单分子磁体

单分子磁体是涉及合成化学、材料科学和凝聚态物理等边缘学科的一个新颖课题。本文对单分子磁体的主要性质、功能、研究方法和最新进展做了评述。重点介绍了含Mn和Fe这两类重要的单分子磁体。     

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.     

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.     

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.     

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...     

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。     

杯芳烃修饰的六核镝单分子磁体

以对叔丁基杯[4]芳烃（HaC4A）配体合成了三个同构化合物[Ln^Ⅲ6（μ4-O）2（C4A）2（N03）2（HCOO）2-（CH30）2（DMF）4（CH30H）4]（Ln=Gd（1）,Tb（2）,Dy（3））,并对其晶体结构、磁性和荧光性质进行了研究．化合物结构中,两个尾对尾的杯芳烃分子和一个夹在中间的稀土八面体构成一个六核的三明治型结构单元,该结构单元通过超分子堆积形成化合物的三维结构．磁性和荧光测试表明,含镝化合物表现为具有光致发光性能的单分子磁体．     

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。     

脱水对六核锰单分子磁体磁性的影响

以水杨醛肟和Mn(CH3COO)2.4H2O为原料,合成了一个新的六核锰簇合物[Mn6O2(CH3COO)2(salox)6(H2O)4].10H2O(salox2-表示负二价的水杨醛肟),对其进行了单晶X射线衍射分析及脱水前后样品的直流和交流磁性测试。结果表明,该簇合物是一个反铁磁性单分子磁体,脱水使得六核锰簇内的反铁磁作用增强,磁弛豫能垒下降,但簇合物仍保持单分子磁体的性质。     

环形镧系分子簇合物的组装与单分子磁体性质

由于稀土离子具有很强的磁各向异性,近年来基于单核或多核稀土化合物的单分子磁体研究得到了人们广泛的关注.环形簇合物是一类特殊的簇合物,也称分子轮或金属冠醚.设计合成环形稀土簇合物不仅可以获得新的稀土单分子磁体,而且环形簇合物中稀土离子磁偶极的涡旋分布还可以产生环形磁矩,因而在量子计算、信息存储、自旋分子器件等方面具有潜在的应用.鉴于环形稀土簇合物特别是含奇数核的环形簇合物的合成依然充满挑战,本综述将着重阐述已报道的环形稀土簇合物的组装规律、结构特点及磁性研究.     

氰基桥联的Fe2Ni2单分子磁体的合成与磁性

利用三氰基构筑单元Bu₄N[Fe^Ⅲ（PzTp）（CN）₃]（PzTp=tetrakis（pyrazolyl）borate）和4,4''-二甲氧基-2,2''-联吡啶（4,4''-dmobpy）配体,合成了2例氰基桥联的Fe^Ⅲ₂Ni^Ⅱ₂四核配合物。单晶X射线衍射表明化合物[Fe^Ⅲ（PzTp）（CN）₃]₂[Ni^Ⅱ₂（4,4''-dmobpy）₄][Fe^Ⅲ（PzTp）（CN）₃]₂·2CH₃OH（1）和[Fe^Ⅲ（PzTp）（CN）₃]₂[Ni^Ⅱ₂（4,4''-dmobpy）₄]（PF₆）₂（2）具有四核四方形分子结构。直流磁化率测试表明配合物1和2均表现为分子内的铁磁耦合作用。交流磁化率测试表明配合物1和2在零场下具有慢磁弛豫行为,有效能垒分别为12.8和13.0 K。     

Axial Elongation of Mononuclear Lanthanide Metallocenophanes: Magnetic Properties of Dysprosium- and Terbium-[1]Ruthenocenophane Complexes

We report the first f-block-ruthenocenophane complexes 1 (Dy) and 2 (Tb) and provide a comparative discussion of their magnetic structure with respect to earlier reported ferrocenophane analogues. While axial elongation of the rare trigonal-prismatic geometry stabilizes the magnetic ground state in the case of Dy³⁺ and results in a larger barrier to magnetization reversal (U), a decrease in U is observed for the case of Tb³⁺.     

Axial Elongation of Mononuclear Lanthanide Metallocenophanes: Magnetic Properties of Dysprosium‐ and Terbium‐[1]Ruthenocenophane Complexes

We report the first f‐block‐ruthenocenophane complexes 1 (Dy) and 2 (Tb) and provide a comparative discussion of their magnetic structure with respect to earlier reported ferrocenophane analogues. While axial elongation of the rare trigonal‐prismatic geometry stabilizes the magnetic ground state in the case of Dy³⁺ and results in a larger barrier to magnetization reversal (U), a decrease in U is observed for the case of Tb³⁺.     

Identification of Favorable Silica Surface Sites for Single-Molecule Magnets

Industrial data storage application based on single-molecule magnets (SMMs) necessitates not only strong magnetic remanence at high temperatures but also requires the implementation of SMMs into a solid material to increase their durability and addressability. While the understanding of the relationship between the local structure of the metal and the resulting magnetic behavior is well understood in molecular systems, it remains challenging to establish a similar understanding for magnetic materials, especially for isolated lanthanide sites on surfaces. For instance, dispersed Dy(III) ions on silica prepared via surface organometallic chemistry exhibit slow magnetic relaxation at low temperatures, but the origin of these properties remains unclear. In this work, we modelled ten neutral complexes with coordination numbers (CN) between three and six ([Dy(OSiF₃)₃(O(SiF₃)₂)_CN-3]) representing possible surface sites for dispersed Dy(III) ions and investigated their SMM potential via ab initio CASSCF/RASSI-SO calculations. Detailed analysis of the data shows the strong influence of the spatial position of the anionic ligands while the neutral ligands only play a minor role for the magnetic properties. In particular, a T-shape like orientation of the anionic ligands is predicted to exhibit good SMM properties making it a promising targeted coordination environment for molecular and surface-based SMMs.     

