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

Formation of the unexpected hexafluorosilicate (SiF(6)(2−)) anion during crystallization via self-assembly in glassware is scrutinized. Self-assembly of M(BF(4))(2) (M(2+) = Cu(2+) and Zn(2+)) with tridentate N-donors (L) in a mixture solvent including methanol in a glass vessel gives rise to an SiF(6)(2−)-encapsulated Cu(3)L(4) double-decker cage and a Zn(2)L(4) cage, respectively. Induced reaction of CuX(2) (X(−) = PF(6)(−) and SbF(6)(−)) instead of Cu(BF(4))(2), with the tridentate ligands, produces the same species. The formation time of SiF(6)(2−) is in the order of anions BF(4)(−) < PF(6)(−) < SbF(6)(−) under the given reaction conditions. The SiF(6)(2−) 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 SiO(2) of the surface of the glass vessel.