一种钡金属有机框架材料的合成及其晶体结构和发光性能的研究

金属有机框架(MOFs)因其独特的结构和在晶体工程与材料科学领域中的潜在应用而成为研究热点。目前,大多数MOFs都以过渡金属为中心,而具有特殊构型的第Ⅱ主族金属(碱土金属)受到的关注则相对较少。本文采用溶剂热法,以异烟酸氮氧化物(HINO)为有机配体,与二水合氯化钡(BaCl₂·2H₂O)金属盐合成了一种新型的三维Ba(Ⅱ)-MOF材料Ba(INO)₂]_n。通过单晶X射线衍射、X射线粉末衍射、红外光谱、元素分析、热重分析、荧光光谱等测试对该Ba-MOF进行了结构和性能表征。单晶X射线衍射结果表明:Ba(INO)₂]_n为单斜晶系,Cc空间群,晶胞参数为a=1.636 14(7) nm,b=1.126 35(4) nm,c=0.742 40(3) nm,中心离子Ba(Ⅱ)为高配位数的九配位变形三帽三角棱柱体几何构型。Ba(INO)₂]_n结构中的Ba—O一维链由B型INO配体连接形成二维平面层结构,再由A型INO配体沿着4个方向延伸连接形成三维框架。然而有趣的是,当Ba—O一维链直接由A型INO配体连接时即可形成三维微孔框架,而B型INO配体则进一步撑起该三维框架形成坚实稳定的柱撑结构。Ba(INO)₂]_n表现出良好的热稳定性。此外,固态荧光测试显示,在330 nm紫外光激发下,Ba(INO)₂]_n发出395 nm的蓝光,相比于HINO配体的437 nm最大发射峰,出现了明显的蓝移,这是由INO配体与Ba(Ⅱ)金属离子之间的电荷转移导致的。

Synthesis of a Barium Metal-Organic Framework and Its Crystal Structure and Fluorescence Property

Metal-organic frameworks (MOFs) have become a hotspot because of their unique structures and potential applications in the field of crystal engineering and material science. At present, most metal centers of MOFs are transition metals, while the group Ⅱ metals (alkaline earth metals) with special configurations have obtained relatively less attention. In this work, a novel three-dimensional (3D) Ba(Ⅱ)-MOF, Ba(INO)₂]_n was synthesized by solvothermal method, with isonicotinic acid N-oxide (HINO) as organic ligand and barium chloride dihydrate (BaCl₂·2H₂O) as metal salt. The structure and properties of this Ba-MOF were characterized by single crystal X-ray diffraction, X-ray powder diffraction, infrared spectroscopy, elemental analysis, thermogravimetric analysis and fluorescence spectroscopy. Single crystal X-ray diffraction results show that Ba(INO)₂]_n crystallizes in the monoclinic Cc space group, and the unit cell parameters a=1.636 14 (7) nm, b=1.126 35 (4) nm, c=0.742 40 (3) nm. The Ba(Ⅱ) center is nine-coordinated distorted three cap triangular prism geometry. The Ba—O one-dimensional (1D) chains in Ba(INO)₂]_n are connected by type-B INO ligands to form a two-dimensional (2D) layer, and then extended by type-A INO ligands along four directions to form a 3D framework. However, interestingly, when the Ba—O 1D chains are directly connected by type-A INO ligands, a 3D microporous framework can be formed, while type-B INO ligands further support the 3D framework to form a solid and stable pillared structure. Ba(INO)₂]_n shows good thermal stability. In addition, the solid-state fluorescence test shows that,Ba(INO)₂]_n exhibits a maximum emission peak at 395 nm under the excitation of 330 nm ultraviolet light. It shows an obvious blue shift compared to the 437 nm maximum emission peak of HINO ligand, which is caused by the electronic transition between INO ligand and Ba(Ⅱ) metal center.