Motohiro Nakano

Cobalt single-molecule magnet

A cobalt molecule that functions as a single-molecule magnet, [Co4(hmp)4(MeOH)4Cl4], where hmp− is the anion of hydroxymethylpyridine, is reported. The core of the molecule consists of four Co(II) cations and four hmp− oxygen atom ions at the corners of a cube. Variable-field and variable-temperature magnetization data have been analyzed to establish that the molecule has a S=6 ground state with considerable negative magnetoanisotropy. Single-ion zero-field interactions (DSz2) at each cobalt ion are the origin of the negative magnetoanisotropy. A single crystal of the compound was studied by means of a micro-superconducting quantum interference device magnetometer in the range of 0.040–1.0 K. Hysteresis was found in the magnetization versus magnetic field response of this single crystal.

Wheel-Shaped ErIIIZnII3Single-Molecule Magnet: A Macrocyclic Approach to Designing Magnetic Anisotropy

Single-molecule magnets (SMMs) are chemically and physically interesting compounds that exhibit hitherto unobserved magnetic properties. To prevent reversal of the molecular magnetic moment, the use of heavy lanthanide ions is becoming popular because of their large spin multiplicity and large magnetic anisotropies in the ground state. Lanthanide ions exhibit flexibility in magnetic anisotropy, which is another advantage of Ln-based SMMs that is attributable to the flexible design and control of the ligandfield (LF) anisotropy. These anisotropies are correlated through Stevens factor qm as B n m 1⁄4 Am r h iqm, where Bm denotes the mth-order magnetic anisotropy parameters (m is 2, 4, or 6 for lanthanide ions; n varies between 0 and m ; second-order terms of B2 and B 2 2 correspond to the axial and rhombic anisotropic parameters D and E), and Am r m h i denotes the LF anisotropy parameters. Therefore, Ln complexes have a wide scope in the synthetic design of anisotropic magnets. Although many complexes including one or more heavy lanthanide ions are reported to be SMMs, most of them were synthesized in a fortuitous manner without design of the magnetic anisotropy. We have demonstrated previously that an axial LF, whereby donor atoms with higher negative charges are located along the principal axis, induces a strong Ising-type anisotropy of Tb and Dy ions. This type of LF anisotropy is easily achieved in an accidental manner, and thus a wide variety of Tb and Dy SMMs have been reported. On the contrary, Er-based SMMs are rare. When the second-order anisotropy terms are dominant, magnetic anisotropy of the Er ion has opposite features to those of Tb and Dy ions, since the q2 parameter of the Er III

Structural Design of Easy-Axis Magnetic Anisotropy and Determination of Anisotropic Parameters of LnIIICuII Single-Molecule Magnets

Four dinuclear Ln(III)-Cu(II) complexes with Ln=Tb (1), Dy (2), Ho (3), and Er (4) were synthesized to investigate the relationship between their respective magnetic anisotropies and ligand-field geometries. These complexes were crystallographically isostructural, and a uni-axial ligand field was achieved by using three phenoxo oxygen groups. Complexes 1 and 2 displayed typical single-molecule magnet (SMM) behaviors, of which the out-of-phase susceptibilities were observed in the temperature range of 1.8-5.0 K (1) and 1.8-20.0 K (2). The Cole-Cole plots exhibited a semicircular shape with α parameters in the range of 0.08-0.18 (2.6-4.0 K) and 0.07-0.24 (3.5-7.0 K). The energy barriers Δ/k(B) were estimated from the Arrhenius plots to be 32.9(4) K for 1 and 26.0(5) K for 2. Complex 3 displayed a slow magnetic relaxation below 3.0 K, whereas complex 4 did not show any frequency-dependent behavior for both in-phase and out-of-phase susceptibilities, which indicates that easy-axis anisotropy was absent. The temperature dependence of the dc susceptibilities for the field-aligned samples of 1-3 revealed that the χ(M) T value continuously increased as the temperature was lowered, which indicates the presence of low-lying Stark sublevels with the highest |J(z) | values. In contrast, complex 4 displayed a smaller and temperature-independent χ(M) T value, which also indicates that easy-axis anisotropy was absent. Simultaneous analyses were carried out for 1-3 to determine the magnetic anisotropy parameters on the basis of the Hamiltonian that considers B(2) (0) , B(4) (0) , and B(6) (0) .

