Where Fluoride Is Present, Hexafluorosilicate Might Be Encountered: Supramolecular Binding of the SiF₆^2– Anion by Nanojars

While the fact that HF etches glass is rather common chemical knowledge, the reaction of fluoride ions in an organic solvent with glassware under alkaline conditions has not yet been documented. It becomes apparent that, in general, whenever any fluorine-containing material is handled in silicon-based glassware, the possible presence of SiF₆ ^2- should be considered regardless of the pH of the reaction medium. Subsequent to the initial, inadvertent synthesis by the reaction of CuF₂ with laboratory glassware, hexafluorosilicate-entrapping supramolecular assemblies (nanojars) of the formula [SiF₆⊂{<i>cis</i>-Cu^II(μ-OH)(μ-pz)} <i>_n</i> ]^2- (<b>Cu</b> <i>_<b>n</b> </i> <b>SiF</b> _<b>6</b> ; <i>n</i> = 28, 30, 32, 34) were rationally prepared by the reaction of Cu²⁺ with pyrazole (Hpz) in the presence of a base and SiF₆ ^2- ions or by combining <b>Cu</b> <i>_<b>n</b> </i> <b>CO</b> _<b>3</b> with H₂SiF₆ or HF. This work demonstrates that nanojars are excellent anion-binding agents not only for trigonal planar/pyramidal or tetrahedral anions but also for larger, octahedral anions, which are bound exclusively by charge-assisted hydrogen bonds. The SiF₆ ^2- anion guest is preferentially bound by a larger Cu₃₂ host, whereas CO₃ ^2- favors a smaller Cu₂₇ nanojar. The <b>Cu</b> <i>_<b>n</b> </i> <b>SiF</b> _<b>6</b> mixture was characterized by electrospray ionization mass spectrometry as well as variable-temperature, paramagnetic ¹H and ¹⁹F NMR spectroscopy in solution, complemented by single-crystal X-ray diffraction studies in the solid state, which reveal the unprecedented structure of a Cu_8+14+10 nanojar (where Cu₈, Cu₁₀, and Cu₁₄ are the component Cu _<i>x</i> metallamacrocycles of the Cu₃₂ nanojar).