Heterometallic Rings: Their Physics and use as Supramolecular Building Blocks

An enormous family of heterometallic rings has been made. The first were Cr₇M rings where M=Ni^II, Zn^II, Mn^II, and rings have been made with as many as fourteen metal centers in the cyclic structure. They are bridged externally by carboxylates, and internally by fluorides or a penta‐deprotonated polyol. The size of the rings is controlled through templates which have included a range of ammonium or imidazolium ions, alkali metals and coordination compounds. The rings can be functionalized to act as ligands, and incorporated into hybrid organic–inorganic rotaxanes and into molecules containing up to 200 metal centers. Physical studies reported include: magnetic measurements, inelastic neutron scattering (including single crystal measurements), electron paramagnetic resonance spectroscopy (including measurements of phase memory times), NMR spectroscopy (both solution and solid state), and polarized neutron diffraction. The rings are hence ideal for understanding magnetism in elegant exchange‐coupled systems.     

[Fe19] “Super‐Lindqvist” Aggregate and Large 3D Interpenetrating Coordination Polymer from Solvothermal Reactions of [Fe2(OtBu)6] with Ethanol

The syntheses, crystal structures, and physical properties of [HFe₁₉O₁₄(OEt)₃₀] and {Fe₁₁(OEt)₂₄}_∞ are reported. [HFe₁₉O₁₄(OEt)₃₀] has an octahedral shape. Its core with a central Fe metal ion surrounded by six μ₆‐oxo ligands is arranged in the rock salt structure. {Fe₁₁(OEt)₂₄}_∞ is a mixed‐valence coordination polymer in which Fe^III metal ions form three 3D interpenetrating (10,3)‐b nets. The arrangement of the Fe^III ions can also be compared to that of Si ions in α‐ThSi₂. Thus, the described structures are at the interface between molecular and solid‐state chemistry.     

A Cobalt Pyrenylnitronylnitroxide Single‐Chain Magnet with High Coercivity and Record Blocking Temperature

Coordination of a [Co(hfac)₂] moiety (hfac=hexafluoroacetylacetonate) with a nitronylnitroxide radical linked to bulky, rigid pyrene (PyrNN) gives a helical 1:1 chain complex, in which both oxygen atoms of the radical NO^. groups are bonded to Co^II ions with strong antiferromagnetic exchange. The complex shows single‐chain magnet (SCM) behavior with frequency‐dependent magnetic susceptibility, field‐cooled and zero‐field‐cooled susceptibility divergence with a high blocking temperature of around 14 K (a record among SCMs), and hysteresis with a very large coercivity of 32 kOe at 8 K. The magnetic behavior is partly related to good chain isolation induced by the large pyrene units. Two magnetic relaxation processes have been observed, a slower one attributable to longer, and a faster one attributable to short chains. No evidence of magnetic ordering has been found.     

Angular‐Resolved Magnetometry Beyond Triclinic Crystals Part II: Torque Magnetometry of Cp*ErCOT Single‐Molecule Magnets

The experimental investigation of the molecular magnetic anisotropy in crystals in which the magnetic centers are symmetry related, but do not have a parallel orientation has been approached by using torque magnetometry. A single crystal of the orthorhombic organometallic Cp*ErCOT [Cp*=pentamethylcyclopentadiene anion (C₅Me₅^?); COT=cyclooctatetraenedianion (C₈H₈^2?)] single‐molecule magnet, characterized by the presence of two nonparallel families of molecules in the crystal, has been investigated above its blocking temperature. The results confirm an Ising‐type anisotropy with the easy direction pointing along the pseudosymmetry axis of the complex, as previously suggested by out‐of‐equilibrium angular‐resolved magnetometry. The use of torque magnetometry, not requiring the presence of magnetic hysteresis, proves to be even more powerful for these purposes than standard single‐crystal magnetometry. Furthermore, exploiting the sensitivity and versatility of this technique, magnetic anisotropy has been investigated up to 150 K, providing additional information on the crystal‐field splitting of the ground J multiplet of the Er^III ion.     

A family of hexanuclear Mn(III) single-molecule magnets

In an attempt to employ salicylic acid (HOsalH), 2,6-dihydroxy benzoic acid {(HO)₂PhCO₂H}, and naphthalene-1,8-dicarboxylic acid {1,8-naph(CO₂H)₂} in Mn(III) salicylaldoximate chemistry as a means to alter the structural identity of the hexanucluear clusters usually obtained from this reaction system, we have isolated a family of hexanuclear Mn(III) complexes based on salicyladloxime (saoH₂) and 2-hydroxy-1-naphthaldehyde oxime (naphthsaoH₂). Five hexanuclear clusters, [Mn₆O₂(sao)₆(HOsal)₂(EtOH)₄]·EtOH (1·EtOH), [Mn₆O₂(sao)₆{1,8-naph(CO₂Me)(CO₂)}₂(MeOH)₆]·3MeOH (2·3MeOH), [Mn₆O₂(naphthsao)₆{1,8-naph(CO₂Et)(CO₂)}₂(EtOH)₆] (3·2MeOH), [Mn₆O₂(naphthsao)₆(MeCO₂)₂(EtOH)₄]·2H₂O (4·2H₂O), and [Mn₆O₂(naphthsao)₆{(HO)₂PhCO₂}₂(EtOH)₄]·4EtOH (5·4EtOH), have been synthesized and characterized by single-crystal X-ray crystallography. The magnetic properties of 3, 4, and 5 are discussed.     

