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Introduction of four tBu groups into a carbazol-ylframework leads to switching of the metal–ligand bonding inthe Ln(II) and Ca complexes from σ to π. Complexes [(tBu4Carb)2Ln] (Ln = Sm, Eu, Yb, Ca)are amido analogues of metallocenes, which adopt the sandwich structureswith parallel disposition of the aromatic ligands and strong contributionof η3-mode into η5metal–ligandbonding. The DFT calculations demonstratedthat the geometry is due to steric effects (presence of the bulky tBu groups) as well as the maximization of the overlap betweenthe Sm 4f orbital and the π-type nitrogen lone pairof the carbazol-yl ligand. Coordination of DME to the metal centersin [(tBu4Carb)2M] (M = Sm,Yb) results in the heterolytic dissociation of the metal–ligandπ-bond and the formation of ionic complexes [tBu4Carb–]2[Ln2+(DME)n]. [ABSTRACT FROM AUTHOR]