Manipulation of the Coordination Geometry along the C₄ Rotation Axis in a Dinuclear Tb³⁺ Triple-Decker Complex via a Supramolecular Approach

A supramolecular complex (1⋅C₆₀) was prepared by assembling (C60-Ih)[5,6]fullerene (C₆₀) with the dinuclear Tb³⁺ triple-decker complex [(TPP)Tb(Pc)Tb(TPP)] (1: Tb³⁺=trivalent terbium ion, Pc²⁻=phthalocyaninato, TPP²⁻=tetraphenylporphyrinato) with quasi-D_4h symmetry to investigate the relationship between the coordination symmetry and single-molecule magnet (SMM) properties. Tb³⁺-Pc triple-decker complexes (Tb₂Pc₃) have an important advantage over Tb³⁺-Pc double-decker complexes (TbPc₂) since the magnetic relaxation processes correspond to the Zeeman splitting when there are two 4f spin systems. The two Tb³⁺ sites of 1 are equivalent, and the twist angle (φ) was determined to be 3.62°. On the other hand, the two Tb³⁺ sites of 1⋅C₆₀ are not equivalent. The φ values for sites Tb1 and Tb2 were determined to be 3.67° and 33.8°, respectively, due to a change in the coordination symmetry of 1 upon association with C₆₀. At 1.8 K, 1 and 1⋅C₆₀ undergo different magnetic relaxations, and the changes in the ground state affect the spin dynamics. Although 1 and 1⋅C₆₀ relax via QTM in a zero applied magnetic field (H), H dependencies of the magnetic relaxation times (τ) for H>1500 Oe are similar. On the other hand, for H<1500 Oe, the τ values have different behaviors since the off-diagonal terms ((Formula presented.)) affect the magnetic relaxation mechanism. From temperature (T) and H dependences of τ, spin-phonon interactions along with direct and Raman mechanisms explain the spin dynamics. We believe that a supramolecular method can be used to control the magnetic anisotropy along the C₄ rotation axis and the spin dynamic properties in dinuclear Ln³⁺-Pc multiple-decker complexes.