Ionization energies of metal chelates. Acetylacetonates, trifluoroacetylacetonates, and hexafluoroacetylacetonates of trivalent metals of the first transition series

Abstract

and is dedicated to him on the occasion of his 65th birthday JOHN B. WESTMORE, MARK L. J. REIMER, and CHARLES REICHERT. Can. J. Chem. 59, 1797Chem. 59, (1981.For several j3-diketonate complexes of metals of the first transition series the electron impact ionization efficiency curves obtained using unfiltered electron beams were fitted to empirical post-threshold ionization laws. In the energy region extending to 2-3 V above threshold, fits of high quality were obtained for a second power ionization law (i.e. ion current was proportional to the square of the electron energy in excess of the threshold energy) for complexes of AI(III), Sc(III), Mn(III), Fe(III), and Co(II1) (do, do, d4, d 5 , and d6, respectively). In the cases of Ti(III), V(III), and Cr(II1) complexes ( d l , d2, and d3, respectively) the experimental points lay above the "best fit" curves in the immediate post-threshold region. Electron energies were initially calibrated by fitting experimental data points for xenon to its published ionization functions. In later experiments, Al(tfa)3 or Al(hfa), was used for calibration purposes. When the electron impact results were compared with published photoelectron spectra of the complexes (where available) it became apparent that, in the threshold region, the strongest ionization processes involved electron removal from ligand dominated x orbitals. In the cases of Ti(III), V(III), and Cr(II1) complexes, weaker ionization processes involving electron removal from orbitals of predominantly metal 3d character (correlating with t , in octahedral symmetry) could also be detected at lower electron energies. (II1) ( d l , d 2 et etd3 respectivement), les points experimentaux de la loi restent au-dessus des courbes qui assurent une meilleure corklation dans la region immediate du post seuil. On a initialement calibre les Cnergies de l'klectron en inkrant les donnkes experimentales du xenon dans ses fonctions d'ionisation deja connues. Dans des experiences subsequentes, on a tente d'utiliser les complexes Al(tfa)3 ou Al(hfa), pour I'etalonnage. Quand on compare les resultats de I'impact electronique avec les spectres photoelectriques connus des complexes (quand ils sont disponibles), il devient apparent que dans la region du seuil, le processus d'ionisation le plus important fait intervenir I'enlevement de I'electron des orbitales x dominees par le ligand. Dans les cas des complexes de Ti(II1) de V(II1) et de Cr(III), des processus d'ionisation plus faibles impliquant I'enlevement d'un electron des orbitales B caracttre 3d metallique predominant (en accord avec t2, dans une symetrie octaedrique) peuvent aussi Ctre deceles a des plus faibles energies des electrons.[Traduit par le journal]

Photoelectron Spectroscopy of Bis(2,4-Pentanedione)−Oxovanadium(IV) [VO(acac)2] and Derivatives: Substituent Effects on the 2,4-Pentanedione Donor

“…Our spectrum of VO(acac) 2 is in general agreement with the previous report, 17 though our measured ionization energies differ slightly due to the use of symmetric Gaussians in the previous report, and by the improved resolution and precision of our experiment. The ionization assignments are consistent with reports for the free ligands, 31 and for other metal-acac analogues, [18][19][20]32,33 and can also be compared to the results from ab initio and density functional molecular orbital calculations (vide infra).…”

“…A linear relationship between ionization energies and pK a is also seen from the photoelectron data for other homoleptic complexes of acac and its derivatives. [18][19][20][21] There is a larger substituent effect upon the ligand-based ionizations of these systems than what is observed for the vanadyl complexes. Table 4 gives ionization energies for selected homoleptic complexes of acac and hfac.…”

“…The photoelectron spectra of these molecules are convenient probes for analyzing how the electronic structure throughout the molecules is affected by the substituents, because ionizations from orbitals primarily associated with the oxo lone pairs, metal d orbitals, and acac ligand-based orbitals are all clearly observed and identified. While the photoelectron spectra of many homoleptic acac complexes have been reported, − these molecules have not been as useful as these vanadyl complexes for studying the donor abilities of the acac ligands because the metal-based ionizations are typically obscured by the acac-based ionizations, and no other ancillary ligand ionizations are present. As will be shown, the relative donor abilities of these acac ligands as measured by the photoelectron spectroscopy of the metal complexes do correlate with the p K a of the free ligands.…”

Surface-Controlled Deposition of Sc2O3 Thin Films by Atomic Layer Epitaxy Using β-Diketonate and Organometallic Precursors

“…Alkoxides, aryloxides, and nonfluorinated and fluorinated − β-diketonates of scandium have been prepared. The nonfluorinated volatile β-diketonate compounds contain ligands such as acetylacetonate (acac), − 2,2,6,6-tetramethyl-3,5-heptanedione (thd), , 6-methyl-2,4-heptanedione (mdh), and 2,2,7-trimethyl-3,5-heptanedione (tmod) − and mixed-ligand cyclooctatetraene compounds , have also been synthesized.…”