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.C-60) was prepared by assembling (C60-Ih)[5,6]fullerene (C-60) 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 (phi) was determined to be 3.62 degrees. On the other hand, the two Tb3+ sites of 1.C-60 are not equivalent. The phi values for sites Tb1 and Tb2 were determined to be 3.67 degrees and 33.8 degrees, respectively, due to a change in the coordination symmetry of 1 upon association with C-60. At 1.8 K, 1 and 1.C-60 undergo different magnetic relaxations, and the changes in the ground state affect the spin dynamics. Although 1 and 1.C-60 relax via QTM in a zero applied magnetic field (H), H dependencies of the magnetic relaxation times (tau) for H>1500 Oe are similar. On the other hand, for H<1500 Oe, the tau values have different behaviors since the off-diagonal terms (Bkq;q not equal 0 ) affect the magnetic relaxation mechanism. From temperature (T) and H dependences of tau, 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 C-4 rotation axis and the spin dynamic properties in dinuclear Ln(3+)-Pc multiple-decker complexes.