Datensatz

Zusammenfassung

Single-crystal cryogenic X-ray diffraction at 6 K, electron paramagnetic resonance spectroscopy, and correlated electronic structure calculations are combined to shed light on the nature of the metal–tris(aryloxide) and η²–H, C metal–alkane interactions in the [((^t·BuArO)₃tacn)U^III(^Mecy-C6)]·(^Mecy-C6) adduct. An analysis of the ligand field experienced by the uranium center using ab initio ligand field theory in combination with the angular overlap model yields rather unusual U–O_ArO and U–N_tacn bonding parameters for the metal–tris(aryloxide) interaction. These parameters are incompatible with the concept of σ and π metal–ligand overlap. For that reason, it is deduced that metal–ligand bonding in the [((^t·BuArO)₃tacn)U^III] moiety is predominantly ionic. The bonding interaction within the [((^t·BuArO)tacn)U^III] moiety is shown to be dispersive in nature and essentially supported by the upper-rim ^tBu groups of the (^t·BuArO)₃tacn^3– ligand. Our findings indicate that the axial alkane molecule is held in place by the guest–host effect rather than direct metal–alkane ionic or covalent interactions.