76 Chemical Science In principle, a single spin can be used as a ‘bit’ of information to prepare high-density storage and quantum computing devices [1]. Quantum tunneling of the magnetization (QTM) between double well potentials, which is a prominent, characteristic property of single molecule magnets (SMMs), underpins this concept. SMMs behave like magnets with frozen spins, and a potential exists across two energy barriers at low temperatures, known as the blocking temperature ( T B ). In the case of 3 d cluster SMMs, an easy axis- type magnetic anisotropy, which is represented by a negative zero-field splitting constant ( D ), occurs due to magnetic interactions among high-spin 3 d metal ions in the clusters. Researchers have been studying complexes with higher values of T B than that of a well- known Mn cluster. In recent years, lanthanoid(III)- phthalocyaninato (Ln(III)-Pc) sandwich complexes have been shown to be SMMs, which originates from the ligand field (LF), and researchers have utilized their QTM and magnetic relaxation behavior [2]. Ln(III)-Pc molecules showing SMM behavior have significantly large axial magnetic anisotropies, which occur by a different mechanism than those for known 3 d metal cluster SMMs. On the other hand, in the case of Ln(III) SMMs, the LF of the Ln 3+ ion controls the anisotropy. The LF potential around a Tb 3+ ion (4 f 8 ) with a total angular momentum ( J ) of 6 splits the ground multiplet so that the lowest sublevel has the largest J z value ( | J z | = 6, corresponding to up/down spin states) and large energy gaps to the remaining sublevels. Being able to control the QTM of Ln(III)-Pc SMMs will make it possible to design new spintronics devices. In this study, we report the molecular structure and magnetic relaxation properties of dinuclear Ln(III)- Pc multiple-decker complexes: quadruple-decker {[Ln(obPc) 2 ]Cd[Ln(obPc) 2 ]} ( 1 : Ln = Tb 3+ , 2 : Ln = Dy 3+ ), triple-decker Ln 2 (obPc) 3 ( 3 : Ln = Tb 3+ , 4 : Ln = Dy 3+ ), double-decker Ln(obPc) 2 ( 5 : Ln = Tb 3+ , 6 : Ln = Dy 3+ ), and quintuple-decker {[Tb(obPc) 2 ]Cd(obPc) Cd[Tb(obPc) 2 ]} ( 7 ). Our work shows that the SMM/ QTM properties can be fine-tuned by introducing weak intermolecular magnetic interactions in controlled spatial arrangements of lanthanides ions [3]. In order to control the spin orientation in the molecules, we designed 1–7 so that the two Ln 3+ ions are along the anisotropy axis ( Fig. 1). The SMM behavior of dinuclear Ln(III)-Pc multiple-decker complexes (Ln = Tb 3+ and Dy 3+ ) with large energy barriers and slow-relaxation behavior were explained by using X-ray crystallography (Figs. 2(a) and 2(b): BL02B1 and BL40XU beamlines) and static and dynamic susceptibility measurements [3]. There was a decrease in the in-phase ( χ M ') and out-of-phase ( χ M ") peaks in different T ranges, which were dependent on the frequency ( f ), indicating that dinuclear Ln(III)- Pc multiple-decker complexes (Ln = Tb 3+ and Dy 3+ ) are SMMs. In micro-SQUID experiments, quadruple- decker 1 and 2 clearly exhibited SMM behavior ( Fig. 2(c)) [3]. Dinuclear Tb(III)-Pc multiple-decker SMMs 1 , 3 , and 7 exhibited dual magnetic relaxation processes ( Fig. 3) [3]. These magnetic relaxation processes have T - independent ( τ 1 ) and T - dependent ( τ 2 ) regimes in the low T region. The dual magnetic relaxation behavior was observed not only for discreet dinuclear Tb(III)-Pc complexes but also for the spatially closed Tb(III)-Pc double-decker complex 5 [4]. On the other hand, mononuclear system 5a , where the effects of intermolecular interactions in 5 have been eliminated, exhibited only a single magnetic relaxation process [4]. In the case of the dinuclear Tb(III)-Pc complexes, the value of T B and the distance between Tb 3+ ions follows the strength of the dipole-dipole interactions ( D ij ), and T B shifted to the high- T side, indicating that the Tb 3+ – Tb 3+ interactions affect the spin dynamics ( Fig. 2(d)). Moreover, the presence of the dual magnetic relaxation processes is related to the distance between Tb 3+ ions sites in the dinuclear complexes ( Fig. 3). I n o t h e r w o r d s , t h e m a g n e t i c r e l a x a t i o n mechanism depends heavily on the dipole-dipole ( f-f ) interactions between the Tb 3+ ions in the dinuclear systems [3]. The above results demonstrate that even weak exchange interactions can have a large influence on the quantum properties of Ln(III)-Pc type SMMs. Two magnetic relaxation processes occur under the Multiple-decker phthalocyaninato dinuclear terbium (III) single-molecule magnets with dual-magnetic relaxation processes Ln = Tb 3+ , Dy 3+ obPc 5a :double-decker 3 :triple-decker 1 :quadruple-decker 7 :quintuple-decker Cd 2+ Cd 2+ Cd 2+ Ln 3+ obPc = 2,3,9,10,16,17,23,24- octabutoxyphthalocyaninato N N N N N N – N – O O O O O O O O N Fig. 1. Schematic illustration of sequential synthetic routes for multiple-decker phthalocyaninato dinuclear lanthanoid (III) single-molecule magnets [3]. 