单分子磁体研究的最新进展

宏观上表现出可测的慢磁弛豫行为的单个分子称为单分子磁体,它主要包括过渡金属单分子磁体和稀土单分子磁体,其在量子计算、高密度信息存储以及自旋器件等方面的潜在应用吸引了研究者的广泛关注.本文介绍了单分子磁体研究的最新进展,重点总结了构筑高性能单分子磁体的合成策略.     

3d-4f单分子磁体*

单分子磁体是指那些在磁场下能够被磁化,当磁场去除后仍能保持磁性的单个分子。由于在信息处理和储存方面具有潜在的广泛应用前景,单分子磁体日益成为化学、材料科学和物理等学科的研究热点。近年来,同时含有镧系金属离子和过渡金属离子的3d-4f单分子磁体更是引起了很多研究者的兴趣。本文阐述了3d-4f单分子磁体的优势,总结了3d-4f单分子磁体的常见合成方法及其磁性,分析了影响3d-4f单分子磁体磁性的因素。     

稀土单分子磁体的研究进展

在信息存储和量子计算方面具有广阔应用前景的单分子磁体及相关研究中,应用各向异性显著的稀土离子以期提高单分子磁体自旋翻转能垒的研究倍受关注。 本文综述了稀土单分子磁体的研究进展,并着重介绍了单核、三核及四核镝配合物单分子磁体的磁学性质。     

单分子磁体及其磁学表征*

单分子磁体是介于分子基磁体和纳米磁性材料的学科交叉点.对其不同寻常磁特性的研究不仅有助于纳米磁性离子物理学和化学的发展,而且有望最终用于高密度信息储存设备.本文就单分子磁体的研究背景和意义、单分子磁体的种类、结构及磁学表征作一概述.     

锕系单分子磁体研究进展

单分子磁体是一类由单个分子组成的磁性材料,其磁性起源于单个分子的磁矩,有望在超高密度存储、量子计算机、自旋电子学等领域得到应用.由于锕系元素极大的旋轨耦合效应及5f轨道的延展性,锕系单分子磁体越来越受到人们的关注,期待未来磁学性能甚至能超越过渡及镧系金属.然而,目前对于锕系单分子磁体的弛豫机理及慢磁行为的影响因素仍尚未明确.本综述总结了近10多年以来报道的锕系单分子磁体,发现有效能垒的实验值和理论值极不相符,一定程度限制了锕系单分子磁体的发展.最后,对未来的锕系单分子磁体研究方向进行了展望.     

3d过渡金属单离子磁体

单分子磁体在量子计算、高密度存储材料以及分子自旋电子学等领域具有广阔的应用前景。3d过渡金属单离子磁体具有结构简单、易于研究磁构关系以及可控配体场获得高能垒等特点,因而成为近年来单分子磁体领域的研究热点。本文结合现有研究成果,从配位构型出发,旨在对近年来基于3d过渡金属离子的单离子磁体进行综述,重点阐述配体场、磁各向异性和单离子磁体性质三者之间的关系,为设计合成单分子磁体提供新的思路。     

多酸构筑的单分子磁体

设计合成具有单分子磁体行为的分子磁性材料近年来受到广泛关注. 合成单分子磁体的一个常用策略是利用有机多齿含氧或含氮配体将各种自旋载体组装成簇,使之具有高基态自旋值(S)和负的单轴磁各向异性值(D),进而满足形成单分子磁体所需的磁能垒. 令人感兴趣的是近年来多酸发展成为一类构筑新型单分子磁体的无机建筑基元. 多酸是一类独特的具有富氧表面、可控的尺寸、形状和电荷的无机纳米级金属氧簇,同时,一系列缺位多酸衍生物能够结合各种过渡金属或稀土离子形成多核金属簇合物. 近五年来,多酸已作为一类无机多齿含氧配体成功构筑系列具有单分子磁体行为的新型过渡金属簇合物、稀土簇合物和3d-4f杂金属簇合物. 特别是一些缺位多酸配体能够为稀土离子提供完美的配体场,进而构筑新一代的单离子磁体. 此外,高自旋、磁各向异性单元(如单分子磁体)还可被均匀分散在具有孔道特征的多酸三级结构中,形成具有单分子磁体行为的多酸基复合材料. 最近,以多酸为模板构筑具有单分子磁体行为的多核簇合物也取得了新进展. 本综述旨在对近五年来利用多酸构筑的单分子磁体化合物进行评论,重点阐述利用多酸设计合成单分子磁体的策略、多酸在单分子磁体化合物结构中的作用和优势,以及多酸构筑单分子磁体这一研究课题的发展前景.     

