Determination of the (17)O Quadrupolar Coupling Constant and of the (13)C Chemical Shielding Tensor Anisotropy of the CO Groups of Pentane-2,4-dione and beta-Diketonate Complexes in Solution. NMR Relaxation Study.
13C NMR relaxation times T(1) of the carbonyl groups of pentane-2,4-dione and beta-diketonate complexes Al(acac)(3) and Zr(acac)(4) (acac: pentanedionate anion) were measured for various magnetic field strengths, allowing a determination of the contribution of the chemical shift anisotropy mechanism to the total relaxation. NOE and T(1) measurements for the (13)C nucleus of the central methine carbon furnished the correlation time tau(c) for the reorientation of theses species. The chemical shift tensor anisotropy Deltasigma could be deduced and compared to the values obtained in the solid state. The quadrupolar coupling constant (QCC) of the (17)O nucleus could also be determined by measuring the line width of the (17)O NMR signal and using the tau(c) value. QCC values for the complexes are in the same range as for the pentane-2,4-dione molecule, indicating similar electronic distribution and symmetry around the oxygen atom of these different species. Deltasigma for the complexes are close together, and the values obtained in solution are approximately those obtained in the solid state. They are close to the value reported in the literature for tetraacetylethane, which can be considered as a dimer of a beta-diketone, but slight differences are observed for the individual components of the chemical shielding tensor.
Champmartin
D.
D
Laboratoire d'Etude des Systèmes Organiques et Colloïdaux, UA CNRS No. 406, Institut Nancéien de Chimie Moléculaire, Université Henri Poincaré-Nancy I, BP 239-54506 Vandoeuvre-lès-Nancy Cédex, France.
Rubini
P.
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