A 3D Heterometallic Coordination Polymer Constructed by Trimeric {NiDy2} Single-Molecule Magnet Units

The solvothermal reaction of DyCl3·6H2O, Ni­(NO3)2·6H2O, and H4abtc ligands (H4abtc = 3,3′,5,5′-azobenzene-tetracarboxylic acid) in the mixed DMF/H2O solvents (DMF = N,N-dimethylformamide) produced a three-dimensional (3D) NiII–DyIII heterometallic coordination polymer (HCP) formulated as {[NH2(CH3)2]2­[NiDy2­(HCOO)2­(abtc)2]}n (1). In 1, DyIII and NiII ions interconnect through carboxylic O donors of abtc4– ligands to generate a linear trimer “Hourglass”-type {NiDy2} cluster, and the adjacent trinuclear {NiDy2} units are bridged by HCOO– groups to give a 1D “ladder” chain, which is further bridged by abtc4– ligands to form a new topology and named as “zsw3”. Alternating-current magnetic susceptibility results indicate that 1 exhibits frequency-dependent out-of-phase signals with two relaxation processes, which suggests that it shows single-molecule magnet (SMM) behavior and represents the first example by using an SMM cluster as the building block to create a 3D Ni–Ln HCP, to the best of our knowledge. The energy barriers for 1 under a 1000 Oe applied direct current magnetic field are estimated from Arrhenius plots to be 40 and 42 K at higher and lower frequencies, respectively. Additionally, the crystalline structure of 1 could be stable to at least 310 °C, supported by thermogravimetric analyses and in situ variable-temperature powder X-ray diffraction patterns.

以六水合氯化镝（DyCl₃·6H₂O）、六水合硝酸镍（Ni(NO₃)₂·6H₂O）与3,3′,5,5′-偶氮苯四羧酸（H₄abtc）配体为原料，在N,N-二甲基甲酰胺/水（DMF = N,N-二甲基甲酰胺）混合溶剂中通过溶剂热反应，得到分子式为{[NH₂(CH₃)₂]₂[NiDy₂(HCOO)₂(abtc)₂]}ₙ（化合物1）的三维异金属Ni(II)-Dy(III)配位聚合物（HCP）。在化合物1中，Dy³+与Ni²+离子通过abtc⁴-配体的羧酸氧供体相互连接，形成线性三聚“沙漏”型{NiDy₂}簇；相邻三核{NiDy₂}单元经由甲酸根（HCOO⁻）桥联，构筑出一维“梯形”链，该一维链再经由abtc⁴-配体进一步桥联，形成新型拓扑结构并命名为"zsw3"。交流磁化率测试结果显示，化合物1表现出频率依赖性异相信号，且存在两个弛豫过程，表明其具备单分子磁体（single-molecule magnet, SMM）行为；据我们所知，该工作是首例以单分子磁体簇作为结构基元构建三维镍-镧系异金属配位聚合物的案例。在1000 Oe的直流磁场下，通过阿伦尼乌斯（Arrhenius）曲线拟合得到该化合物的弛豫能垒：高频区为40 K，低频区为42 K。此外，热重分析与原位变温粉末X射线衍射图谱证实，化合物1的晶体结构至少可稳定至310 ℃。