| Abstract
| - The molecular structures of tris(dipivaloylmethanato)neodymium(III), Nd(dpm)3, and tris(dipivaloylmethanato)ytterbium(III), Yb(dpm)3 have been determined by gas electron diffraction (GED) and quantum chemical calculations (DFT). Both molecules were found to have D3 molecular symmetry. A comparison of the length and strength of Ln−O bonds in the Ln(dpm)3 complexes and the solid cubic sesquioxides Ln2O3 is given.
- The molecular structures of tris(dipivaloylmethanato)neodymium(III), Nd(dpm)3, and tris(dipivaloylmethanato)ytterbium(III), Yb(dpm)3, have been determined by gas electron diffraction (GED) and structure optimizations through densityfunctional theory (DFT) calculations. Both molecules were found to have D3 molecular symmetry. The most importantstructure parameters (ra structure) are as follows (GED/DFT): Nd−O = 2.322(5)/2.383 Å, Yb−O = 2.208(5)/2.243Å, O−Nb−O = 72.1(3)/71.3°, and O−Yb−O = 75.3(2)/75.8°. The twist angles of the LnO6 coordination polyhedron,defined as zero for prismatic and 30° for antiprismatic coordination, were θ = 19.1(3)/14.2° for Nd and 20.4(2)/19.2° for Yb. Structure optimizations of La(dpm)3, Gd(dpm)3 Er(dpm)3, and Lu(dpm)3 by DFT also yielded equilibriumstructures of D3 symmetry with bond distances of La−O = 2.438 Å, Gd−O = 2.322 Å, Er−O = 2.267 Å, andLu−O = 2.232 Å. The Ln−O bond distances in 12 Ln(dpm)3 complexes studied by GED decrease in a nearlylinear manner with the increasing atomic number (Z) of the metal atom, as do the Ln−O bond distances in thecubic modifications of 14 sesquioxides, Ln2O3. The bond distances in the dpm complexes are, however, about 2%shorter. The mean Ln−O bond rupture enthalpies of the cubic sesquioxides calculated from thermodynamic datain the literature vary in an irregular manner with the atomic number; the La−O, Gd−O, Tb−O, and Lu−O bonds arenearly equally strong, and the remaining bonds are significantly weaker. The Ln−O bond rupture enthalpies previouslyreported for 11 Ln(dpm)3 complexes are on the average 13 kJ mol-1 or about 5% smaller than in the sesquioxides,but they vary in a similar manner along the series: it is suggested that the pattern reflects variations in the absoluteenthalpies of the gaseous Ln atoms.
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