Calculated and Experimental Geometries and Infrared Spectra of Metal Tris-Acetylacetonates:  Vibrational Spectroscopy as a Probe of Molecular Structure for Ionic Complexes. Part I

Abstract

The geometries and infrared spectra of the trivalent metal trisacetylacetonate complexes (M[O2C5H7]3) (M = Sc, Ti, V, Cr, Mn, Fe, Co, Al) have been calculated using nonlocal hybrid density functional theory (DFT) with a split-valence plus polarization basis for the ligand and valence triple-ζ for the metal. These molecules are uncharged, which facilitates the calculations, but at the same time are fairly ionic, resembling biologically important metal complexes with “hard” ligands (O, N). DFT has been widely used to model such complexes, but very few rigorous comparisons have been performed for experimentally well-characterized model compounds. Vibrational spectra are very sensitive to molecular structure and thus constitute an adequate test of the theory. After a mild scaling correction, the calculated frequencies are in excellent agreement with the experimental fundamentals, and the predicted infrared intensities are qualitatively correct. The results allow an unambiguous assignment of the observed infrared spectra; some earlier assignments have been revised. Our results show that current routine theoretical techniques can predict accurate vibrational spectra for this class of compounds. In part I we focus on Fe, Cr, Sc, and Al tris-acetylacetonates; these are high-spin D3 complexes that are expected to present no Jahn−Teller distortion. (Ti, V, Mn, and Co tris-acetylacetonates are treated in part II.) Correlating calculated infrared spectra with experiment should lead to firm structural predictions in these difficult systems.

RETRACTED: Crystal structure of human apolipoprotein A-I: Insights into its protective effect against cardiovascular diseases

“…Refinement was tightly restrained, using noncrystallographic symmetry restraints, for the protein and Cr-acac3 moieties, in addition to normal geometric restraints. Geometric restraints for the Cr-acac3 moieties were derived from its crystal structure (48). Cross validation was performed throughout the refinement by computing free R values for 5% of the data, chosen randomly to cover the resolution range.…”

An Experimental and Theoretical Study of the Aluminium Species Present in Mixtures of AlCl3 with the Ionic Liquids [BMP]Tf2N and [EMIm]Tf2N

“…Comparable complexes with aluminium, for example, Al-A C H T U N G T R E N N U N G (acac) 3 (acac = acetylacetonate), are already known. [7][8][9] Related complexes of the rare-earth elements with [Tf 2 N] À as a ligand have also been reported, [5,[10][11][12][13] so it is plausible that the system AlCl 3 + [Tf 2 N] À should form similar compounds. The energetics of the overall reaction profile is given in Figure 2.…”

DFT calculations as a powerful technique to probe the crystal structure of Al(acac)3

“…All EFG and chemical shielding calculations were implemented using the Gaussian 98 package. [30] Among the different crystal structures of Al(acac) 3 , we used the more recent ones of the α and γ polymorphs determined at room temperature in our calculations [Refs [8,11] (molecule A)]. We did not use the most recent X-ray structures because they have not been carried out at room temperature as the NMR experiment has been.…”