The ring planarity (sum of inner angles: 540.0°) and the similar C-C bond lengths within the SnC4 ring hints at the aromatic nature of the stannole dianion, and these bonding metrics are comparable to those of its lithium derivative. The 119 Sn NMR spectrum reveals a singlet at 615 ppm, which is shifted to higher frequencies in comparison to its dilithium analog (473 ppm). The bis-stannolediide lanthanide compounds [Ln(η 5 -L Sn )2K(thf)4] (2-Ln, Ln = Tb, Dy) were synthesized via salt metathesis from anhydrous LnI3 (Ln = Tb, Dy) and [K2(Et2O)0.45(η 5 -L Sn )] in 1:2 molar ratio in THF (Fig. ). After stirring the reaction mixture at room temperature for 16 h, the insoluble metathesis salt (KI) was filtered and the remaining THF solution was concentrated and layered with n-pentane. Dark red block-shaped crystals were obtained after two weeks, the mother liquid was decanted, and the crystals were dried under vacuum for 30 min, giving an overall yield of 47% for 2-Dy and 57% for 2-Tb, respectively. Single crystal X-ray diffraction analysis revealed the formation of the bis-stannolediide complexes, in which the potassium cation is η 1 -coordinated to the Sn lone pairs of both stannolediide rings (Fig. ). To complete the coordination sphere, four additional THF molecules are coordinated to the K ion. Both complexes are isostructural and crystallized in the monoclinic space group C2 with half of the molecule in the asymmetric unit, with the Ln•••K located at the crystallographic C2 axis. The Ln•••K distance of 5.3223(13) Å (2-Dy) and 5.3427(8) Å (2-Tb) are too long to represent any bonding interaction. As expected, the Ln ion is coordinated to the two stannole rings in η -mode and the torsion angle between the two stannole rings is about 31.0° in both complexes (Fig. ). The distance between the Ln and the centroid of the stannole ring is 2.3039 Å for 2-Dy and 2.3232 Å for 2-Tb. This difference is expected, as the Tb 3+ ion is slightly larger than the Dy 3+ ion. The lanthanide-centroid distance in 2-Dy is even shorter than the respective distances in the bis-phospholide complex (2.354(3) Å) and [Dy(Cp ttt )2] + (2.316(3) Å) but well-comparable to the values in other Dy metallocenium ions (2.244(6)-2.340(7)°).