Dysprosiacarboranes as Organometallic Single-Molecule Magnets

The dicarbollide ion, nido-C₂B₉H₁₁²⁻ is isoelectronic with cyclopentadienyl. Herein, we make dysprosiacarboranes, namely [(C₂B₉H₁₁)₂Ln(THF)₂][Na(THF)₅] (Ln=Dy, 1Dy ) and [(THF)₃(μ-H)₃Li]₂[{η⁵-C₆H₄(CH₂)₂C₂B₉H₉}Dy{η²:η⁵-C₆H₄(CH₂)₂C₂B₉H₉}₂Li] 3Dy and show that dicarbollide ligands impose strong magnetic axiality on the central Dy^III ion. The effective energy barrier (U_eff) for the loss of magnetization can be varied by the substitution pattern on the dicarbollide. This finding is demonstrated by comparing complexes of nido-C₂B₉H₁₁²⁻ and nido-[o-xylylene-C₂B₉H₉]²⁻, which show a U_eff of 430(5) K and 804(7) K, respectively. The blocking temperature defined by the open hysteresis temperature of 3Dy reaches 6.8 K. Moreover, the linear complex [Dy(C₂B₉H₁₁)₂]⁻ is predicted to have comparable properties with the linear [Dy(Cp^Me3)₂]⁺ complex. As such, carboranyl ligands and their derivatives may provide a new type of organometallic ligand for high-performance single-molecule magnets.     

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。     

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.     

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.     

Radical-Bridged Heterometallic Single-Molecule Magnets Incorporating Four Lanthanoceniums

The syntheses and magnetic properties of organometallic heterometallic compounds [K(THF)₆]{Co^I[(μ₃-HAN)RE₂Cp*₄]₂} ( 1-RE ) and [K(Crypt)]₂{Co^I[(μ₃-HAN)RE₂Cp*₄]₂} ( 2-RE ) containing hexaazatrinaphthylene radicals (HAN⋅³⁻) and four rare earth (RE) ions are reported. 1-RE shows isolable species with ligand-based mixed valency as revealed by cyclic voltammetry (CV) thus leading to the isolation of 2-RE via one-electron chemical reduction. Strong electronic communication in mixed-valency supports stronger overall ferromagnetic behaviors in 2-RE than 1-RE containing Gd and Dy ions. Ac magnetic susceptibility data reveal 1-Dy and 2-Dy both exhibit slow magnetic relaxation. Importantly, larger coercive field was observed in the hysteresis of 2-Dy at 2.0 K, indicating the enhanced SMM behavior compared with 1-Dy . Ligand-based mixed-valency strategy has been used for the first time to improve the magnetic coupling in lanthanide (Ln) SMMs, thus opening up new ways to construct strongly coupled Ln-SMMs.     

Luminescent Single-Molecule Magnets as Dual Magneto-Optical Molecular Thermometers

Luminescent thermometry allows the remote detection of the temperature and holds great potential in future technological applications in which conventional systems could not operate. Complementary approaches to measuring the temperature aiming to enhance the thermal sensitivity would however represent a decisive step forward. For the first time, we demonstrate the proof-of-concept that luminescence thermometry could be associated with a complementary temperature readout related to a different property. Namely, we propose to take advantage of the temperature dependence of both magnetic (canonical susceptibility and relaxation time) and luminescence features (emission intensity) found in Single-Molecule Magnets (SMM) to develop original dual magneto-optical molecular thermometers to conciliate high-performance SMM and Boltzmann-type luminescence thermometry. We highlight this integrative approach to concurrent luminescent and magnetic thermometry using an air-stable benchmark SMM [Dy(bbpen)Cl] (H₂bbpen=N,N′-bis(2-hydroxybenzyl)-N,N′-bis(2-methylpyridyl)ethyl-enediamine)) exhibiting Dy³⁺ luminescence. The synergy between multiparametric magneto-optical readouts and multiple linear regression makes possible a 10-fold improvement in the relative thermal sensitivity of the thermometer over the whole temperature range, compared with the values obtained with the single optical or magnetic devices.     

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.     

