Luminescence de complexes plan-carrés de nickel(II), palladium(II) et platine(II): une histoire d’interactions intermoléculaires, de pression et de température variable

This thesis focuses on the luminescence of square-planar complexes of nickel(II), palladium(II), and platinum(II) in solid-state. A comprehensive and quantitative understanding of less-explored effects of the luminescence properties, such as variation of structure, metal, and intermolecular interactions, is obtained based on experimental spectra. The emission spectra are assigned as d-d electronic transitions from the first excited triplet to the ground state singlet for all complexes studied. Application of simple theoretical models allows one to study and compare their electronic structures. Luminescence spectra are measured and compared for many complexes with bidentate ligands and the same ligator atoms, mostly in the dithiocarbamate family. Pressure and temperature variations are applied to gain further quantitative information on these effects, contrasting with current studies reported in the literature measured at only one set of conditions. Structural data is obtained by X-ray crystallography and correlated with the luminescence spectra, showing important spectroscopic effects for even subtle structural variation. These effects have a defining influence on the energy and the shape of the luminescence spectra as conditions are varied, allowing a quantitative characterization and comparison among a family of complexes. The different molecular structures and intermolecular packings allow us to characterize the effects of the metal centers, of structural variations, and of M…H-C intermolecular interactions. Among examples in the literature, it is seen that the nature of the metal affects significantly the luminescence spectra, for instance in the intensity. However, detailed comparisons of a series with 3d, 4d, and 5d metals are rare, the intensity of emission of 3d metal complexes often being poor. In this thesis, detailed comparisons between similar complexes with 3d, 4d, and 5d metals are presented, revealing intrinsic characteristics responsible for differing luminescence properties. Other studies have shown that the metal affects greatly the emission energy, especially for complexes showing metal-metal intermolecular interactions. This aspect is also studied but for the metal involved in M…H-C interactions, bringing crucial information to the understanding of the differences.  In this work, structural variations including and beyond metal-ligand bond compression are explored for molecular complexes at variable conditions instead of the more thoroughly studied inorganic salts. The effect of structural variations induced by temperature for the luminescence spectra is presented for a square-planar complex of platinum(II). The impact of the variation of the L-M-L angle as the structure changes with temperature or pressure is discussed, comparing the experimental results with those from the angular overlap model (AOM), equivalent to ligand-field theory and well adapted to the study of d-d transitions. Those characterizations supported by experimental evidence are new additions to structural variation considerations, as they are not usually taken into account in studies in the literature. M…H-C interactions are increasingly reported in the literature, and are present in some square-planar complexes with a d8 metal center. Being luminophores, the systematic comparison of the effect of these interactions on luminescence properties is performed for the first time in this thesis. By using luminescence spectroscopy at variable pressure, quantitative trends have been extracted to rationalize the relative strengths of such interactions. Other factors, such as alignment and possibility of movement of the interacting atoms, as well as the effect of deuteration, are revealed to be crucial to the characterization of the interaction. Luminescence spectroscopy at variable pressure as an experimental approach allows sensitive characterization of intramolecular and intermolecular structural changes, detecting even subtle variations in the weak M…H-C interactions. Results from this method are more direct and conclusive than those from vibrational spectroscopy at variable pressure. Thus, luminescence spectroscopy at variable pressure constitutes a promising method to gain experimental data on less-well characterized intermolecular interactions.

Keyphrases: Palladium(II), Nickel(II), Luminescence spectroscopy, Square-planar complexes, d8 electronic configuration, Platinum(II), Variable pressure, Variable temperature, M...H-C intermolecular interactions, Deuteration effect