A Route to Enhanced Energy Barriers and Reduced Magnetic Relaxation in Axial Bis(stannolediide) Lanthanidocenates

We report the synthesis and magnetic properties of one-dimensional lanthanidocenate coordination polymers, [Ln(η5-LSn)2K]n (Ln = Tb, Dy; LSn = [1,4-bis(tert-butyl-dimethylsilyl)-2,3-bis-phenyl-stannolediide]). These were obtained by abstracting the solvent molecules from the potassium atoms of the corresponding monomers [Ln(η5-LSn)2K(thf)4]. The flexible coordination of the stannole dianion enables polymerization via potassium-mediated Sn–K–arene interactions, yielding linear chain structures while preserving a highly axial coordination environment around the Ln3+ center. Magnetic studies reveal that both [Ln(η5-LSn)2K]n (Ln = Tb, Dy) compounds behave as single-molecule magnets in zero field, with significantly enhanced performance compared to their monomeric analogues. In particular, [Dy(η5-LSn)2K]n exhibits an increased effective energy barrier of Ueff = 1812 K, representing an improvement of ∼20%, alongside suppressed quantum tunneling of magnetization and slower relaxation dynamics. Detailed analysis of the relaxation mechanisms indicates that polymerization reduces spin–phonon coupling, as evidenced by a marked suppression of the Raman relaxation process, despite softer lattice vibrational modes. Ab initio calculations confirm the retention of highly axial electronic structures. These results demonstrate that assembling axial lanthanidocenate units into one-dimensional frameworks is an effective strategy to enhance magnetic anisotropy and control relaxation pathways, providing a route to mitigate relaxation in high-performance lanthanide-based single-molecule magnets.