物理化学学报 >> 2020, Vol. 36 >> Issue (9): 1912007.doi: 10.3866/PKU.WHXB201912007

所属专题： 精准纳米合成

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稀土-钛氧簇合物EuTi6，EuTi7和La2Ti14的可控合成

杨亚梅, 伦会洁, 龙腊生, 孔祥建(), 郑兰荪   

  • 收稿日期:2019-12-02 录用日期:2020-01-08 发布日期:2020-02-13
  • 通讯作者: 孔祥建 E-mail:xjkong@xmu.edu.cn
  • 基金资助:
    国家自然科学基金(21871224);国家自然科学基金(21673184);国家自然科学基金(21431005);国家自然科学基金(21721001)

Controlled Synthesis of Lanthanide-titanium Oxo Clusters EuTi6, EuTi7 and La2Ti14

Yamei Yang, Huijie Lun, Lasheng Long, Xiangjian Kong(), Lansun Zheng   

  • Received:2019-12-02 Accepted:2020-01-08 Published:2020-02-13
  • Contact: Xiangjian Kong E-mail:xjkong@xmu.edu.cn
  • Supported by:
    the National Natural Science Foundation of China(21871224);the National Natural Science Foundation of China(21673184);the National Natural Science Foundation of China(21431005);the National Natural Science Foundation of China(21721001)

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摘要：

相比于纳米材料，原子精度的金属簇合物具有精确的表面结构和晶体结构，更有利于在原子水平上去理解化学反应的活性与结构的关系。作为团簇的一个有趣的分支，异金属的稀土-钛氧簇合物因其有趣的化学性质引起了人们的广泛关注。但是稀土-钛氧簇合物的精准合成是目前的重要挑战，这阻碍了其性能的进一步研究。因为螯合配体可以降低Ti4+的水解速度，因此选择合适的螯合配体是制备稀土钛氧团簇的有效方法。最近，我们以螯合作用较强的3, 5-二叔丁基水杨酸(H2dtbsa)为配体，稀土盐和Ti(OiPr)4为原料，通过溶剂热法成功合成了四个新的稀土-钛氧簇合物[EuTi6(μ3-O)3(OC2H5)8(dtbsa)6(Hdtbsa)]·(C2H5OH) (1)，[EuTi7(μ3-O)3(μ2-OH)2(OiPr)9(dtbsa)6(Hdtbsa)Cl]·(HOiPr)3 (2)，[EuTi7(μ3-O)3(μ2-OH)2(OiPr)8(dtbsa)7(Hdtbsa)]·(HOiPr)2 (3)和[LaTi7(μ3-O)3(μ2-OH)2(OC2H5)8(dtbsa)7(Hdtbsa)]2·(C2H5OH)4 (4)。单晶分析表明，七核化合物1内核EuTi6具有三角棱柱的结构，其中Eu3+位于六个Ti4+离子形成的棱柱中心。八核化合物2和3的金属内核结构可以看作是化合物1中三棱柱的一侧连接一个Ti4+。化合物4中，Ln2Ti14的金属骨架可看作是EuTi7的二聚体。紫外-可见漫反射光谱估算的带隙值表明，簇合物1、2和3的禁带宽度值分别为2.35、2.07和2.16 eV，明显小于锐钛矿的禁带宽度值。光电响应测试发现这三种簇合物具有明显的光电响应，而且簇合物1和2的电荷分离效应好于簇合物3。为了探索这类簇合物在光催化方面的应用，我们做了在甲醇水溶液中的光催化(300–800 nm)分解水产氢实验。簇合物1、2和3的产氢率分别为112、106和87 μmol·h-1·g-1，高于商用P25。粉末X射线衍射(PXRD)和热重分析(TGA)证明了簇合物的光热稳定性。本文不但提供了一种制备稀土钛氧簇合物的螯合配体策略，而且还表明稀土钛氧簇合物具有较低的带隙和光驱动的催化活性。

关键词: 稀土-钛氧簇合物, 精确结构, 溶剂热法, 产氢, 光解水

Abstract:

As opposed to nanoparticles, atomically precise metal clusters possess a well-defined surface and crystal structure, which aids in understanding the relationship between the structure and chemical reactivity at the atomic level. As an interesting subgroup of metal cluster compounds, heterometallic lanthanide-titanium oxo clusters (LnTOCs) have attracted extensive attention due to their interesting chemical properties. However, the controlled precise synthesis of LnTOCs remains a great challenge because of the intense hydrolysis of Ti4+ ions and the competitive coordination of Ln3+ ions. Owing to this synthetic difficulty, high-nuclearity LnTOCs are very rare, which obstructs further studies on their properties. Choosing the appropriate chelating ligands should be an effective strategy to synthesize LnTOCs because chelating ligands can reduce the degree of hydrolysis of Ti4+ ions. Herein, four new LnTOCs, formulated as [EuTi6(μ3-O)3(OC2H5)8(dtbsa)6(Hdtbsa)]·(C2H5OH) (1), [EuTi7(μ3-O)3(μ2-OH)2(OiPr)9(dtbsa)6(Hdtbsa)Cl]·(HOiPr)3 (2), [EuTi7(μ3-O)3(μ2-OH)2(OiPr)8(dtbsa)7(Hdtbsa)]·(HOiPr)3 (3), and [LaTi7(μ3-O)3(μ2-OH)2(OC2H5)8(dtbsa)7(Hdtbsa)]2·(C2H5OH)4 (4), were prepared by a solvothermal method via the reaction of 3, 5-di-tert-butylsalicylic acid (H2dtbsa), rare-earth salts, and Ti(OiPr)4. Single-crystal analysis showed that the heptanuclear compound 1 contains a EuTi6 metal core featuring a trigonal prismatic structure, wherein Eu3+ is located at the center of the prism formed by six Ti4+ ions. The metal core structure of octanuclear compounds 2 and 3 can be viewed as the EuTi6 unit in 1 connected to another Ti4+ on one side of the triangular prism. The metal framework of Ln2Ti14 in 4 can be regarded as a dimer of EuTi7 in 2. UV-Vis diffuse reflectance spectra revealed that the band gaps of 1, 2, and 3 (2.35, 2.07, and 2.16 eV, respectively) are significantly smaller than that of anatase (3.2 eV). The results of photoelectric tests indicated that the three clusters show an obvious photoelectric response, and the charge separation efficiency of 1 and 2 was better than that of 3. In order to explore the applications of these compounds to photocatalysis, H2 production by light-driven water splitting under irradiation by a 300 W Xe lamp (300–800 nm) in an aqueous methanol solution (20 mL, 10%) was attempted. The H2 production rates for 1, 2, and 3 were 112, 106, and 87 μmol∙h-1∙g-1, respectively, which were higher than that obtained with the commercial P25. Powder X-ray diffraction (PXRD) spectra and thermogravimetry (TGA) profiles confirmed the optical and thermal stability of the three clusters. This work not only provides a chelating ligand strategy for the synthesis of LnTOCs but also reveals their light-driven photocatalytic activity stemming from the small band-gap.

Key words: Lanthanide-titanium oxo cluster, Well-defined structure, Solvothermal method, H2 production, Water splitting