Coordination-Tuned Single-Molecule-Magnet Behavior of TbIII-CuII Dinuclear Systems

Tb (III)-Cu (II)-based single-molecule magnet (SMM) and non-SMM were synthesized to investigate the relationship between magnetic anisotropy and the symmetry of the ligand field by the reaction of [TbCu( o-vanilate) 2(NO 3) 3] with methoxypropylamine (MeOC 3H 6NH 2, 1) or ethoxyethylamine (EtOC 2H 4NH 2, 2). In both complexes, Tb (III) ions have a bicapped square-antiprism coordination geometry. When the Tb (III) ion is in a less symmetrical ligand field, it has an easy-axis anisotropy and shows SMM behavior, whereas when it is in a more symmetrical environment, it has an easy-plane anisotropy and exhibits non-SMM behavior.

Magnetic Relaxation of Single‐Molecule Magnets in an External Magnetic Field: An Ising Dimer of a Terbium(III)–Phthalocyaninate Triple‐Decker Complex

The idea of using a single spin as a “bit” of information to prepare high-density storage and quantum-computing deACHTUNGTRENNUNGvices has caused an increase in scientific and technological interests. Quantum tunneling of the magnetization (QTM) in double-well potentials, which is a characteristic property of single-molecule magnets (SMMs), is the underlying phenomenon for this idea. On the basis of the properties of lanthanoid–phthalocyaninate ([LnPc2]) SMMs, [4] we believe that [TbPc2] can be used as a “bit” of information in highdensity storage technology by taking advantage of the single up-spin/down-spin property, which is equivalent to 2. The up-spin/down-spin properties of tripleand quadrupledecker-type SMMs are equivalent to 2 and 2, respectively, in relation to the number of spins. We have recently reported the characteristics of [MPc2] and [MPc] (M= Tb, Dy, and Y) deposited on an AuACHTUNGTRENNUNG(111) surface in an ultrahigh vacuum (UHV) using a dry process technique. Both [MPc2] and [MPc] are present on the AuACHTUNGTRENNUNG(111) surface on the basis of height profiles and dI/dV mapping obtained by using scanning tunneling microscopy (STM) and spectroscopy (STS). A Kondo peak, which is due to coupling between magnetic impurities, including Tb ions, and conduction electrons from the STS, is only observed at the center of [TbPc] at a Kondo temperature (TK) of 250 K. More recently, we have observed a Kondo peak for [TbPc2] on an AuACHTUNGTRENNUNG(111) surface. Therefore, the relation between TK and the blocking temperature (TB) must be discussed further. In addition, the properties of SMMs and the Kondo effect can be modulated with an external magnetic field. Here we present the results of studies on the SMM properties of a new Tb triple-decker phthalocyaninate derivative, [Tb2ACHTUNGTRENNUNG(obPc)3] (1; obPc =dianion of 2,3,9,10,16,17,23,24octabutoxyphthalocyanine). The relationships among the molecular structure, ligand-field, ground-state, and SMM properties in a direct current (dc) magnetic field are discussed. It is important to both understand and control the quantum properties of SMMs with an external field. The triple-decker complex 1 is composed of three Pc ligACHTUNGTRENNUNGands and two Tb ions, resulting in a neutral complex with a closed shell p electron system. We used a Pc ligand with 2,3,9,10,16,17,23,24-octabutoxy substituents because it should have a higher solubility and crystallization should be easier. Complex 1 was synthesized in one step starting from [Tb ACHTUNGTRENNUNG(acac)3]·4H2O and H2obPc, following a published procedure (see Experimental Section). This complex is soluble in most organic solvents, except for alcohols. Complex 1 crystallized with ethanol in the crystal lattice in the triclinic space group P1̄, as shown in Figure 1. The crystal data are summarized in Table S1 and crystal-packing [a] Dr. K. Katoh, Prof. B. K. Breedlove, Prof. M. Yamashita Department of Chemistry, Graduate School of Science Tohoku University, 6–3 Aramaki-Aza-Aoba, Aoba-ku Sendai, Miyagi 980-8578 (Japan) Fax: (+81) 22-795-6548 E-mail : kkatoh@m.tains.tohoku.ac.jp yamasita@agnus.chem.tohoku.ac.jp [b] Prof. T. Kajiwara Department of Chemistry, Faculty of Science Nara Women s University, Nishi-Machi Kita-Uoya, Nara 565-0871 (Japan) [c] Prof. M. Nakano Department of Applied Chemistry Graduate School of Engineering, 2–1 Yamadaoka Suita, Osaka 565-0871 (Japan) [d] Prof. Y. Nakazawa, Prof. N. Ishikawa Department of Chemistry, Graduate School of Science 1-1 Machikaneyama-Cho, Toyonaka Osaka 560-0043 (Japan) [e] Prof. W. Wernsdorfer Laboratory Louis N el, CNRS, BP 166, 38042 Grenoble Cedex 9 (France) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201002026.

