Where Fluoride\nIs Present, Hexafluorosilicate Might\nBe Encountered: Supramolecular Binding of the SiF<sub>6</sub><sup>2–</sup> Anion by Nanojars

While the fact that HF etches glass is rather common\nchemical knowledge,\nthe reaction of fluoride ions in an organic solvent with glassware\nunder alkaline conditions has not yet been documented. It becomes\napparent that, in general, whenever any fluorine-containing material\nis handled in silicon-based glassware, the possible presence of SiF<sub>6</sub><sup>2–</sup> should be considered regardless of the\npH of the reaction medium. Subsequent to the initial, inadvertent\nsynthesis by the reaction of CuF<sub>2</sub> with laboratory glassware,\nhexafluorosilicate-entrapping supramolecular assemblies (nanojars)\nof the formula [SiF<sub>6</sub>⊂{<i>cis</i>-Cu<sup>II</sup>(μ–OH)(μ-pz)}<i><sub>n</sub></i>]<sup>2–</sup> (<b>Cu</b><i><sub><b>n</b></sub></i><b>SiF</b><sub><b>6</b></sub>; <i>n</i> = 28, 30, 32, 34) were rationally prepared by the reaction\nof Cu<sup>2+</sup> with pyrazole (Hpz) in the presence of a base and\nSiF<sub>6</sub><sup>2–</sup> ions or by combining <b>Cu</b><i><sub><b>n</b></sub></i><b>CO</b><sub><b>3</b></sub> with H<sub>2</sub>SiF<sub>6</sub> or HF. This work\ndemonstrates that nanojars are excellent anion-binding agents not\nonly for trigonal planar/pyramidal or tetrahedral anions but also\nfor larger, octahedral anions, which are bound exclusively by charge-assisted\nhydrogen bonds. The SiF<sub>6</sub><sup>2–</sup> anion guest\nis preferentially bound by a larger Cu<sub>32</sub> host, whereas\nCO<sub>3</sub><sup>2–</sup> favors a smaller Cu<sub>27</sub> nanojar. The <b>Cu</b><i><sub><b>n</b></sub></i><b>SiF</b><sub><b>6</b></sub> mixture was characterized\nby electrospray ionization mass spectrometry as well as variable-temperature,\nparamagnetic <sup>1</sup>H and <sup>19</sup>F NMR spectroscopy in\nsolution, complemented by single-crystal X-ray diffraction studies\nin the solid state, which reveal the unprecedented structure of a\nCu<sub>8+14+10</sub> nanojar (where Cu<sub>8</sub>, Cu<sub>10</sub>, and Cu<sub>14</sub> are the component Cu<sub><i>x</i></sub> metallamacrocycles of the Cu<sub>32</sub> nanojar).