic, adiabatic