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 iPr5 )2] 18d by the Guzei method 37 (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. 17 Linear coordination has only been observed when using the Cp iPr5 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, 38 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, which may be assigned to the fluxionality of the Cp ttt ligands. 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 rings. Determination of the solution magnetic moment of 2 by the Evans' NMR method 41 led to a value of 1.5 B, which agrees relatively well with that of 1.7 B expected for one unpaired electron in a d shell. The experiment value should yet be regarded as a lower limit given the high sensitivity and reactivity of 2. 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 N2 (Figures ). Recording the EPR spectrum of 2 at lower temperature (105 K) in a frozen pentane solution did not result in a better resolved spectrum. 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 iPr5 )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.