【作者】 张盛；

【导师】 陈三平；

【作者基本信息】 西北大学 ， 材料化学， 2016， 博士

【摘要】 分子纳米磁体在高密度信息存储、量子计算、分子自旋原件等方面具有潜在的应用前景,其中稀土分子纳米磁体的设计合成及性质研究是当前分子磁性的研究热点。本论文旨在探索影响稀土金属分子基磁体磁学行为的因素,寻找拥有高“阻塞”温度(TB,blocking temperature)及翻转能垒(Ueff)的单分子磁体的合成策略以及理论依据。选择具有强旋轨耦合,即可以产生强磁各向异性的稀土金属Dy和Er为自旋中心,与β-二酮类配体以及螯合配位模式的辅助配体构筑[LnN206](Ln=Dy,Er)型的单核配合物,选择铵盐作为抗衡阳离子构筑合成[Dy08]型的单核配合物,讨论了溶剂效应、构型以及抗衡阳离子对单核单分子磁体的磁动力学的影响。此外,研究了具有慢磁弛豫行为的金属有机框架类配合物的磁构关系,并采用席夫碱类与苯甲酸构筑合成了双核镝单分子磁体,并讨论了桥联配体以及金属构型对于磁体行为的影响。具体研究内容和研究结果如下：1.第二章,基于三种β-二酮和辅助配体构筑了五例[DyN206]型单核金属镝(Ⅲ)配合物,分别为[Dy(5-N02-Phen)(tfmb)3](1,tf-mb=4,4,4-三氟-1-(4-甲苯基)-1,3-丁二酮,5-NO2-Phen=5-硝基-1,10-邻二氮菲)、[Dy(DMF)2(tffb)3](2,tffb=4,4,4-三氟-1-(4-氟苯基)-1,3-丁二酮)、[Dy(bpy)2(tfnb)3]’0.5C4H8O2(3,tfnb:4,4,4-三氟-1-(2-奈基)-1,3-丁二酮)、[Dy(bpy)2(tffb))3]·(C4H802)1/3(4,bpy=2,2’-联吡啶)以及[Dy(Phen)2(tffb)3](5,Phen=1,10-邻二氮菲)。从结构来看,1-5的畸变程度按照3>2>4≈1>5的顺序变化。相邻金属之间的最短距离分别为10.035 A,8.750 A,10.035 A,9.019 A以及9.679 A。磁性研究表明,无外加直流场情况下,配合物1-4的虚部均表现出了弱的温度依赖的交流磁化率信号,而配合物5表现出了强的信号。外加1200Oe的直流场下,配合物1-5的量子隧穿效应得到有效抑制,拟合得到有效能垒(△E/kB)的顺序为5(91.70 K)>4(87.31 K)>1(82.93 K)>2(55.36 K)>3(38.66 K)。有趣的是,配合物2频率依赖的交流磁化率出现了两个弛豫过程,分别归属为快弛豫过程(FR)以及慢磁弛豫过程(SR)。配合物4和5分别在2.2 K以及2.0 K时出现了蝴蝶状的磁滞回线。2.第三章,探究了溶剂效应对于构型以及磁动力学行为的调控。比较单核配合物[Dy(Phen)(tfmb)3](6)与[Dy(Phen)(tfmb)3]·0.5C4H8O2(7)以及Dy(bpy)(tfmb)3](8)与[Dy(bpy)(tfmb)3]·0.5C4H8O2 (9)在有无溶剂情况下的结构变化以及磁性变化。从能垒和弛豫时间上对比发现,配合物7要优于配合物6,而配合物9要优于8。研究发现除了金属离子的构型外,弱的相互作用力导致的不同的耦极耦极相互也是影响磁性的重要因素。3.第四章,选择不同的抗衡阳离子,得到了三例β二酮类[Dy08]型四方反棱柱构型的单核配合物,[Hthyl3N][Dy(tffb)4] (10, Hthyl3N=三乙胺), [Butyl4N][Dy(tfnb)4] 11,Butyl4NBr=四丁基溴化铵)[Hthyl3N][Dy(dbma)4] (12, Hthyl3N=三乙胺)磁性研究发现,这三个配合物均表现出了场诱导的单核单分子磁体行为。通过与文献中类似配合物比较,发现不同空间位阻的季铵盐对于磁性也会产生一定的调控作用。4.第五章,合成了单核配合物[Er(Phen)(tfmb)3] (13)与[Er(Phen)(tfnb)3] (14),并对它们进行了结构和磁性表征,考察不同的二酮配体对于四方反棱柱构型的金属Er单核配合物磁性的影响。5.第六章,以草酸与金属镝构筑了二维镝层状配合物,[Dy(C2O4)15(H2O)3]·2nH2O(15)。结构显示,金属镝离子处于三帽三棱柱构型中,邻近的金属离子通过草酸根以μ2-KO,O’的双桥联方式连接。磁学表征显示,在700 Oe的直流场下,配合物15表现出了双弛豫过程,归属为快弛豫和慢弛豫过程,对应的能垒和弛豫时间为3.8 K,4.3×10-2 s与10.7 K,4.39×10-6 s,分别归因为金属Dy离子自身的磁各向异性以及外加磁场或是耦极耦极相互作用加强量子隧穿效应所致。并与文献中类似配合物进行了比较,进一步讨论了磁构关系。另有,通过Dy(PhCOO)3与多齿配位的席夫碱配体1,5-二(2-羟基-3-甲氧基苯亚甲基)碳酰肼(H4L)反应得到了一个双核镝单元的配合物,[Dy2(H3L)2(PhCOO)4]·4H2O (16),结构显示,金属离子同样处于一个三帽三棱柱构型中,邻近的金属离子由羧基采用μ:η1,η2的配位模式以及羟基氧采用μ:η2的配位模式桥联形成,并讨论了桥联方式以及金属离子构型对于磁体性质的影响。更多还原

【Abstract】 This paper focuses on exploring influence factors, the synthesis strategy and theoretical basis of the single molecule magnets (SMMs) to obtain high blocking temperature (TB) and large energy barrier to magnetization reversal (Ueff)-In present, the best candidate of these molecular materials is Dy (Ⅲ) and Er (Ⅲ) ions due to the inherent strong spin-orbital coupling effect and hence very large magnetic anisotropy of the 6H15/2 and 4H15/2 ground state. Herein, we obtained a serious of mononuclear [LnN2O6] (Ln= Dy (Ⅲ) or Er (Ⅲ)) complexes based on