稀土单分子磁体

单分子磁体因其磁性双稳态和慢弛豫机制而在超高密度存储材料、自旋电子器件等领域具有潜在的应用. 稀土单分子磁体因为具有较大的磁矩和磁各向异性而成为近年来研究的热点话题. 目前有关稀土单分子磁体的综述都主要集中在它们的合成、结构及磁性能, 而在其它性质方面缺少深入而系统的研究. 因此, 本论文结合现有的研究成果, 围绕稀土单分子磁体的高翻转能垒、复杂的多弛豫机制、可调控的磁性以及多功能材料的四个特点进行了综述, 旨在更好的理解稀土单分子磁体的物理、化学本质, 为稀土单分子磁体的设计与调控提供思路.     

单离子磁体及其磁弛豫动力学的研究进展

单分子磁体因其在高密度信息存储、自旋电子学以及量子计算方面有潜在的应用价值而被广泛关注。单离子磁体是具有单个金属自旋中心的单分子磁体,其特点是结构简单、可设计性强和磁构关系更易研究。本文介绍了近年来典型的单离子磁体及其磁弛豫动力学的研究进展。     

稀土单分子磁体研究进展

单分子磁体是一类纳米尺度的磁性材料,在高密度信息存储、量子比特和自旋电子器件等方面具有潜在的应用价值而备受关注。由于稀土离子具有大的磁矩和强的磁各向异性,稀土离子在高性能单分子磁体构筑方面有过渡金属离子不可比拟的优势。近年来,以单核和双核稀土单分子磁体为代表的稀土单分子磁体的研究取得了长足的进展,尤其是突破了以液氮沸点温度(77 K)为界限的磁阻塞温度,为室温下的单分子信息存储迈出了坚实的一步。     

Single-Molecule Magnets: Different Rates of Resonant Magnetization Tunneling in Mn12 Complexes

Two new molecular magnets , the dodecanuclear manganese complexes of the type [Mn₁₂O₁₂(O₂CR)₁₆(H₂O)₄] (known for R = CH₃, new for R = o-ClC₆H₄, o-BrC₆H₄) have contributed to a better quantum mechanical understanding of single-molecule magnets. For instance, appreciable differences in the steps seen in the magnetization hysteresis loops of these high-spin clusters are attributed to changes in the rates of magnetization tunneling from one complex to another.     

Rational Design of a Lanthanide‐Based Complex Featuring Different Single‐Molecule Magnets

The rational synthesis of the 2‐{1‐methylpyridine‐N‐oxide‐4,5‐[4,5‐bis(propylthio)tetrathiafulvalenyl]‐1H‐benzimidazol‐2‐yl}pyridine ligand ( L ) is described. It led to the tetranuclear complex [Dy₄(tta)₁₂( L )₂] ( Dy‐Dy₂‐Dy ) after coordination reaction with the precursor Dy(tta)₃?2 H₂O (tta^?=2‐thenoyltrifluoroacetonate). The X‐ray structure of Dy‐Dy₂‐Dy can be described as two terminal mononuclear units bridged by a central antiferromagnetically coupled dinuclear complex. The terminal N₂O₆ and central O₈ environments are described as distorted square antiprisms. The ac magnetism measurements revealed a strong out‐of‐phase signal of the magnetic susceptibility with two distinct sets of data. The high‐ and low‐frequency components were attributed to the two terminal mononuclear single‐molecule magnets (SMMs) and the central dinuclear SMM, respectively. A magnetic hysteresis loop was detected at very low temperature. From both structural and magnetic points of view, the tetranuclear SMM Dy‐Dy₂‐Dy is a self‐assembly of two known mononuclear SMMs bridged by a known dinuclear SMM.     