Rational Improvement of Single-Molecule Magnets by Enforcing Ferromagnetic Interactions

The anisotropy barrier of polynuclear single-molecule magnets is expected to be higher with less tunneling the better stabilized the spin ground state is so that less M_S mixing in the ground state and with excited spin states occur. We have realized this experimentally in two structurally related heptanuclear SMMs: the triplesalen-based [Mn^III ₆ Cr^III]³⁺ and the triplesalalen-based *[Mn^III ₆ Cr^III]³⁺ . The ligand system triplesalen was developed to enforce ferromagnetic interactions by the spin-polarization mechanism. However, we found weak antiferromagnetic couplings, that we assigned to an inefficient spin-polarization by a heteroradialene formation. To prevent this heteroradialene formation, the triplesalalen ligand H₆talalen was designed. Here, we present the building block [(talalen )Mn^III₃]³⁺ and its application for the assembly of [{(talalen )Mn^III₃}₂{Cr^III(CN)₆}]³⁺ (= *[Mn^III ₆ Cr^III]³⁺ ). Both the trinuclear and heptanuclear complexes are SMMs. The comparison to the related triplesalen complex [(feld )Mn^III₃]³⁺ proves the absence of heteroradialene character and the enforcement of ferromagnetic Mn^III-Mn^III interactions in the (talalen )⁶⁻ complexes. This results in an increase of the barrier for spin reversal U_eff from 25 K in the triplesalen-based [Mn^III ₆ Cr^III]³⁺ SMMs to 37 K in the triplesalalen-based *[Mn^III ₆ Cr^III]³⁺ SMM proving the success of our concept. Based on this study, the next step in the rational improvement of our SMMs is discussed.     

Experimental Determination of Magnetic Anisotropy in Exchange-Bias Dysprosium Metallocene Single-Molecule Magnets

We investigate a family of dinuclear dysprosium metallocene single-molecule magnets (SMMs) bridged by methyl and halogen groups [Cp′₂Dy(μ-X)]₂ (Cp′=cyclopentadienyltrimethylsilane anion; 1 : X=CH₃⁻; 2 : X=Cl⁻; 3 : X=Br⁻; 4 : X=I⁻). For the first time, the magnetic easy axes of dysprosium metallocene SMMs are experimentally determined, confirming that the orientation of them are perpendicular to the equatorial plane which is made up of dysprosium and bridging atoms. The orientation of the magnetic easy axis for 1 deviates from the normal direction (by 10.3°) due to the stronger equatorial interactions between Dy^III and methyl groups. Moreover, its magnetic axes show a temperature-dependent shifting, which is caused by the competition between exchange interactions and Zeeman interactions. Studies of fluorescence and specific heat as well as ab initio calculations reveal the significant influences of the bridging ligands on their low-lying exchange-based energy levels and, consequently, low-temperature magnetic properties.     

Rare-Earth Metal Tetrathiafulvalene Carboxylate Frameworks as Redox-Switchable Single-Molecule Magnets

Using the redox-active tetrathiafulvalene tetrabenzoate (TTFTB⁴⁻) as the linker, a series of stable and porous rare-earth metal–organic frameworks (RE-MOFs), [RE₉(μ₃-OH)₁₃(μ₃-O)(H₂O)₉(TTFTB)₃] ( 1-RE , where RE=Y, Sm, Gd, Tb, Dy, Ho, and Er) were constructed. The RE₉(μ₃-OH)₁₃(μ₃-O) (H₂O)₉](CO₂)₁₂ clusters within 1-RE act as segregated single-molecule magnets (SMMs) displaying slow relaxation. Interestingly, upon oxidation by I₂, the S=0 TTFTB⁴⁻ linkers of 1-RE were converted into S= TTFTB^.3− radical linkers which introduced exchange-coupling between SMMs and modulated the relaxation. Furthermore, the SMM property can be restored by reduction in N,N-dimethylformamide. These results highlight the advantage of MOFs in the construction of redox-switchable SMMs.     

