Single-Molecule Magnets Based on Heteroleptic Terbium(III) Trisphthalocyaninate in Solvent-Free and Solvent-Containing Forms.

Binuclear heteroleptic triple-decker terbium(III) phthalocyaninate (Pc)Tb[(15C5)₄Pc]Tb(Pc), where Pc²⁻ is phthalocyaninate dianion and 15C5 is a 15-crown-5 moiety, has been synthesized as a solvent-free powder (1) and a well-defined crystal solvate with o-dichlorobenzene (Pc)Tb[(15C5)₄Pc]Tb(Pc)⋅6C₆H₄Cl₂ (2). In the crystal structure of 2, the Tb-N(Pc) distances to the nitrogen atoms in the outer and inner decks are 2.350–2.367(4) and 2.583–2.598(4) Å, respectively, and the Tb–Tb distance is 3.4667(3) Å. The twist angle between the outer and the inner decks is 42.6°. The magnetic properties were studied for both 1 and 2. The χ_MT magnitude of 23.3 emu⋅K/mol at 300 K indicates a contribution of two Tb^III centers with the ⁷F₆ ground state. The χ_MT product increases with decreasing temperature to reach 38.5 emu⋅K/mol at 2 K. This is indicative of ferromagnetic coupling between Tb^III spins in accordance with previous data for triple-decker lanthanide phthalocyaninates of a dipolar nature. Both forms show a single-molecule magnet (SMM) behavior manifesting the in-phase (χ′) and out-of-phase (χ″) AC susceptibility signals in an oscillating field of 3 Oe with estimated effective spin-reversal energy barriers (U_eff) of 222(9) and 93(7) cm⁻¹ for 1 and 2, respectively. The compounds show narrow hysteresis loops in the −1 – +1 kOe range, and the splitting between the zero-field-cooling and field-cooling curves is observed below 6 K. Thus, in spite of similar static magnetic characteristics, each form of the Tb(III) complex shows a different dynamic SMM behavior. [ABSTRACT FROM AUTHOR]