Supramolecular Approach for Enhancing Single-Molecule Magnet Properties of Terbium(III)-Phthalocyaninato Double-Decker Complexes with Crown Moieties

A Tb^III-phthalocyaninato double-decker ([1]⁰) single-molecule magnet (SMM) having four 15-crown-5 moieties in one of the ligands was synthesized, and its dimerization and magnetic properties were studied in an attempt to utilize the supramolecular aggregation for enhancing the SMM properties. Aggregation of [1]⁰ to form [1₂K₄]⁴⁺ in the presence of K⁺ ions was studied by using UV/Vis-NIR absorption and NMR spectroscopies. For the magnetic measurements, [1]⁰ and [1₂K₄]⁴⁺ were dispersed in poly(methyl methacrylate) (PMMA). UV/Vis-NIR absorption measurements on the PMMA dispersed samples were used to track the formation of [1₂K₄]⁴⁺. Direct current (DC) magnetic susceptibility measurements revealed that there were ferromagnetic Tb–Tb interactions in [1₂K₄]⁴⁺, whereas there was no indication of ferromagnetic interactions in [1]⁰. Upon the formation of [1₂K₄]⁴⁺ from [1]⁰ and K⁺ ions, the temperature at which the magnetic hysteresis occurred increased from 7 to 15 K. In addition, the area of magnetic hysteresis became larger for [1₂K₄]⁴⁺, meaning that SMM properties of [1₂K₄]⁴⁺ are superior to those of [1]⁰. Alternating current (AC) magnetic measurements were used to confirm this observation. Magnetic relaxation times at 2 K increased 1000-fold upon dimerization of [1]⁰ to [1₂K₄]⁴⁺, demonstrating the effectiveness of using K⁺ ions to induce dimer formation for the improvement of the SMM properties.