The lanthanide-centroid distance in 2-Tb is almost the same as in the terbocenium cation [Tb(Cp ttt )2] + (2.325(4) Å) but slightly shorter than in [Tb(Cp iPr5 )2] + (2.356(6) Å). This highlights the strong electronic influence of the dianionic stannole ring in axial positions, as despite the anticipated increase of the Ln-ligand distance due to steric bulk, the stannole is located in close proximity to the metal ion. The anionic [Ln(η 5 -L Sn )2] -motif is slightly bent with Ct-Ln-Ct angle of 154.3° for Dy and 153.5° for Tb. These values lie in the range of previously reported metallocene-type Dy and Tb cations. For example, the bis(stannolediide) compounds 2-Ln are slightly more linear than the Ln cations [Dy(Cp ttt )2] + (152.845(2)°), [Tb(Cp ttt )2] + (152.2(2)°) and [Dy(Cp iPr4 )2] + (147.2(8)°) but more bent compared to the bisphospholide Dy cation (157.94(4)°) and the bis-borolediide Dy anions (156.5°, 158.6(3)°, 161.4(3)°). The reactions of the K-bridged Tb(III) and Dy(III) complexes 2-Ln with 18-crown-6 allowed the abstraction of the K + ion and enabled the formation of the respective anionic sandwich complexes 3-Tb and 4-Dy (Fig. ). SCXRD analysis revealed that the molecular structures of 3-Tb and 4-Dy are charge-separated ion pairs. In the case of the Tb compound 3-Tb, red single crystals were formed from a concentrated benzene solution. The molecular structure of 3-Tb features the expected monoanionic homoleptic Tb(III) sandwich compound (Fig. ). The cationic part consists of a crown ether-solvated potassium cation, which is connected to the next K + unit via a bridging 18-c-6 molecule. In the anionic sandwich part, upon decoordination of the bridging K cation, the Ct1-Tb-Ct2 angle of 155.295( As the main driving force of the described synthesis was the exploration of the resulting magnetic properties of the Ln-sandwich complexes, we performed SQUID-magnetometric analyses on compounds 2-Ln (Ln = Tb, Dy), 3-Tb and 4-Dy. Based on previously reported systems and theoretical models of SMM performance, we expected to find complexes with relatively high Ueff and TB. Starting with the Tb(III) analogues 2-Tb and 3-Tb, applying an external magnetic field of 1000 Oe (0.1 T), we have observed room temperature values of the molar susceptibility temperature product χT of 12.48 and 11.07 cm 3 K mol -1 , respectively (Fig. ). For both samples, the values are within approximately 6 % deviation from the theoretical value of a single Tb(III) ion with J = 6 and gJ = 3/2 of 11.82 cm 3 K mol -1 . Such deviations can be ascribed to the preparation procedure, where slightly inaccurate determination of the sample mass in the glovebox can introduce error of a few percent very quickly. Upon cooling the samples down, χT decreases very slowly while above 100 K and starts decreasing more rapidly below that temperature. Interestingly, for 2-Tb the data below 100 K reveals a sort of plateau around 50 K followed by a sudden very strong drop below 10 K. On the other hand, 3-Tb shows a rather constant decrease in the temperature range of 100 K -2 K.