Journal
JOURNAL OF PHYSICAL CHEMISTRY A
Volume 108, Issue 33, Pages 6893-6900Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jp048550x
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The structure and bonding in large complexes of actinide(III) and lanthanide(III) with tridentate N-donor ligands and water molecules have been investigated through quantum chemistry calculations in order to characterize the nature of the lanthanide-ligand and actinide-ligand bonds. Calculations have been performed using relativistic density functional theory on [M(L)(H2O)(6)](3+), [M(L)(H2O)(5)Cl](2+), and [M(H2O)(9)](3+) clusters where M = La, Ce, Nd, U, Pu, Am, or Cm and L = 2,2':6'2terpyridine (Terpy) or 2,6-bis(5,6-dimethyl-1,2,4-triazin-3-yl)pyridine (MeBtp). Calculated M-L distances compare well with X-ray crystal data obtained on related systems. In particular, calculations correctly reproduce the experimentally observed shortening of the uranium-ligand bond in comparison with the cerium-ligand bond. The calculated evolution of the M-L bond as a function of the cation shows that lanthanide-ligand distances decrease with the diminution of the ionic radius, whereas the actinide-ligand distances increase from uranium to americium and are shorter than Ln-N distances. These trends are explained by the presence of slightly stronger covalent effects in the metal-ligand bond for the actinides, decreasing in the order U > Pu > Am Cm, compared to lanthanides. The participation of 5f orbitals in the bonding is found to be significant only for uranium.
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