The molecular structure of 2 in the solid state (Figure ) displays two independent molecules of 2 in the asymmetric unit, featuring very similar metric data, and confirms the formation of a basefree bent metallocene complex. The two Cp ttt ligands are in an eclipsed arrangement, providing efficient kinetic stabilization of the Lu II metal center. A comparison of the steric shielding in 2 vs. that in [Lu(Cp i Pr5 ) 2 ] 17d by the Guzei method 36 (see Supporting Information for details) revealed very similar G values (83.5 and 85.5%, respectively). The bent arrangement in 2, which displays an average Cp(ctr)-Lu-Cp(ctr) (ctr = ring centroid) angle of 167.2°, is typical for Cp-based Ln II sandwich complexes. Linear coordination has only been observed when using the Cp i Pr5 ligand, which presents a higher symmetry and different steric profile than the Cp ttt ligand. In contrast to the previously reported [Ln(Cp ttt ) 2 ] (Ln = Sm, Eu, Yb, Tm) complexes, for which a monotonic contraction in the Ln-Cp(ctr) separation of ca. 0.018 Å is observed per atomic number increment, the average Lu-Cp(ctr) distance of 2.305 Å in 2 does not follow this trend (Figure ). Although there have been discussions regarding the model that should be best used to fit the variation in bond distances due to the lanthanide contraction, 37 the Lu-Cp(ctr) in 2 appears ca. 0.056 Å shorter as would be expected from a simple linear fit. The apparent decrease in ionic radius can be traced back to the 4f n 5d 1 (n = 14) configuration for Lu II , compared to the 4f n+1 configuration adopted by the divalent Sm, Eu, Yb and Tm congeners, and covalent interactions involving the populated 5d orbital. The 1 H NMR spectrum of 2 at room temperature displays two hardly identifiable broad resonances. Upon heating to 80 °C, a better-resolved spectrum can be obtained with two main resonances at  2.0 ( 1/2 ≈ 70 Hz) and 0.9 ppm ( 1/2 ≈ 200 Hz) in a respective 1:2 ratio, corresponding to the t Bu groups of freely rotating Cp ttt ligands. Continuous-wave X-band EPR measurements performed on a solution of 2 in pentane at room temperature only revealed one broad isotropic signal at g = 2.274 with unresolved hyperfine coupling, which disappeared upon addition of N 2 (Figures S34-35). In contrast, an eight-line EPR pattern was reported for [K(crypt)][LuCp' 3 ] ( 175 Lu, I = 7/2, 97.4% natural abundance), whereas [Lu(Cp i Pr5 ) 2 ] did not give rise to an observable signal. The geometry of complex 2 was optimized at the DFT level (B3W91 functional) and the optimized geometry compares well with the experimental one. In particular, the Lu-Cp(ctr) distance is well reproduced (2.335 vs. 2.305 Å experimentally) as well as the Cp(ctr)-Lu-Cp(ctr) angle (166.6° vs. 167.2° experimentally). The SOMO (Figure ) of 2 appears to be the metal d z 2 orbital, in line with a Lu II 4f 14 5d 1 configuration, and agrees with the isotropic g value of the EPR signal.