Fluorescence EXAFS of MgCl2-Supported Titanium Trichloride

XAS and XES Techniques Shed Light on the Dark Side of Ziegler–Natta Catalysts: Active‐Site Generation

“…In the resulting TiMg bimetallic salt the Ti sites have a +4 oxidation state and show a 6-fold coordination, [12] as monitored by DR UV-Vis, XANES and Kβ-XES spectroscopy ( Figure 2). In particular: i) the intense absorption around 25000 cm -1 in the DR UV-Vis spectrum ( Figure 2a) is assigned to fully allowed Cl(p)→Ti(d) ligand-tometal charge-transfer transitions, where the excited electron is associated with one of the nearest Cl anion and the transferred electron goes into a 3d orbital of the Ti 4+ ion; [14,[27][28][29][30] ii) the weak pre-edge peak at 4970.6 eV (shoulder at 4968.3 eV) in the XANES spectrum (Figure 2b), that precedes the absorption edge at 4979 eV, is due to 1s→pd transitions; [14,[31][32][33][34] iii) the two Kβ″ lines present in the vtc-XES spectrum (Figure 2c) at 4947 and 4953 eV are due to transitions mainly involving molecular orbitals having primarily O(2s) and Cl(3s) character, and thus identify the presence of oxygen and chlorine ligands in the first coordination sphere of the Ti sites. [35][36][37] The catalysts were obtained from the above mentioned precatalyst upon interaction with the AlR3 activator.…”

“…In particular, a sharp feature is observed at 4980 eV (having a shoulder at 4977 eV), which was assigned to allowed Ti(1s) → Cl(4p) transitions, enhanced by the multiple scattering contributions characteristic of well crystalline materials. [32,33,42] These features are absent in the XANES spectrum of the catalyst, suggesting that the multiple scattering contributions are limited. This observation is again in favor of a lowdimensional TiClx phase.…”

Apports historiques du rayonnement synchrotron

“…5 Dans mes investigations pour trouver des complexes de coordination utiles comme composés modèles afin de tester la théorie et de pouvoir analyser la structure de composés inconnus par XAS, Roger Fourme m'a suggéré de contacter un professeur de chimie de l'université Paris Sud à Orsay, Olivier Kahn. Je ne le connaissais ni de réputation, ni par ses travaux sur le magnétisme moléculaire.…”