三个镧系金属氮氧自由基配合物的合成、结构及磁性

以氮氧自由基为配体,合成了3例氮氧自由基-稀土三自旋单核配合物[Ln（hfac）₃（NIT-Ph-4-Br）₂]（Ln=Gd（1）,Tb（2）,Dy（3）,hfac=六氟乙酰丙酮,NIT-Ph-4-Br=4,4,5,5-四甲基-2-（4''-溴）-咪唑啉-3-氧化-1-氧基自由基。单晶结构分析表明3个配合物均属单斜晶系P2₁/c空间群,配合物中的Ln（Ⅲ）离子为八配位模式,并且拥有相似的自由基-稀土-自由基单核结构。对配合物的磁性测试结果表明,配合物1中自由基与Gd（Ⅲ）离子之间存在着铁磁相互作用,自由基与自由基之间存在着反铁磁相互作用;配合物2,3中,稀土离子与自由基之间存在弱的反铁磁相互作用。     

含羟基基团取代的氮氧自由基构筑的三个双核稀土化合物的结构及磁性表征

以三氟乙酰丙酮(tfac)为共配体的稀土配合物分别与5-溴-2-羟基苯取代的自由基配体和5-硝基-2-羟基苯取代的自由基配体进行反应,合成3个稀土-自由基配合物[Ln2(tfac)4(NIT-5Br-2PhO)2](Ln=Gd (1),Dy(2))和[Dy2(tfac)4(NIT-5NO2-2PhO)2](3)(NIT...     

Exchange Interaction of a Novel Heterospin Polynuclear Complex Containing Transition Metals and Imino Nitroxide Radicals: {[(CuL)Nid (IM‐2Py)2] (C104)2}2·2H2O

A novel heterospin complex {[(CuL) Ni(IM‐2Py)₂] (ClO₄)₂}₂· 2H₂O (L = 2,3‐dioxo‐5,6:14, 15‐dibenzo‐1,4,8,12‐tetraazacyclo‐pentadeca 7, 12‐diene, IM‐2Py = 2‐(2′‐pyridyl)‐4, 4, 5, 5‐tetramethyl‐4, 5‐dihydro‐1H‐imidazoline‐1‐oxyl) has been synthesized and its crystal structure was determined by X‐ray diffraction analysis. In order to interpret the exchange interaction of tins asymmetric heterospin system, a theoretical model has been established. Using this theoretical model the magnetic susceptibility data have been fitted and lead to coupling constant values equal to 1.4 cm^?1 (Ni‐Rad) and‐38.0 cm^?1(Ni‐Cu), respectively.     

Magnetic Anisotropy in a Family of Experimentally Synthesized and Theoretically Modeled M′6M8(CN24) Systems

A theoretical density functional study of the magnetic coupling interactions and magnetic anisotropy in a family of experimentally synthesized and theoretically modeled M′₆M₈(CN₂₄) (M′=Cu^II, Ni^II or Co^II; M=Fe^III or Cr^III) systems is presented. The calculations show that the interactions in the selected M′₆M₈(CN₂₄) are all ferromagnetic and the near cubic symmetry of Cu₆Fe₈ is the origin of its negative magnetic anisotropy parameter D.     

Magnetic Blocking from Exchange Interactions: Slow Relaxation of the Magnetization and Hysteresis Loop Observed in a Dysprosium–Nitronyl Nitroxide Chain Compound with an Antiferromagnetic Ground State

The combination of the anisotropic Dy^III ion and organic radicals as spin carriers results in discrete and one‐dimensional lanthanide–radical magnetic materials, namely, [Dy(hfac)₃(NITThienPh)₂] ( 1 ) and [Dy₂(hfac)₆(NITThienPh)₂]_n ( 2 ; hfac=hexafluoroacetylacetonate, NITThienPh=2‐(5‐phenyl‐2‐thienyl)‐4,4,5,5‐tetramethyl‐imidazoline‐1‐oxyl‐3‐oxide). Linking monomeric 1 with the Dy^III ion leads to the formation of polymeric 2 , and the transformation between them is chemically controllable and reversible. The characterization of both static and dynamic magnetic properties shows that the dominant intrachain exchange interaction is important to observe magnetic bistability in 2 rather than that in 1 . Monomeric 1 exhibits paramagnetic behavior, whereas polymeric 2 shows the unusual coexistence of superparamagnetic and two‐step field‐induced metamagnetic behaviors. The antiferromagnetic ground state of 2 does not prevent the dynamic relaxation of the magnetization with the finite‐sized effect in the lanthanide–radical system. Energy barriers to thermally activated relaxation for 2 are 53 and 98 K in the low‐ and high‐temperature regimes, respectively. A hysteresis loop is observed with the coercive field of 99 Oe at 2 K.     

Large Hexadecametallic {MnIII–LnIII} Wheels: Synthesis,Structural, Magnetic,and Theoretical Characterization

The synthesis, gas sorption studies, magnetic properties, and theoretical studies of new molecular wheels of core type {Mn^III₈Ln^III₈} (Ln=Dy, Ho, Er, Y and Yb), using the ligand mdeaH₂, in the presence of ortho‐toluic or benzoic acid are reported. From the seven wheels studied the {Mn₈Dy₈} and {Mn₈Y₈} analogues exhibit SMM behavior as determined from ac susceptibility experiments in a zero static magnetic field. From DFT calculations a S=16 ground state was determined for the {Mn₈Y₈} complex due to weak ferromagnetic Mn^III–Mn^III interactions. Ab initio CASSCF+RASSI‐SO calculations on the {Mn₈Dy₈} wheel estimated the Mn^III–Dy^III exchange interaction as ?0.1 cm^?1. This weak exchange along with unfavorable single‐ion anisotropy of Dy^III/Mn^III ions, however, led to the observation of SMM behavior with fast magnetic relaxation. The orientation of the g‐anisotropy of the Dy^III ions is found to be perpendicular to the plane of the wheel and this suggests the possibility of toroidal magnetic moments in the cluster. The {Mn₈Ln₈} clusters reported here are the largest heterometallic Mn^IIILn^III wheels and the largest {3d–4f} wheels to exhibit SMM behavior reported to date.     

Host–Guest [2+2] Cycloaddition Reaction: Postsynthetic Modulation of CO2 Selectivity and Magnetic Properties in a Bimodal Metal–Organic Framework

Simultaneous tuning of permanent porosity and modulation of magnetic properties by postsynthetic modification (PSM) with light in a metal–organic framework is unprecedented. With the aim of achieving such a photoresponsive porous magnetic material, a 3D photoresponsive biporous framework, MOF1, which has 2D channels occupied by the guest 1,2‐bis(4‐pyridyl)ethylene (bpee), H₂O, and EtOH molecules, has been synthesized. The guest bpee in 1 is aligned parallel to pillared bpee with a distance of 3.9 Å between the ethylenic groups; this allows photoinduced PSM of the pore surface through a [2+2] cycloaddition reaction to yield MOF2. Such photoinduced PSM of the framework structure introduces enhanced CO₂ selectivity over that of N₂. The higher selectivity in MOF2 than that of MOF1 is studied through theoretical calculations. Moreover, MOF2 unveils reversible changes in T_c with response to dehydration–rehydration. This result demonstrates that photoinduced PSM is a powerful tool for fabricating novel functional materials.