生物单分子力谱技术的研究进展

近年来,单分子力谱技术获得了快速发展和广泛应用。通过单分子力谱技术研究生物分子结构、力学及动力学,在单分子水平上揭示生物分子间相互作用机制,对于深入了解生物分子的特异识别、生化过程以及生物分子结构与功能的关系具有重要意义。本文主要介绍了3种最常见的单分子力谱技术:原子力显微镜(AFM),光镊(OT)和磁镊(MT)。另外,还侧重从不同力谱技术的原理、发展及应用三个方面简要介绍了3种大规模并行测量的单分子力谱技术:声力谱(AFS)、离心力显微镜(CFM)以及力诱导剩磁谱技术(FIRMS)。     

单分子电泳:纳米孔道电化学的新认识

该文旨在从电泳分离技术的角度认识纳米孔道电化学单分子分析技术,这种技术可以作为"单分子电泳"来理解和研究。纳米孔道电化学单分子分析技术与电泳的本质都是采用外加电场使待测分子产生电迁移。待测分子性质不同,且与介质材料孔道外露基团相互作用不同,使得分子移动速度具有差异,据此实现分离识别。气单胞菌溶素(Aerolysin)纳米孔道,由于其孔径与待测分子尺寸相匹配,其孔道内壁可以看作是由氨基酸组成的具有调控单个分子电迁移能力的特异性孔道界面。每一个氨基酸残基都相当于一个探测单元,在电场力的作用下,待测分子逐一进入孔道时与每一个探测单元相互作用方式、程度与时长不同,从而形成了单个待测分子特征的迁移速度和迁移运动轨迹。在纳米孔道实验中,每秒可以有上千个待测分子穿过孔道,产生特征阻断电流信号。通过对这些信号的阻断电流、阻断时间、阻断频率、信号特征等进行统计分析,可以从"单分子电泳"水平对单个待测物实现高通量的分辨和识别。该文以Aerolysin纳米孔道分辨仅有一个核苷酸差异的寡聚核苷酸(5′-CAA-3′、5′-CAAA-3′、5′-CAAAA-3′)为例,详细阐述了纳米孔道"单分子电泳"的单核苷酸...     

Mononuclear Dysprosium Alkoxide and Aryloxide Single-Molecule Magnets

Recent studies have shown that mononuclear lanthanide (Ln) complexes can be high-performing single-molecule magnets (SMMs). Recently, there has been an influx of mononuclear Ln alkoxide and aryloxide SMMs, which have provided the necessary geometrical control to improve SMM properties and to allow the intricate relaxation dynamics of Ln SMMs to be studied in detail. Here non-aqueous Ln alkoxide and aryloxide chemistry applied to the synthesis of low-coordinate mononuclear Ln SMMs are reviewed. The focus is on mononuclear Dy^III alkoxide and aryloxide SMMs with coordination numbers up to eight, covering synthesis, solid-state structures and magnetic attributes. Brief overviews are also provided of mononuclear Tb^III, Ho^III, Er^III and Yb^III alkoxide and aryloxide SMMs.     

Preparation of Polyaniline Nanotubes via “Thin Glass Tubes Template” Approach and its Gas Response

PANI nanotubes were successfully prepared by using thin glass tubes as a single template in the presence of H₄SiW₁₂O₄₀ and ammonium persulfate, which were used as dopant and oxidant, respectively, in this system. The structure and morphology of the PANI were characterized by IR spectrum, XRD pattern, SEM images, and TEM images. The inner diameter of PANI nanotubes was between 50 and 100 nm. This method employed here was a simple and effective way to prepare multifunctional PANI nanotubes. The gas response of the PANI nanotubes to a series of chemical vapors such as NH₃, N₂H₄, and (C₂H₅)₃N was studied. The results indicate that the PANI nanotubes show superior performance as chemical sensor.

     

Probing Relaxation Dynamics in Five-Coordinate Dysprosium Single-Molecule Magnets

A new family of five-coordinate lanthanide single-molecule magnets (Ln SMMs) [Dy(Mes*O)₂(THF)₂X] (Mes*=2,4,6-tri-tert-butylphenyl; X=Cl, 1 ; Br, 2 ; I, 3 ) is reported with energy barriers to magnetic reversal >1200 K. The five-coordinate Dy^III ions have distorted square pyramidal geometries, with halide anions on the apex, and two Mes*O ligands mutually trans- to each other, and the two THF molecules forming the second trans- pair. These geometrical features lead to a large magnetic anisotropy in these complexes along the trans-Mes*O direction. QTM and Raman relaxation times are enhanced by varying the apex halide from Cl to Br to I, or by dilution in a diamagnetic yttrium analogue.     

Heterometallic 3d–4f Complexes as Single‐Molecule Magnets

Heterometallic 3d‐4f complexes are being investigated, for some time, as being useful in molecular magnetism, particularly as single‐molecule magnets (SMMs). This interest is primarily because of the possibility of an increased ligand‐mediated super‐exchange phenomenon between the 3d and 4f metal ions. Such an interaction, apart from bestowing a favorable ground‐state spin to the complex, also assists in reducing quantum tunneling of magnetization that is widely prevalent in SMMs making them to lose magnetization. However, assembling both 3d as well as 4f ions using same ligand system is challenging and involves the design of multi‐site coordination ligands with specific coordination compartments for the 3d and the 4f metal ions while at the same time allowing these disparate metal ions to be linked to each other through a bridging ligating atom. This review presents a summary of the 3d‐4f complexes primarily derived from the author's work while alluding to important examples from the literature. We also provide an outlook for the future design of such complexes.