Influence of Peripheral Substitution on the Magnetic Behavior of Single-Ion Magnets Based on Homo- and Heteroleptic TbIII Bis(phthalocyaninate).

A series of homoleptic ([Tb^III(Pc)₂]) and heteroleptic ([Tb^III(Pc)(Pc′)]) Tb^III bis(phthalocyaninate) complexes that contain different peripheral substitution patterns (i.e., tert-butyl or tert-butylphenoxy groups) have been synthesized in their neutral radical forms and then reduced into their corresponding anionic forms as stable tetramethylammonium/tetrabutylammonium salts. All of these compounds were spectroscopically characterized and their magnetic susceptibility properties were investigated. As a general trend, the radical forms exhibited larger energy barriers for spin reversal than their corresponding reduced compounds. Remarkably, heteroleptic complexes that contain electron-donor moieties on one of the two Pc ligands show higher effective barriers and blocking temperatures than their homoleptic derivatives. This result is assigned to the elongation of the NTb distances in the substituted macrocycle, which brings the terbium(III) ion closer to the unsubstituted Pc, thus enhancing the ligand-field effect. In particular, heteroleptic [Tb^III(Pc)(Pc′)] complex 4, which contains one octa( tert-butylphenoxy)-substituted Pc ring and one bare Pc ring, exhibits the highest effective barrier and blocking temperature for a single-molecule magnet reported to date. [ABSTRACT FROM AUTHOR]