Anion-Guided Hierarchical Assembly of Heterometallic Clusters

Anions are important as templates for the construction of many structurally sophisticated and functional supramolecular architectures. Deciphering the specific role of such templates remains a great challenge due to the unique characteristics of anions. Herein, three heterometallic Ce-Ni clusters, namely, [Ce₂₄Ni₃₆<b>L</b>₃₆(<b>μ</b>_<b>4</b>-<b>OAc</b>)₆(OH)₅₂(Cl)₈]Cl₆·110H₂O (<b>Ce</b>_<b>24</b><b>Ni</b>_<b>36</b>, <b>OAc</b> = acetate ion, <b>L</b> = <i>N</i>-methyliminodiacetate), [Ce₁₇Ni₂₇<b>L</b>₂₇(<b>μ</b>_<b>6</b>-<b>C</b>_<b>2</b><b>O</b>_<b>4</b>)₆(OH)₁₅(Cl)₁₆(H₂O)₁₉](ClO₄)₂Cl₆·45H₂O (<b>Ce</b>_<b>17</b><b>Ni</b>_<b>27</b>), and [Ce₂₁Ni₃₀<b>L</b>₃₀(<b>μ</b>_<b>6</b>-<b>C</b>_<b>2</b><b>O</b>_<b>4</b>)₂(<b>μ</b>_<b>4</b>-<b>OAc</b>)(OH)₃₂(Cl)₁₅(H₂O)₁₄](ClO₄)₄Cl₇·55H₂O (<b>Ce</b>_<b>21</b><b>Ni</b>_<b>30</b>), were obtained and structurally characterized; the formation of these cage-like clusters was assisted, respectively, by acetate, oxalate, and a combination of the two as templates. Structural analyses generate key information on the anion-directed hierarchical assembly, starting from a primary building block of {CeNi₃} to two anion-specific secondary building blocks (SBUs)─the tetragonal {Ce₄Ni₈(<b>OAc</b>)} and the pentagonal {Ce₅Ni₉(<b>C</b>_<b>2</b><b>O</b>_<b>4</b>)}. Further assembly steps are guided by these curved SBUs, affording a truncated octahedral <b>Ce</b>_<b>24</b><b>Ni</b>_<b>36</b> and a lantern-like <b>Ce</b>_<b>17</b><b>Ni</b>_<b>27</b>, with acetate and oxalate being the sole template, respectively. The combined use of acetate and oxalate produced <b>Ce</b>_<b>21</b><b>Ni</b>_<b>30</b>, a cluster with an unprecedented structure viewable as a hybrid of a truncated octahedron and a dodecahedron.