Insight into systematic formation of hexafluorosilicate during crystallization via self-assembly in a glass vessel

Abstract

Formation of the unexpected hexafluorosilicate (SiF62−) anion during crystallization via self-assembly in glassware is scrutinized. Self-assembly of M(BF4)2 (M2+ = Cu2+ and Zn2+) with tridentate N-donors (L) in a mixture solvent including methanol in a glass vessel gives rise to an SiF62−-encapsulated Cu3L4 double-decker cage and a Zn2L4 cage, respectively. Induced reaction of CuX2 (X− = PF6− and SbF6−) instead of Cu(BF4)2, with the tridentate ligands, produces the same species. The formation time of SiF62− is in the order of anions BF4− < PF6− < SbF6− under the given reaction conditions. The SiF62− anion, acting as a cage template or cage-to-cage bridge, seems to be formed from the reaction of polyatomic anions containing fluoride with the SiO2 of the surface of the glass vessel.