Coordination Programming: Science of Molecular Superstructures for Chemical Devices

東北大学 / 金沢大学金属材料研究所D/A集積体を基にした磁性・伝導性・誘電応答の“外部摂動”制御に関する研究について、以下の課題iii)ーv)について検討した。課題iii）二次元層状化合物[{Ru2(CF3CO2)4}2(TCNQ)]・2(anthracene)・n(solvent)の脱溶媒による格子内アントラセン分子異動のダイナミクスに関する研究を展開した。この化合物は、溶媒が脱離することで、結晶ー結晶転移を起こし、脱溶媒化合物に変化する。その時、層間に挟まれたアントラセン分子は、脱離した溶媒のスペースを埋めるように、約４０％の分子が結晶内を移動する。この移動ダイナミクスを粉末X線回折で捉える実験を行った。また、二次元層状化合物の他に、アントラセンが挿入されたラダー型の化合物を作ることにも成功し、その溶媒脱離に関する研究も行った。多孔性配位高分子が注目を集めているが、自然界は真空空孔を嫌う。そのため、もし結晶内に移動可能な分子があった場合、細孔を埋めるように安定化を図るのかもしれない。このような系は非常に珍しく、極めて重要な知見を与える。課題iv）本系で扱うD/A系の幾つかは、高電場をかけることにより非線形伝導を示す。この非線形伝導状態の外部磁場依存性について検討を行った。課題v）本系で扱う化合物は、溶媒脱離などにより構造を保持したまま結晶ー結晶転移を起こすが、同時に、生じた結晶中のスペースを利用した置換基のフリップ運動が見られる場合がある。特にこのような系について、溶媒和状態（OFF）と脱溶媒状態（ON）で置換基のフリップ運動から誘起される電場応答について測定を開始した。外場として溶媒脱着や選択的な分子（ガス分子など）の吸脱着を利用して、その効果を電気信号でアウトプットする系は、今後多孔性分子材料の研究では極めて重要になってくる。分子の吸脱着を直接観測するのはなく、微小系利用による、高感度、即応的な電気信号をどのように得るべきかが今後の課題である。研究課題/領域番号:24108714, 研究期間(年度):2012-04-01 – 2014-03-3

Effect of pressure on single-chain magnets with repeating units of the MnIII-NiII-MnIII trimer

The single-chain magnet (SCM) system [Mn2(saltmen)2Ni(pao)2(L)2](A)2 (L: intrachain attaching ligand of NiII ion; A-1: interchain counteranion) is a ferromagnetic one-dimensional network system with repeating units of the MnIII-NiII-MnIII trimer which itself behaves as a single-molecule magnet with an S=3 spin ground state and negative uniaxial single-ion anisotropy (D) parallel to the bridging direction. The slow relaxation of the magnetic moment in this SCM system originates in an energy barrier for spin reversal (ΔE), which is closely related to the ferromagnetic interaction between the trimers (Jtrimer) as well as to the D of the trimer. We have investigated the effects of pressure on three compounds representative of the above SCM family through ac susceptibility measurements under hydrostatic pressures up to P=13.5 kbar and crystal structural analysis experiments up to P=20.0 kbar, and have observed a pronounced enlargement of ΔE when J was artificially increased. The application of hydrostatic pressure brought about the systematic enhancement of EΔ (a maximum increase of 10% within the pressure region of the experiments). The pressure dependence of EΔ varied according to the kind of attaching ligand L involved and the intrachain structure, and we have experimentally found that isotropic lattice shrinkage is desirable if a continuous increase of ΔE in this system is aimed at

Life and How to Live It

The reaction of Mn^III salen-type complexes with di- and tetraanionic α-Keggin-type polyoxometalates (POMs) was performed, and three types of Coulombic aggregations containing Mn^III out-of-plane dimeric units (abbreviated as [Mn₂]²⁺) that are potentially single-molecule magnets (SMMs) with an <i>S</i>_T = 4 ground state were synthesized: [Mn₂(5-MeOsaltmen)₂(acetone)₂]­[SW₁₂O₄₀] (<b>1</b>), [Mn₂(salen)₂(H₂O)₂]₂[SiW₁₂O₄₀] (<b>2</b>), and [Mn­(5-Brsaltmen)­(H₂O)­(acetone)]₂[{Mn₂(5-Brsaltmen)₂}­(SiW₁₂O₄₀)] (<b>3</b>), where 5-Rsaltmen^2– = <i>N</i>,<i>N</i>′-(1,1,2,2-tetramethylethylene)­bis­(5-R-salicylideneiminate) with R = MeO (methoxy), Br (bromo) and salen^2– = <i>N</i>,<i>N</i>′-ethylenebis­(salicylideneiminate). Compound <b>1</b> with a dianionic POM, [SW₁₂O₄₀]^2–, is composed of a 1:1 aggregating set of [Mn₂]²⁺/POM, and <b>2</b>, with a tetraanionic POM, [SiW₁₂O₄₀]^4–, is a 2:1 set. Compound <b>3</b> with [SiW₁₂O₄₀]^4– forms a unique 1D coordinating chain with a [−{Mn₂}–POM−]^2– repeating unit, for which a hydrogen-bonded dimeric unit ([Mn­(5-Brsaltmen)­(H₂O)­(acetone)]₂²⁺) is present as a countercation. Independent of the formula ratio of [Mn₂]²⁺/POM, Mn^III dimers and POM units in <b>1</b>–<b>3</b> form respective segregated columns along a direction of the unit cell, which make an alternate packing to separate evenly identical species in a crystal. The nearest intermolecular Mn···Mn distance is found in the order <b>2</b> < <b>3</b> < <b>1</b>. The segregation of the [Mn₂]²⁺ dimer resulted in interdimer distances long enough to effectively reduce the intermolecular magnetic interaction, in particular in <b>1</b> and <b>3</b>. Consequently, an intrinsic property, SMM behavior, of Mn^III dimers has been characterized in this system, even though the interdimer interactions are still crucial in the case of <b>2</b>, where a long-range magnetic order competitively affects slow relaxation of the magnetization at low ac frequencies

Glauber dynamics in a single-chain magnet: From theory to real systems

The Glauber dynamics is studied in a single-chain magnet. As predicted, a single relaxation mode of the magnetization is found. Above 2.7 K, the thermally activated relaxation time is mainly governed by the effect of magnetic correlations and the energy barrier experienced by each magnetic unit. This result is in perfect agreement with independent thermodynamical measurements. Below 2.7 K, a crossover towards a relaxation regime is observed that is interpreted as the manifestation of finite-size effects. The temperature dependences of the relaxation time and of the magnetic susceptibility reveal the importance of the boundary conditions.Comment: Submitted to PRL 10 May 2003. Submitted to PRB 12 December 2003; published 15 April 200

Spin correlation and relaxational dynamics in molecular-based single-chain magnets

We report the combined measurements of the dc susceptibility X0, the ac susceptibility X, and the NMR relaxation rate T for the molecular-based heterometallic single-chain magnet [Mn(saltmen)]2[Ni(pao)2(py)2](PF6)2. At low temperatures, this system is well described by a one-dimensional array of effective spin S=3 chains comprising the MnIII-NiII-MnIII trimers and treated as the S=3 Ising chain with the single-ion term (Blume-Capel model). Using the exact solution of the model and based on the picture that the random motion of the local domain walls dominates the low-temperature spin dynamics, we succeeded in reproducing the experimental results of the dc susceptibility X0, the ac susceptibility X, and the 19F-NMR relaxation rate T in a consistent manner