Symmetry of octa-coordination environment has a substantial influence on dinuclear TbIII triple-decker single-molecule magnets

Abstract

Single-molecule magnet (SMM) properties of terbium(III)-phthalocyaninato and porphyrinato mixed ligand triple-decker complexes, [(TTP)Tb(Pc)Tb(TTP)] (1) and [(Pc)Tb(Pc)Tb(TTP)] type (2), were studied and were compared with those of the Tb^III homoleptic triple-decker complex [(obPc)Tb(obPc)Tb(obPc)] (3) in order to elucidate the relationship between octa-coordination environments and SMM properties (Tb^III = terbium(III), TTP²⁻ = tetraphenylporphyrinato, Pc²⁻ = phthalocyaninato, obPc²⁻ = 2,3,9,10,16,17,23,24-octabutoxyphthalocyaninato). By combining TTP²⁻ and Pc²⁻ with Tb^III ions, it is possible to make three octa-coordination environments: SP–SP, SAP–SP and SAP–SAP sites, where SAP is square-antiprismatic and SP is square-prismatic. The direction and magnitude of the ligand field (LF) strongly affect the magnetic properties. Complexes 2 and 3, which have SAP–SAP sites, undergo dual magnetic relaxation processes in the low temperature region in a direct current magnetic field. On the other hand, 1, which has an SP–SP environment, undergoes a single magnetic relaxation process, indicating that the octa-coordination environments strongly influence the SMM properties. The SMM behaviour of dinuclear Tb^III SMMs 1–3 were explained by using X-ray crystallography and static and dynamic susceptibility measurements. This work shows that the SMM properties can be fine-tuned by introducing different octa-coordination geometries with the same Tb^III–Tb^III distances.