Lanthanidocenes: Synthesis, Structure, and Bonding of Linear Sandwich Complexes of Lanthanides

The Article presents the synthesis, structure, and bonding of a series of neutral and linear sandwich compounds with the cyclo­nona­tetra­enyl (Cnt) ligand and divalent lanthanides. These compounds account for the emergence of the lanthan­idocene series in reference to the ferrocene and uranocene. The synthetic strategy uses the solubility difference between two conformational isomers of the ligand, as well as the isomerization of the compounds induced by solvent coordination, yielding the isomorphous and isostructural neutral and rigorously linear sandwich complexes. The molecular structures feature a Cnt–Ln–Cnt angle of 180° and a ring size close to the Cnt–Cnt­(centroid) distance. A qualitative molecular orbital diagram is provided, in D9d symmetry, and DFT calculations enforce the bonding model.