Photo-responsive Single-Molecule Magnet Showing 0D to 1D Single-Crystal-to-Single-Crystal Structural Transition and Hysteresis Modulation

Photo-responsive lanthanide-based single-molecule magnets (SMM) hold great promise for future switching and memory devices. Herein, we report a dysprosium phosphonate [Dy^III(SCN)₂(NO₃)(depma)₂(4-hpy)₂] ( 1Dy ), which features a supramolecular framework containing layers of hydrogen-bonding network and pillars of π–π interacted anthracene units. The photocycloaddition reaction of anthracene pairs led to a rapid and reversible single-crystal-to-single-crystal (SC–SC) structural transition to form the 1D coordination polymer [Dy^III(SCN)₂(NO₃)(depma₂)(4-hpy)₂]_n ( 2Dy ), accompanied by photoswitchable SMM properties with the reduction of effective energy barrier by half and the narrowing of the butterfly-like hysteresis loop. The diluted sample showed a photo-induced switch of the blocking temperature (T_B) from 3.8 K for 1Dy@Y to 2.6 K for 2Dy@Y . This work may inspire the construction of lanthanide-based molecular materials with targeted photo-responsive magnetic properties.     

Langmuir–Blodgett Films of Single-Molecule Nanomagnets

Magnetic Langmuir–Blodgett films containing well-organized monolayers of single-molecule magnets are reported. The single-molecule magnets in question are high-spin molecular clusters of the type [Mn₁₂O₁₂(carboxylate)₁₆]. The structure of such multilayered inorganic–organic composites is depicted schematically in the figure.     

Breaking Symmetry Relaxes Structural and Magnetic Restraints,Suppressing QTM in Enantiopure Butterfly Fe2Dy2 SMMs**

The {Fe₂Dy₂} butterfly systems can show single molecule magnet (SMM) behaviour, the nature of which depends on details of the electronic structure, as previously demonstrated for the [Fe₂Dy₂(μ₃-OH)₂(Me-teaH)₂(O₂CPh)₆] compound, where the [N,N-bis-(2-hydroxyethyl)-amino]-2-propanol (Me-teaH₃) ligand is usually used in its racemic form. Here, we describe the consequences for the SMM properties by using enantiopure versions of this ligand and present the first homochiral 3d/4 f SMM, which could only be obtained for the S enantiomer of the ligand for [Fe₂Dy₂(μ₃-OH)₂(Me-teaH)₂(O₂CPh)₆] since the R enantiomer underwent significant racemisation. To investigate this further, we prepared the [Fe₂Dy₂(μ₃-OH)₂(Me-teaH)₂(O₂CPh)₄(NO₃)₂] version, which could be obtained as the RS-, R- and S-compounds. Remarkably, the enantiopure versions show enhanced slow relaxation of magnetisation. The use of the enantiomerically pure ligand suppresses QTM, leading to the conclusion that use of enantiopure ligands is a “gamechanger” by breaking the cluster symmetry and altering the intimate details of the coordination cluster's molecular structure.     

The Role of the −OH Groups within Mn12 Clusters in Electrocatalytic Water Oxidation

The formidable reactivity of the oxygen-evolving center near photosystem II is largely based on its protein environment that stabilizes it during catalysis. Inspired by this concept, the water-soluble Mn₁₂ clusters Mn₁₂O₁₂(O₂CC₆H₃(OH)₂)₁₆(H₂O)₄ (3,5DHMn₁₂) and Mn₁₂O₁₂(O₂CC₆H₃(OH)₃)₁₆(H₂O)₄ (3,4,5THMn₁₂) were developed as efficient electrocatalysts for water oxidation. In this work, the role of the −OH groups in the electrocatalytic process was explored by describing the structural and electrocatalytic properties of two new Mn₁₂ clusters, 3,4DHMn₁₂ and 2,3DHMn₁₂ , having one −OH group in the meta position relative to the benzoate-Mn moiety, and one at the para or ortho position, respectively. The Mn centers in 3,4DHMn₁₂ were discovered to have lower oxidation potential compared with those in 2,3DHMn₁₂ , and thus, 3,4DHMn₁₂ can catalyze water oxidation with higher rate and TON than 2,3DHMn₁₂ . Hence, the role of the −OH groups in the electrocatalysis was established, being involved in electronic stabilization of the Mn centers or in proton shuttling.     