A Study of Magnetic Relaxation in Dysprosium(III) Single-Molecule Magnets

Although the development of single-molecule magnets (SMMs) is rapid, there are only two families of high energy barrier (U_eff) dysprosium(III) SMMs known so far: the cyclopentadienyl (Cp) family with a sandwich structure and the pentagonal-bipyramidal (PB) family with D_5h symmetry. These high-barrier SMMs, which usually possess U_eff>500 cm⁻¹ allow the separate study of the four magnetic relaxation paths, namely, direct, quantum tunnelling, Raman and Orbach processes, in detail. Whereas the first family is chemically more challenging to modify the Cp rings, it is shown herein that the latter family, with the common formulae [DyX¹X²(L_eq)₅]⁺, such as X¹/X²=⁻OCMe₃, ⁻OSiMe₃, ⁻OPh, Cl⁻ or Br⁻; L_eq=THF/pyridine/4-methylpyridine, can be readily fine-tuned with a range of axial and equatorial ligands by simple substitution reactions. This allows unambiguous confirmation that the U_eff mainly depends on the identity of X¹ and X², rather than on L_eq. More importantly, the fitted parameters are barrier dependent. If X¹ is an O donor and X² is a halide, 500<U_eff<600 cm⁻¹, log τ_0avg (s)=−10.66, log C_avg (s⁻¹ K⁻ⁿ)= −5.05, n_avg=4.1 and T_H=9 K (in which τ₀ is the pre-exponential factor for the Orbach relaxation process, C and n are parameters used to describe Raman relaxation, and T_H is the highest temperature at which magnetic hysteresis is observed). For cases in which both X¹ and X² are O donors, 900<U_eff<1300 cm⁻¹, log τ_0avg (s)=−11.63, log C_avg (s⁻¹ K⁻ⁿ)= −6.03, n_avg=4.1 and 18<T_H<25 K. Based on these results, it can be further concluded that U_eff not only has a linear correlation to the axial Dy−X bond lengths, but also to T_H for these PB SMMs. This represents the first systematic study of a family of lanthanide SMMs and derives the first magneto-structural correlation in Dy SMMs.     

Alkali Metal Based Triimidosulfite Cages as Versatile Precursors for Single-Molecule Magnets

Based on the potassium [{S(tBuN)₂(tBuNH)}₂K₃(tmeda)-K₃{(HNtBu)(NtBu)₂S}₂] ( 1 ) and sodium precursors [S(tBuN)₃(thf)₃-Na₃SNa₃(thf)₃(NtBu)₃S] ( 2 ), [S(tBuN)₃(thf)₃Na₃{(HNtBu)(NtBu)₂S}] ( 3 ) and [(tmeda)₃S-{Na₃(NtBu)₃S}₂] ( 4 ) the syntheses and magnetic properties of three mixed metal triimidosulfite based alkali-lanthanide-metal-cages [(tBuNH)Dy{K(0.5tmeda)}₂{(NtBu)₃S}₂]_n ( 5 ) and [ClLn{Na(thf)}₂{(NtBu)₃S}₂] with Ln=Dy ( 6 ), Er ( 7 ) are reported. The corresponding potassium ( 1 ) and sodium ( 2 – 4 ) based cages are characterized through XRD and NMR experiments. Preventing lithium chloride co-complexation led to a significant increase of SMM performance to previously reported sulfur-nitrogen ligands. The subsequent Dy^III-complexes 5 and 6 display slow relaxation of magnetization at zero field, with relaxation barriers U=77.0 cm⁻¹ for 5 , 512.9 and 316.3 cm⁻¹ for 6 , respectively. Significantly, the latter complex 6 also exhibits a butterfly-shaped hysteresis up to 7 K.     

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.     

基于席夫碱分隔配体的Cu-Tb单分子磁体的阴离子调控

基于席夫碱分隔配体H₂vanophen（1,2-苯二胺缩邻香草醛）,通过引入不同的阴离子,构筑了3个Cu-Tb基金属配合物[Cu₂（vanophen）₂TbCl₂（MeOH）₂]Cl·3MeOH（1）、[Cu₂（vanophen）₂TbCl₂（MeOH）₂]（TCNQ）_1.5·2MeOH（2）和[Cu₂（vanophen）₂Tb₂（N₃）₆]·2MeOH（3）（TCNQ=7,7,8,8-四氰基对苯二醌二甲烷）,并详细研究了它们的结构和磁性。除了抗衡阴离子外,配合物1和2具有非常相似的[CuTbCu]三核结构;其中Cu（Ⅱ）离子处于席夫碱配体中的[N₂O₂]配位口袋中,而Tb（Ⅲ）离子则和配体中的[O₄]配位口袋中的全部或部分O原子配位。对应于一个三核基元,配合物1中的抗衡阴离子为一个Cl^-离子,而配合物2中的抗衡阴离子是一个TCNQ^-0.5阴离子及半个TCNQ^-阴离子。配合物3是由end-end及end-on叠氮桥联2个[CuTb]单元形成的四核[CuTb]2配合物。磁性研究表明,三核配合物1和2均为场致的单分子磁体而配合物3为零场单分子磁体,其中配合物1和3的能垒分别为（11.1±0.3） cm^-1和（20.2±0.3） cm^-1。相比于配合物1,配合物2具有更低的能垒,这可能源于其中的阴离子自由基和三核[CuTbCu]基元之间的弱的磁相互作用。     