76 Chemical Science In principle, a single spin can be used as a ‘bit’ of information to prepare high-density storage and quantum computing devices [1]. Quantum tunneling of the magnetization (QTM) between double well potentials, which is a prominent, characteristic property of single molecule magnets (SMMs), underpins this concept. SMMs behave like magnets with frozen spins, and a potential exists across two energy barriers at low temperatures, known as the blocking temperature ( T B ). In the case of 3 d cluster SMMs, an easy axis- type magnetic anisotropy, which is represented by a negative zero-field splitting constant ( D ), occurs due to magnetic interactions among high-spin 3 d metal ions in the clusters. Researchers have been studying complexes with higher values of T B than that of a well- known Mn cluster. In recent years, lanthanoid(III)- phthalocyaninato (Ln(III)-Pc) sandwich complexes have been shown to be SMMs, which originates from the ligand field (LF), and researchers have utilized their QTM and magnetic relaxation behavior [2]. Ln(III)-Pc molecules showing SMM behavior have significantly large axial magnetic anisotropies, which occur by a different mechanism than those for known 3 d metal cluster SMMs. On the other hand, in the case of Ln(III) SMMs, the LF of the Ln 3+ ion controls the anisotropy. The LF potential around a Tb 3+ ion (4 f 8 ) with a total angular momentum ( J ) of 6 splits the ground multiplet so that the lowest sublevel has the largest J z value ( | J z | = 6, corresponding to up/down spin states) and large energy gaps to the remaining sublevels. Being able to control the QTM of Ln(III)-Pc SMMs will make it possible to design new spintronics devices. In this study, we report the molecular structure and magnetic relaxation properties of dinuclear Ln(III)- Pc multiple-decker complexes: quadruple-decker {[Ln(obPc) 2 ]Cd[Ln(obPc) 2 ]} ( 1 : Ln = Tb 3+ , 2 : Ln = Dy 3+ ), triple-decker Ln 2 (obPc) 3 ( 3 : Ln = Tb 3+ , 4 : Ln = Dy 3+ ), double-decker Ln(obPc) 2 ( 5 : Ln = Tb 3+ , 6 : Ln = Dy 3+ ), and quintuple-decker {[Tb(obPc) 2 ]Cd(obPc) Cd[Tb(obPc) 2 ]} ( 7 ). Our work shows that the SMM/ QTM properties can be fine-tuned by introducing weak intermolecular magnetic interactions in controlled spatial arrangements of lanthanides ions [3]. In order to control the spin orientation in the molecules, we designed 1–7 so that the two Ln 3+ ions are along the anisotropy axis ( Fig. 1). The SMM behavior of dinuclear Ln(III)-Pc multiple-decker complexes (Ln = Tb 3+ and Dy 3+ ) with large energy barriers and slow-relaxation behavior were explained by using X-ray crystallography (Figs. 2(a) and 2(b): BL02B1 and BL40XU beamlines) and static and dynamic susceptibility measurements [3]. There was a decrease in the in-phase ( χ M ') and out-of-phase ( χ M ") peaks in different T ranges, which were dependent on the frequency ( f ), indicating that dinuclear Ln(III)- Pc multiple-decker complexes (Ln = Tb 3+ and Dy 3+ ) are SMMs. In micro-SQUID experiments, quadruple- decker 1 and 2 clearly exhibited SMM behavior ( Fig. 2(c)) [3]. Dinuclear Tb(III)-Pc multiple-decker SMMs 1 , 3 , and 7 exhibited dual magnetic relaxation processes ( Fig. 3) [3]. These magnetic relaxation processes have T - independent ( τ 1 ) and T - dependent ( τ 2 ) regimes in the low T region. The dual magnetic relaxation behavior was observed not only for discreet dinuclear Tb(III)-Pc complexes but also for the spatially closed Tb(III)-Pc double-decker complex 5 [4]. On the other hand, mononuclear system 5a , where the effects of intermolecular interactions in 5 have been eliminated, exhibited only a single magnetic relaxation process [4]. In the case of the dinuclear Tb(III)-Pc complexes, the value of T B and the distance between Tb 3+ ions follows the strength of the dipole-dipole interactions ( D ij ), and T B shifted to the high- T side, indicating that the Tb 3+ – Tb 3+ interactions affect the spin dynamics ( Fig. 2(d)). Moreover, the presence of the dual magnetic relaxation processes is related to the distance between Tb 3+ ions sites in the dinuclear complexes ( Fig. 3). I n o t h e r w o r d s , t h e m a g n e t i c r e l a x a t i o n mechanism depends heavily on the dipole-dipole ( f-f ) interactions between the Tb 3+ ions in the dinuclear systems [3]. The above results demonstrate that even weak exchange interactions can have a large influence on the quantum properties of Ln(III)-Pc type SMMs. Two magnetic relaxation processes occur under the Multiple-decker phthalocyaninato dinuclear terbium (III) single-molecule magnets with dual-magnetic relaxation processes Ln = Tb 3+ , Dy 3+ obPc 5a :double-decker 3 :triple-decker 1 :quadruple-decker 7 :quintuple-decker Cd 2+ Cd 2+ Cd 2+ Ln 3+ obPc = 2,3,9,10,16,17,23,24- octabutoxyphthalocyaninato N N N N N N – N – O O O O O O O O N Fig. 1. Schematic illustration of sequential synthetic routes for multiple-decker phthalocyaninato dinuclear lanthanoid (III) single-molecule magnets [3].
home
- JP
- EN