物理化学学报

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2,4,6-三甲基苯甲酸与5,5’-二甲基-2,2’-联吡啶构筑的系列镧系超分子配合物的晶体结构、热分解机理和性能

周孟雪1,2, 任宁3, 张建军1,2   

  1. 1 河北师范大学分析测试中心, 石家庄 050024;
    2 河北师范大学化学与材料科学学院, 石家庄 050024;
    3 邯郸学院, 化学化工与材料学院, 河北省杂环化合物重点实验室, 河北 邯郸 056005
  • 收稿日期:2020-04-27 修回日期:2020-05-15 录用日期:2020-05-15 发布日期:2020-05-20
  • 通讯作者: 任宁, 张建军 E-mail:jjzhang6@126.com;ningren9@163.com
  • 基金资助:
    国家自然科学基金(21803016)资助项目

Crystal Structure, Thermal Decomposition Mechanism and Properties of Lanthanide Supramolecular Complexes Based on 2,4,6-Trimethylbenzoic Acid and 5,5’-Dimethyl-2,2’-bipyridine

Mengxue Zhou1,2, Ning Ren3, Jianjun Zhang1,2   

  1. 1 Testing and Analysis Center, Hebei Normal University, Shijiazhuang 050024, P. R. China;
    2 College of Chemistry & Material Science, Hebei Normal University, Shijiazhuang 050024, P. R. China;
    3 College of Chemical Engineering & Material, Hebei Key Laboratory of Heterocyclic Compounds, Handan University, Handan 056005, Hebei Province, P. R. China
  • Received:2020-04-27 Revised:2020-05-15 Accepted:2020-05-15 Published:2020-05-20
  • Supported by:
    The project was supported by the National Natural Science Foundation of China (21803016).

摘要: 利用2,4,6-三甲基苯甲酸和5,5’-二甲基-2,2’-联吡啶配体在溶剂热的条件下成功合成出系列三元稀土超分子配合物[Ln(2,4,6-TMBA)3(5,5’-DM-2,2’-bipy)]2(Ln=Pr 1,Nd 2,Sm 3,Eu 4,Gd 5,Dy 6),并对其进行了单晶X-射线衍射、元素分析、热重分析等一系列表征。研究结果表明配合物1-5同构,中心离子的配位数为9,配合物通过π-π堆积作用形成一维、二维的超分子结构。配合物6具有不同的结构,中心镝离子的配位数为8,分子间通过π-π堆积作用和C-H…O氢键形成一维、二维的超分子结构。利用TG/FTIR技术研究了配合物的热稳定性和热分解机理,荧光光谱表明配合物4可以发射出Eu3+离子的特征荧光,同时对配合物6的磁性进行了初步探究。

关键词: 镧系超分子配合物, 晶体结构, 热分析, 荧光光谱, 2,4,6-三甲基苯甲酸

Abstract: Six ternary lanthanide complexes formulated as [Ln(2,4,6-TMBA)3(5,5’-DM-2,2’-bipy)]2 (Ln = Pr 1, Nd 2, Sm 3, Eu 4, Gd 5, Dy 6; 2,4,6-TMBA = 2,4,6-trimethylbenzoate; 5,5’-DM-2,2'-bipy = 5,5'-dimethyl-2,2'-bipyridine) have been synthesized under solvothermal conditions and characterized by single-crystal X-ray diffraction, elemental analysis, thermogravimetric analysis, etc. The results of crystal diffraction analysis show that complexes 1–6 are binuclear units, crystallizing in the triclinic space group. Complexes 1–5 are isostructural, and each of the central metal ions has a coordination number of 9. The asymmetric unit of complexes 1–5 consists of one Ln3+, one 5,5’-DM-2,2’-bipy ligand, and three 2,4,6-TMBA- moieties with three coordination modes: chelation bidentate, bridging bidentate, and bridging tridentate. The coordination geometry of Ln3+ is distorted monocapped square antiprismatic. The binuclear units of complexes 1–5 form a one-dimensional (1D) supramolecular chain along the c-axis via ππ stacking interactions between the 2,4,6-trimethylbenzoic acid rings. The 1D chains are linked to form a supramolecular two-dimensional (2D) sheet in the bc plane via ππ stacking interactions between the pyridine rings. Although the molecular formulae of complex 6 and complexes 1–5 are similar, the coordination environment of the lanthanide ions is different in the two cases. The asymmetric unit of complex 6 contains a Dy3+ ion coordinated by a bidentate 5,5’-DM-2,2’-bipy and three 2,4,6-TMBA- ligands adopting bidentate and bridging bidentate coordination modes. The Dy3+ metal center has a coordination number of 8, with distorted square antiprismatic molecular geometry. The binuclear molecule of 6 is assembled into a six-nuclear unit by ππ weak staking interactions between two 5,5’-DM-2,2’-bipy ligands; then, adjacent six-nuclear units form a 1D chain via offset ππ interactions between 5,5’-DM-2,2’-bipy ligands on different adjacent units. The adjacent 1D chains are linked by C―H…O hydrogen bonding interactions to form a 2D supramolecular structure. The thermal stability and thermal decomposition mechanism of all the complexes are investigated by the combination of thermogravimetry and infrared spectroscopy (TG/FTIR) techniques under a simulated air atmosphere in the temperature range of 298–973 K at a heating rate of 10 K·min-1. Thermogravimetric studies show that this series of complexes have excellent thermal stability. During the thermal decomposition of the complex, the neutral ligand is lost first, followed by the acid ligand, and finally, the complex is decomposed into rare earth oxides. The three-dimensional infrared results are consistent with the thermogravimetric results. The photoluminescence spectra of complex 4 show the strong characteristic luminescence of Eu3+. The five typical emission peaks at 581, 591, 621, 651, and 701 nm correspond to the 5D07F0, 5D07F1, 5D07F2, 5D07F3, and 5D07F4 electronic transitions of Eu3+, respectively. The emission at 621 nm is due to the electric dipole transition 5D07F2, while that at 591 nm is assigned to the 5D07F1 the magnetic dipole transition. The lifetime (τ) of complex 4 is calculated as 1.15 ms based on the equation τ = (B1τ12 + B2τ22))/(B1τ1 + B2τ2), and the intrinsic quantum yield is calculated to be 45.1%. Further, the magnetic properties of complex 6 in the temperature range of 2–300 K are studied under an applied magnetic field of 1000 Oe.

Key words: Lanthanide supramolecular complexes, Crystal structure,Thermal behavior, Luminescence spectrum, 2,4,6-Trimethylbenzoic acid

MSC2000: 

  • O642