Influence of the Nature of the Ligands on the Electronic Ground State of Organouranium(V) Compounds, Studied by Electron Paramagnetic Resonance.
Organouranium(V) amide compounds were studied by electron paramagnetic resonance in frozen solution. Their g-tensors were quantitatively interpreted by assuming that dialkylamide, C(8)H(8), C(5)H(5), C(5)Me(5), and THF ligands interact only weakly with 5f orbitals of the central U(V) atom, so that the total angular momentum J = 5/2 remains a good quantum number for the description of the electronic ground state of these complexes (weak-field approximation). In the absence of THF ligands, the ground state is predominantly made of |M(J)()| = (1)/(2) states, with a significant admixture of |M(J)()| = (5)/(2) states independent of the symmetry of the complex. Thus 5f orbitals are essentially nonbonding, and the metal ligand bonding should involve mainly uranium 6d orbitals. A THF ligand induces a significant admixture of |M(J)()| = (3)/(2) states. Substitution of amide ligands by alkoxide ligands is characterized by strong U(V)(5f)-OR interactions, which breaks the weak-field approximation. This sensitivity to oxygen ligands indicates that 5f orbitals contribute to the U(V)-oxygen bonding.
Gourier
Didier
D
Service de Chimie Moléculaire, DRECAM, DSM, CNRS URA 331, CEA Saclay, 91191 Gif sur Yvette, France.
Caurant
Daniel
D
Berthet
Jean Claude
JC
Boisson
Christophe
C
Ephritikhine
Michel
M