Controlling the dipole-dipole interactions between terbium(III) phthalocyaninato triple-decker moieties through
Takaumi Morita1, Keiichi Katoh, Brian K Breedlove
1Department of Chemistry, Graduate School of Science, Tohoku University , 6-3 Aramaki-Aza-Aoba, Aoba-ku, Sendai, Miyagi 980-8578, Japan.
Abstract:
Using a fused phthalocyaninato ligand to control the spatial arrangement of Tb(III) moieties in Tb(III) single-molecule magnets (SMMs), we could control the dipole-dipole interactions in the molecules and prepared the first tetranuclear Tb(III) 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{7(2),8(2),12(2),13(2),17(2),18(2)-hexabutoxytribenzo[g,l,q]-5,10,15,20-tetraazaporphirino}[b,e]benzenato). In direct-current magnetic susceptibility measurements, ferromagnetic interactions among the four Tb(3+) 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 Tb(III)Pc 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 Tb(3+) 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 Tb(III) SMMs. Our work shows that the SMM properties can be fine-tuned by introducing weak intermolecular magnetic interactions in a controlled SMM spatial arrangement.
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