A Trigonal‐Pyramidal Erbium(III) Single‐Molecule Magnet

Given the recent advent of mononuclear single‐molecule magnets (SMMs), a rational approach based on lanthanides with axially elongated f‐electron charge cloud (prolate) has only recently received attention. We report herein a new SMM, [Li(THF)₄[Er{N(SiMe₃)₂}₃Cl]?2 THF, which exhibits slow relaxation of the magnetization under zero dc field with an effective barrier to the reversal of magnetization (ΔE_eff/k_B=63.3 K) and magnetic hysteresis up to 3 K at a magnetic field sweep rate of 34.6 Oe s^?1. This work questions the theory that oblate or prolate lanthanides must be stabilized with the appropriate ligand framework in order for SMM behavior to be favored.     

Two‐Coordinate Iron(I) Complex [Fe{N(SiMe3)2}2]−: Synthesis,Properties, and Redox Activity

First‐row two‐coordinate complexes are attracting much interest. Herein, we report the high‐yield isolation of the linear two‐coordinate iron(I) complex salt [K(L)][Fe{N(SiMe₃)₂}₂] (L=18‐crown‐6 or crypt‐222) through the reduction of either [Fe{N(SiMe₃)₂}₂] or its three‐coordinate phosphine adduct [Fe{N(SiMe₃)₂}₂(PCy₃)]. Detailed characterization is gained through X‐ray diffraction, variable‐temperature NMR spectroscopy, and magnetic susceptibility studies. One‐ and two‐electron oxidation through reaction with I₂ is further found to afford the corresponding iodo iron(II) and diiodo iron(III) complexes.     

非磁性纳米SiO2颗粒在磁场流化床中的流态化

研究了非磁性纳米SiO2颗粒在添加磁性大颗粒磁场流化床中的流化性能。磁性大颗粒的添加量在20%～60%(wt)之间,磁感应强度的大小分别为0.0477、0.0596、0.0715 T。实验中通过测定床层膨胀曲线、床层压降曲线,详细地考察了磁性大颗粒的添加量、磁感应强度及气速的大小对纳米SiO2颗粒流化性能的影响。结果表明:把磁场能引入普通流化床中之后,加入的磁性粗颗粒能够有效地破碎纳米SiO2床层中的活塞、沟流和大聚团,降低最小流化速度,且在最小流化速度时无气泡,使床层膨胀比增加,提高床层的整体流化质量;在流化颗粒相中,磁场能的加入还可以保持床层的稳定性,维持流态化所需的气体体积。     

Single-molecule magnet behaviour in a tetrathiafulvalene-based electroactive antiferromagnetically coupled dinuclear dysprosium(III) complex

The reactions between the [Ln(tta)(3)]·2H(2)O precursors (tta(-)=2-thenoyltrifluoroacetonate anion) and the tetrathiafulvalene-3-pyridine-N-oxide ligands (L(1)) lead to dinuclear complexes of formula [{Ln(tta)(3)(L(1))}(2)]·xCH(2)Cl(2) (x=0.5 for Ln=Dy(III) (1) and x=0 for Ln=Gd(III) (2)). The crystal structure reveals that two {Ln(tta)(3)} moieties are bridged by two donors through the nitroxide groups. The Dy(III) centre adopts a distorted square antiprismatic oxygenated polyhedron structure. The antiferromagnetic nature of the exchange interaction between the two Dy(III) ions has been determined by two methods: 1) an empirical method using the [Dy(hfac)(3)(L(2))(2)] mononuclear complex as a model (3) (hfac(-)=1,1,1,5,5,5-hexafluoroacetylacetonate anion, L(2)=tetrathiafulvaleneamido-2-pyridine-N-oxide ligand), and 2) assuming an Ising model for the Dy(III) ion giving an exchange energy of -2.30 cm(-1), g=19.2 in the temperature range of 2-10 K. The antiferromagnetic interactions have been confirmed by a quantitative determination of J for the isotropic Gd(III) derivative (J=-0.031 cm(-1), g=2.003). Compound 1 displays a slow magnetisation relaxation without applied external magnetic fields. Alternating current susceptibility shows a thermally activated behaviour with pre-exponential factors of 5.48(4)×10(-7) s and an energy barrier of 87(1) K. The application of an external field of 1.6 kOe compensates the antiferromagnetic interactions and opens a new quantum tunnelling path.     

Substrate‐Independent Magnetic Bistability in Monolayers of the Single‐Molecule Magnet Dy2ScN@C80 on Metals and Insulators

Magnetic hysteresis is demonstrated for monolayers of the single‐molecule magnet (SMM) Dy₂ScN@C₈₀ deposited on Au(111), Ag(100), and MgO|Ag(100) surfaces by vacuum sublimation. The topography and electronic structure of Dy₂ScN@C₈₀ adsorbed on Au(111) were studied by STM. X‐ray magnetic CD studies show that the Dy₂ScN@C₈₀ monolayers exhibit similarly broad magnetic hysteresis independent on the substrate used, but the orientation of the Dy₂ScN cluster depends strongly on the surface. DFT calculations show that the extent of the electronic interaction of the fullerene molecules with the surface is increasing dramatically from MgO to Au(111) and Ag(100). However, the charge redistribution at the fullerene‐surface interface is fully absorbed by the carbon cage, leaving the state of the endohedral cluster intact. This Faraday cage effect of the fullerene preserves the magnetic bistability of fullerene‐SMMs on conducting substrates and facilitates their application in molecular spintronics.