Photoluminescent Lanthanide(III) Single-Molecule Magnets in Three-Dimensional Polycyanidocuprate(I)-Based Frameworks

Three-dimensional bimetallic cyanido-bridged frameworks, [Ln^III(2,2′-bipyridine N,N′-dioxide)₂(H₂O)][Cu^I₂(CN)₅]⋅5 H₂O (Ln=Dy, 1 ; Yb, 2 ), are reported. They exhibit the effect of slow relaxation of magnetization, leading to a magnetic hysteresis loop, and sensitized visible-to-near-infrared photoluminescence. Both physical properties are related to the eight-coordinated lanthanide(III) complexes embedded in the unprecedented coordination skeleton composed of symmetry-breaking polycyanidocuprate linkers. The three-dimensional d–f cyanido-bridged network was shown to serve as an efficient coordination scaffold to achieve emissive lanthanide single-molecule magnets.     

Nanostructuring of Rare-earth-based Single-Molecule Magnets as Long-range Ordered Arrays in the Framework of Organic Metal Halide Perovskites

The nanostructuring of single-molecule magnets (SMMs) on substrates, in nanotubes and periodic frameworks is highly desired for the future magnetic recording devices. However, the ability to organize SMMs into long-range ordered arrays in these systems is still lacking. Here, we report the incorporation of magnetic (RECl₂(H₂O)₆)⁺ (RE=rare earths) molecular groups into the framework of an organic metal halide perovskite (OMHP)—(H₂dabco)CsCl₃. Intriguingly, we show the incorporated rare-earth groups self-organized into long-range ordered arrays that uniformly and periodically distributed in the A sites of OMHP. The ordered (RECl₂(H₂O)₆)⁺ groups serve as SMMs in the perovskite frameworks, exhibiting large effective magnetic moment, moderate magnetic anisotropy and two-step relaxation behavior. With the additional merit of great structural flexibility and multifunction of OMHPs, the preparation of the first SMMs@OMHP magnetic materials furthers the development of molecular spintronics.     

Single-Molecule Force Spectroscopy of DNA-Based Reversible Polymer Bridges: Surface Robustness and Homogeneity

Single-molecule force spectroscopy, as implemented in an atomic force microscope, provides a rarely used method by which to monitor dynamic processes that occur near surfaces. Here, a methodology is presented and characterized that facilitates the study of polymer bridging across nanometer-sized gaps. The model system employed is that of DNA-based reversible polymers, and an automated procedure is introduced that allows the AFM tip–surface contact point to be automatically determined, and the distance d between opposing surfaces to be actively controlled. Using this methodology, the importance of several experimental parameters was systematically studied, e.g. the frequency of repeated tip/surface contacts, the area of the substrate surface sampled by the AFM, and the use of multiple AFM tips and substrates. Experiments revealed the surfaces to be robust throughout pulling experiments, so that multiple touches and pulls could be carried out on a single spot with no measurable affect on the results. Differences in observed bridging probabilities were observed, both on different spots on the same surface and, more dramatically, from one day to another. Data normalization via a reference measurement allows data from multiple days to be directly compared.     

Electron－rich Polynuclear Transition Metal Clusters：Ⅰ． The Clusters with Chalcogen Bridges and Phosphine Ligands

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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。     

Role of Intermolecular Interactions in Formation of Linear Polynuclear Platinum Complexes

The electronic and steric structures of cis- and trans-[Pt(NH₃)₂Hlg₂] were calculated by HF and DFT methods, and the differences between their thermodynamic functions H ⁰ 298, S ⁰ 298, G ⁰ 298, and C _4p = f(T) were evaluated on the basis of DFT force fields. The differences between the stabilities of the cis and trans isomers are mainly due to features of molecular structure, namely, to the energy of interligand interaction. The nonvalent interactions Pt···Pt and NH₂-H···Hlg between the mononuclear fragments cis-[Pt(NH₃)₂· Hlg₂], weakening in the order Cl^- > Br^- > I^-, considerably enhance the stability of the cis isomers and provide conditions for formation of linear polynuclear complexes with Pt-Pt bonds.