| Abstract
| - The 17O quadropolar couplingconstants and the 13C chemical shielding tensoranisotropies of carbonyl groups in β-diketonate complexes ofAl(III) and Zr(IV) ions were obtained in solution fromT1 NMR relaxation studies at different magneticfield strengths. The values were compared to those observed forpentane-2,4-dione and to those measured in the solid state. Theelectronic distribution in the CO groups of the enolate anioncoordinated to a cation was compared to that of the keto−enol form ofsome β-diketones.
- 13C NMR relaxation timesT1 of the carbonyl groups of pentane-2,4-dioneand β-diketonate complexes Al(acac)3and Zr(acac)4 (acac: pentanedionate anion) weremeasured for various magnetic field strengths, allowing adetermination of the contribution of the chemical shift anisotropymechanism to the total relaxation. NOE andT1 measurements for the 13C nucleusof the central methine carbon furnished the correlation timeτc for thereorientation of theses species. The chemical shift tensoranisotropy Δσ could be deduced and compared to thevalues obtained in the solid state. The quadrupolar couplingconstant (QCC) of the 17O nucleus could alsobedetermined by measuring the line width of the 17O NMRsignal and using the τc value. QCC values forthecomplexes are in the same range as for the pentane-2,4-dione molecule,indicating similar electronic distributionand symmetry around the oxygen atom of these different species.Δσ for the complexes are close together, andthe values obtained in solution are approximately those obtained in thesolid state. They are close to the valuereported in the literature for tetraacetylethane, which can beconsidered as a dimer of a β-diketone, but slightdifferences are observed for the individual components of the chemicalshielding tensor.
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