Acta Physico-Chimica Sinica ›› 2020, Vol. 36 ›› Issue (9): 1912007.doi: 10.3866/PKU.WHXB201912007

Special Issue: Precise Nanosynthesis

• Article • Previous Articles     Next Articles

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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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