AUTHOR=Li Jie , Shang Shuxia , Lin Zhengguo , Yao Zishuo , Zhen Ni , Li Zhen , Chi Yingnan , Hu Changwen 

TITLE=Assembly of Lanthanide-Containing Tungstotellurates(VI): Syntheses, Structures, and Catalytic Properties

JOURNAL=Frontiers in Chemistry

VOLUME=8

YEAR=2020

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2020.598961

DOI=10.3389/fchem.2020.598961

ISSN=2296-2646

ABSTRACT=<p>Lanthanide (Ln)-containing polyoxometalates (POMs) have attracted particular attention owing to their structural diversity and potential applications in luminescence, magnetism, and catalysis. Herein three types of Ln-containing tungstotellurates(VI) (Ln = Dy<sup>3+</sup>, Ho<sup>3+</sup>, Er<sup>3+</sup>, Tm<sup>3+</sup>, Yb<sup>3+</sup>, and Lu<sup>3+</sup>), dimeric (DMAH)<sub><italic>n</italic></sub>[H<sub>22−<italic>n</italic></sub>{Ln(H<sub>2</sub>O)<sub>3</sub>[TeW<sub>17</sub>O<sub>61</sub>]}<sub>2</sub>]<sup>·</sup>mH<sub>2</sub>O (abbreviated as {Ln<sub>2</sub>Te<sub>2</sub>W<sub>34</sub>}; DMAH<sup>+</sup> = dimethylammonium), mono-substituted (DMAH)<sub>7</sub>Na<sub>2</sub>{H<sub>2</sub>Ln(H<sub>2</sub>O)<sub>4</sub>[TeW<sub>17</sub>O<sub>61</sub>]}<sup>·</sup>mH<sub>2</sub>O (abbreviated as {LnTeW<sub>17</sub>}), and three-dimensional (3D) inorganic frameworks (DMAH)<sub><italic>n</italic></sub>{H<sub>3−<italic>n</italic></sub>Ln(H<sub>2</sub>O)<sub>4</sub>[TeW<sub>6</sub>O<sub>24</sub>]}<sup>·</sup>mH<sub>2</sub>O (abbreviated as {LnTeW<sub>6</sub>}), have been synthesized by using simple metal salts and characterized by single-crystal X-ray diffraction and other routine techniques. Interestingly, the assembly of these POMs is pH dependent. Using the same starting materials, {Ln<sub>2</sub>Te<sub>2</sub>W<sub>34</sub>} were obtained at pH 1.7, where two Dawson-like monovacant [TeW<sub>17</sub>O<sub>61</sub>]<sup>14−</sup> are linked by two Ln<sup>3+</sup> ions; mono-substituted Dawson-like {LnTeW<sub>17</sub>} were isolated at pH 1.9, and 3D inorganic framework {LnTeW<sub>6</sub>} based on Anderson-type [TeW<sub>6</sub>O<sub>24</sub>]<sup>6−</sup> were formed at pH 2.3. It was also found that the assembly of Ln-containing POMs depends on the type of Ln<sup>3+</sup> ions. The three types of POMs can be prepared by using Ln<sup>3+</sup> ions with a relatively smaller ionic radius, such as Tb<sup>3+</sup>-Lu<sup>3+</sup>, while the use of Ln<sup>3+</sup> ions (La<sup>3+</sup>-Eu<sup>3+</sup>) results in the formation of precipitation or {TeW<sub>18</sub>O<sub>62</sub>} clusters. Furthermore, three {LnTeW<sub>6</sub>} (Ln = Tb<sup>3+</sup>, Er<sup>3+</sup>, Lu<sup>3+</sup>) were used as Lewis acid catalysts for the cyanosilylation of benzaldehydes, and their catalytic activity decreases with the decrease of Ln<sup>3+</sup> ionic radius, giving the order: {TbTeW<sub>6</sub>} &gt; {ErTeW<sub>6</sub>} &gt; {LuTeW<sub>6</sub>}. Notably, {TbTeW<sub>6</sub>} is stable to leaching and can be reused for five cycles without a significant loss of its activity.</p>