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Controlling the Dipole–Dipole Interactions between Terbium(III) Phthalocyaninato Triple-Decker Moieties through Spatial Control Using a Fused Phthalocyaninato Ligand

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journal contribution
posted on 02.12.2013, 00:00 by Takaumi Morita, Keiichi Katoh, Brian K. Breedlove, Masahiro Yamashita
Using a fused phthalocyaninato ligand to control the spatial arrangement of TbIII moieties in TbIII single-molecule magnets (SMMs), we could control the dipole–dipole interactions in the molecules and prepared the first tetranuclear TbIII SMM complex. [Tb­(obPc)2]­Tb­(Fused-Pc)­Tb­[Tb­(obPc)2] (abbreviated as [Tb4]; obPc = 2,3,9,10,16,17,23,24-octabutoxyphthalocyaninato, Fused-Pc = bis­{72,82,122,132,172,182-hexabutoxytribenzo­[g,l,q]-5,10,15,20-tetraazaporphirino}­[b,e]­benzenato). In direct-current magnetic susceptibility measurements, ferromagnetic interactions among the four Tb3+ ions were observed. In [Tb4], there are two kinds of magnetic dipole–dipole interactions. One is strong interactions in the triple-decker moieties, which dominate the magnetic relaxations, and the other is the weak one through the fused phthalocyaninato (Pc) ligand linking the two triple-decker complexes. In other words, [Tb4] can be described as a weakly ferromagnetically coupled dimer of triple-decker Tb2(obPc)3 complexes with strong dipole–dipole interactions in the triple-decker moieties and weak ones through the fused phthalocyaninato ligand linking the two triple-decker complexes. For [Tb4], dual magnetic relaxation processes were observed similar to other dinuclear TbIIIPc complexes. The relaxation processes are due to the anisotropic centers. This is clear evidence that the magnetic relaxation mechanism depends heavily on the dipole–dipole (f–f) interactions between the Tb3+ ions in the systems. Through a better understanding of the magnetic dipole–dipole interactions obtained in these studies, we have developed a new strategy for preparing TbIII SMMs. Our work shows that the SMM properties can be fine-tuned by introducing weak intermolecular magnetic interactions in a controlled SMM spatial arrangement.