LAUSR

The chemical nature of the ligand-unsupported gold(I)–lanthanide(III) bond in the proposed [LnIII(η5-Cp)2][AuIPh2] (Ln–Au; LnIII = LaIII, EuIII, or LuIII; Cp = cyclopentadienide; Ph = phenyl) models is examined from a theoretical viewpoint. The covalent bond-like Au–Ln distances (Au–La, 2.95 Å; Au–Eu, 2.85 Å; Au–Lu, 2.78 Å) result from a strong interaction between the oppositely charged fragments (ΔEintMP2 > 600 kJ mol–1), including the aforementioned metal–metal bond and additional LnIII–Cipso and C–H···π interactions. The Au–Ln bond has been characterized as a chemical bond rather than a strong metallophilic interaction with the aid of energy decomposition analysis, interaction region indicator, and quantum theory of atoms in molecules topological tools. The chemical nature of the Au–Ln bond cannot be fully ascribed to a covalent or an ionic model; an intermediate situation or a charge shift bond is proposed. The [AuIPh2]− anion has also been identified as a suitable lanthanide(III) emission sensitizer for La–Au and Lu–Au.