Modelling the Magnetic Behaviour of Square‐Pyramidal CoII5 Aggregates: Tuning SMM Behaviour through Variations in the Ligand Shell

Three new μ₄‐bridged Co^II₅ clusters with similar core motifs have been synthesised with the use of N‐tert‐butyldiethanolamine (tbdeaH₂) and pivalic acid (piv): [Co^II₅(μ₄‐N₃)(tbdea)₂(μ‐piv)₄(piv)(CH₃CN)₂]?CH₃CN ( 1 ), [Co^II₅(μ₄‐Cl)(Cl)(tbdea)₂(μ‐piv)₄(pivH)₂] ( 2 ) and [Co^II₅(μ₄‐N₃)(Cl)(tbdea)₂(μ‐piv)₄(pivH)₂] ( 3 ). Magnetic measurements were performed for all three compounds. It was found that while the chloride‐bridged cluster 2 does not show an out‐of‐phase signal, which excludes single‐molecule magnet (SMM) behaviour, the azide‐bridged compounds 1 and 3 show out‐of‐phase signals as well as frequency dependence of the ac susceptibility, as expected for SMMs. We confirmed that 1 is a SMM with zero‐field quantum tunnelling of the magnetisation at 1.8 K. Compound 3 is likely a SMM with a blocking temperature well below 1.8 K. We established a physical model to fit the χT versus T and M versus B curves of the three compounds to reproduce the observed SMM trend. The analysis showed that small changes in the ligand shell modify not only the magnitude of exchange constants, but also affect the J and g matrices in a non‐trivial way.     

Development of Single‐Molecule Magnets†

Single‐molecule magnets (SMMs) are paramagnetic molecules that can be magnetized below a certain temperature and have potential applications in high‐density information storage, magnetic qubits, spintronic devices, etc. The discovery of the first SMM, Mn₁₂, opened a new era of molecular magnetism and promoted collaborative researches between chemists and physicists for their exotic quantum as well as classical magnetic properties. In the recent past, great efforts have been made to develop strategies for constructing new SMMs with high energy barriers (U_eff) and blocking temperatures (T_B), resulting in great and fast development of SMMs. In this concise review, we highlight the main synthetic approaches and representative results in the design and synthesis of high performance SMMs. We hope to give the readers a basic understanding of SMMs and a snapshot of the representative researches on SMMs from a perspective of synthetic chemists.     

Mono-, Di-, and Trimetallic Methacrylate-substituted Metal Oxide Clusters Derived from Hafnium Butoxide

The methacrylate-substituted clusters Hf₄O₂(OMc)₁₂, Hf₆O₄(OH)₄(OMc)₁₂(BuOH), Ti₄Hf₄O₆(OBu)₄(OMc)₁₆, and Ti₂Zr₅HfO₆(OMc)₂₀ (OMc=methacrylate) were prepared by reacting Hf(OBu)₄, or Hf(OBu)₄/Ti(OBu)₄ and Hf(OBu)₄/Zr(OBu)₄/Ti(OBu)₄ mixtures, respectively, with methacrylic acid. All clusters were characterized by X-ray structure analyses and are basically isostructural, although not in each case isomorphous, with the corresponding oxozirconium clusters. Low-temperature NMR studies revealed that the methacrylate ligands of Hf₄O₂(OMc)₁₂ are highly dynamic even at –80°C.     

Magnetic “Molecular Oligomers” Based on Decametallic Supertetrahedra: A Giant Mn49 Cuboctahedron and its Mn25Na4 Fragment

Two nanosized Mn₄₉ and Mn₂₅Na₄ clusters based on analogues of the high‐spin (S=22) [Mn^III₆Mn^II₄(μ₄‐O)₄]¹⁸⁺ supertetrahedral core are reported. Mn₄₉ and Mn₂₅Na₄ complexes consist of eight and four decametallic supertetrahedral subunits, respectively, display high virtual symmetry (O_h), and are unique examples of clusters based on a large number of tightly linked high nuclearity magnetic units. The complexes also have large spin ground‐state values (Mn₄₉: S=61/2; Mn₂₅Na₄: S=51/2) with the Mn₄₉ cluster displaying single‐molecule magnet (SMM) behavior and being the second largest reported homometallic SMM.