Crystal design of monometallic single-molecule magnets consisting of cobalt-aminoxyl heterospins

Five N-aryl-N-pyridylaminoxyls, which have no substituent (PhNOpy), one substituent (MeOPhNOpy and tert-BuPhNOpy) at the 4-position, and three substituents (TPPNOpy and TBPNOpy) at the 2, 4, and 6-positions of the phenyl ring, were prepared as new ligands for cobalt-aminoxyl heterospin systems. The 1:4 complexes, [Co(NCS)2(PhNOpy)4] (1), [Co(NCS)2(MeOPhNOpy)4] (2), [Co(NCS)2(tertBuPhNOpy)4] (3), [Co(NCS)2(TPPNOpy)4] (4), [Co(NCS)2(TBPNOpy)4] (5a), and [Co(NCO)2(TBPNOpy)4] (5b), were obtained as single crystals. The molecular geometry revealed by X-ray crystallography for all complexes except 4 is a compressed octahedron. In the crystal structure of 1, 2, and 3, the organic spin centers have various short contacts within 4 A with the neighboring molecules to form 3D and 2D spin networks. On the other hand, complexes 5a and 5b have no significant short intermolecular contacts, indicating that they are magnetically isolated. 1 and 2 behaved as a 3D antiferromagnet with a Neel temperature, T(N), of 22 K and as a weak 3D antiferromagnet with a T(N) of 2.9 K and a spin-flop field at 1.9 K, Hsp(1.9), of 0.7 kOe, respectively. 3 was a canted 2D antiferromagnet (a weak ferromagnet) with T(N) = 4.8 K and showed a hysteresis loop with a coercive force, Hc, of 1.3 kOe at 1.9 K. On the other hand, the trisubstituted complexes 4, 5a, and 5b functioned as single-molecule magnets (SMMs). 5b had an effective activation barrier, U(eff), value of 28 K in a microcrystalline state and 48 K in a frozen solution.

Update 1 of: calorimetric investigation of phase transitions occurring in molecule-based magnets.

Occurring in Molecule-Based Magnets† Michio Sorai,*,‡ Yasuhiro Nakazawa,‡,§ Motohiro Nakano, and Yuji Miyazaki‡ ‡Research Center for Structural Thermodynamics, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan Department of Applied Chemistry, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan

Observation of nanostructure by scanning near-field optical microscope with small sphere probe

Abstract Step and terrace structure has been observed in an area of 1 μm × 1 μm on the cleaved surface of KCl–KBr solid-solution single crystal by scanning near-field optical microscope (SNOM) with a small sphere probe of 500 nm diameter. Lateral spatial resolution of the SNOM system was estimated to be 20 nm from the observation of step width and the scanning-step interval. Vertical spatial resolution was estimated to be 5–2 nm from the observation of step height and noise level of photomultiplier tube (PMT). With applying a dielectric dipole radiation model to the probe surface, the reason why such a high spatial resolution was obtained in spite of the 500 nm sphere probe, was understood as the effect of the near-field term appeared in the radiation field equations.

A manganese single-chain magnet exhibits a large magnetic coercivity

A manganese single-chain magnet, [Mn(6)O(2)(4-MeOsalox)(6)(N(3))(2)(MeOH)(4)](n) (4-MeO-H(2)salox = 2-hydroxy-4-methoxybenzaldehyde oxime), is synthesized via the assembly of Mn(6) single-molecule magnets, which exhibits a large magnetic coercivity.

A ferromagnetically coupled Fe 42 cyanide-bridged nanocage

Self-assembly of artificial nanoscale units into superstructures is a prevalent topic in science. In biomimicry, scientists attempt to develop artificial self-assembled nanoarchitectures. However, despite extensive efforts, the preparation of nanoarchitectures with superior physical properties remains a challenge. For example, one of the major topics in the field of molecular magnetism is the development of high-spin (HS) molecules. Here, we report a cyanide-bridged magnetic nanocage composed of 18 HS iron(III) ions and 24 low-spin iron(II) ions. The magnetic iron(III) centres are ferromagnetically coupled, yielding the highest ground-state spin number (S=45) of any molecule reported to date.