different β-diketonate ligands and auxiliary Ligands, exhibiting approximately square-antiprismatic (SAP) N2O6 coordination environment with D44 axial symmetry. Based on counter cations, mononuclear [DyOg] dysprosium(Ⅲ) complexes were synthesized. The effects of solvent effect, configuration and counter cations on the magnetic dynamics of mononuclear single molecule magnets were discussed. Additionally, a nine-coordinated dysprosium (Ⅲ) compound with the oxalate-bridged dysprosium (Ⅲ) layer was obtained, exhibiting two slow magnetic relaxation processes and a Dy2 single-molecule magnet (SMM) with the benzoate anions and phenol-O- bridging groups was synthesized and characterized. The structure-property relationship of some selected Dy2 paradigmatic compounds was further discussed. The specific contents are as follows:1. Five mononuclear dysprosium (Ⅲ) complexes were synthesized based on three β-diketonate ligands,4,4,4-Trifluoro-l-(4-methylphenyl)-1,3-butanedione (tfmb), 4,4,4-Trifluoro-1-(4-fluorophenyl)-1,3-butanedione (tffb) and 4,4,4-Trifluoro-l-(2-naphthyl)-1,3-butanedione (tfnb) as well as auxiliary ligands, 1,10-phenanthroline (Phen),5-Nitro-1,10-phenanthroline (5-NO2-Phen), DMF and 2,2’-bipyridine (bpy), namely, [Dy(5-NO2-Phen)(tfmb)3] (1), [Dy(DMF)2(tfmb)3] (2) and [Dy(bpy)2(tfnb)3]-(1,4-dioxane)1/2 (3), [Dy(bpy)2(tffb)3]-(1,4-dioxane)1/3 (4) and [Dy(Phen)2(tffb)3] (5). In 1-5, the Dy (Ⅲ) ions exhibit approximately square-antiprismatic (SAP) N2O6 coordination environment with D4d axial symmetry. According to the Dy (Ⅲ) coordination spheres of 1-5, these complexes are slightly distorted with the following order:3 >2>4=1>5. The shortest intermolecular distances between Dy (Ⅲ) ions are 10.035 A for 1,8.750 A for 2,10.035 A for 3,9.019 A for 4 and 9.679 A for 5. The magnetic properties of 1-5 have been investigated, displaying weak out-of-phase AC signals under a zero-DC field except 5. With an applied DC field of 1200 Oe, the quantum tunnelling of the magnetization was suppressed in 1-5, giving effective energy barrier (△E/kB) with a following order:5 (91.70 K)> 4 (87.31 K)> 1 (82.93 K)> 2 (55.36 K)> 3 (38.66 K). Interestingly, for frequency dependence of the out-of-phase (χ") of the AC susceptibility of 2, two slow relaxation of the magnetization processes were observed under the applied magnetic field of 1200 Oe, corresponding to the fast relaxation phase (FR) and slow relaxation phase (SR), respectively. The structure-property relationship of some Dy (Ⅲ) based SIMs with SAP configuration was further discussed.2. Two groups of mononuclear SMMs with square-antiprismatic (SAP) N2O6 coordination environment of Dy (Ⅲ) ion, formulated as [Dy(Phen)(tfmb)3] (6) and [Dy(Phen)(tfmb)3]-0.5(1,4-dioxane) (7) as well as Dy(bpy)(tfmb)3] (8) and [Dy(bpy)(tfmb)3]0.5C4H8O2 (9) were obtained, therein, complexes 6 and 8 were transformed to 7 and 9 in 1,4-dioxane through the process of dissolution and precipitation, respectively. Structural analysis shows different configurations of 7(D2a) and 8(D4d). Complex 9 is more closer to the ideal D4d symmetry than 1. Additionally, the different types of weak interactions π-π stacking and hydrogen bonds exist in 6-9. Magnetic studies indicate that complexes 7 and 9 exhibit more high barrier heights (AE/ks) than complexes 6 and 8, respectively, revealing that the subtle structural changes associated with guest solvent result in drastic different effective relaxation barriers.3. Three mononuclear Dysprosium (Ⅲ) complexes, [Hthyl3N][Dy(tffb)4] (10, Hthyl3N= triethylamine) [Butyl4N][Dy(tfnb)4] (11, Butyl4NBr=Tetra-n-butylammonium bromide) and [Hthyl3N][Dy(dbma)4] (12) were synthesized using three kinds of β-diketonate ligands and counter cations. The magnetic studies show that these complexes exhibits the field induced mononuclear SMMs behaviors. We discussed structure-property relationship based on the different counter cations.4. We synthesized two mononuclear Er (Ⅲ) complexes, [Er(Phen)(tfmb)3] (13) and [Er(Phen)(tfnb)3] (14). Both complexes have similar square anti-prismatic coordination geometries around the lanthanide but show distinct magnetic properties.5. A 2D oxalate-bridged dysprosium (Ⅲ) layer was obtained, formula as [Dy(C2O4)1.5(H2O)3]n·2nH2O (15), in which the nine-coordinated Dy (Ⅲ) ions reside in a slightly distorted tricapped trigonal prism. Dy (Ⅲ) ions are connected by double bridging carboxylate groups (double μ2-κO, O) to form a 2D layer, consisting of puckered six-membered rings [Dy(C2O4)]6. Magnetic studies revealed that two slow relaxation of the magnetization processes occurred in 15 under an applied magnetic field of 700 Oe, with energy barriers (△E/kB) of 3.8 and 10.7 K and pre-exponential factors (τ0) of 4.3 × 10-2 and 4.39×-6 s for the fast relaxation phase (FR) and slow relaxation phase (SR), respectively. It is significant to ensure the possibility of synthesizing and tuning the properties of the single-ion magnetic behavior of Dy (Ⅲ) ion in Dy-MOFs in an easy manner. A Dy2 single-molecule magnet, namely [Dy2(H3L)2(PhCOO)4]·4H2O (16), was obtained from the reaction of Dy(PhCOO)3 with 1,5-Bis(2-hydroxy-3-methoxybenzylidene)carbonohydrazide (H4L). Each Dy(Ⅲ) ion is located in the chelating pocket [DyOsN] with a tricapped trigonal prism configuration. The Dy (Ⅲ) centers are bridged by the benzoate anions with μ2:η1,η2 coordination mode and the phenol-O- groups in the form of μ1:η2, respectively. The structure-property relationship of some selected Dy2 paradigmatic compounds was further discussed.更多还原