Two new “onium” fluorosilicates, the products of interaction of fluorosilicic acid with 12-membered macrocycles: structures and spectroscopic properties

Two novel compounds, (L1H)2[SiF6]·2H2O (1) and (L2H)2[SiF5(H2O)]2·3H2O (2), resulting from the reactions of H2SiF6 with 4′-aminobenzo-12-crown-4 (L1) and monoaza-12-crown-4 (L2), respectively, were studied by X-ray diffraction and characterised by IR and 19F NMR spectroscopic methods. Both complexes have ionic structures due to the proton transfer from the fluorosilicic acid to the primary amine group in L1 and secondary amine group incorporated into the macrocycle L2. The structure of 1 is composed of [SiF6]2− centrosymmetric anions, N-protonated cations (L1H)+, and two water molecules, all components being bound in the layer through a system of NH⋯F, NH⋯O and OH⋯F hydrogen bonds. The [SiF6]2− anions and water molecules are assembled into inorganic negatively-charged layers via OH⋯F hydrogen bonds. The structure of 2 is a rare example of stabilisation of the complex anion [SiF5(H2O)]−, the labile product of hydrolytic transformations of the [SiF6]2− anion in an aqueous solution. The components of 2, i.e., [SiF5(H2O)]−, (L2H)+, and water molecules, are linked by a system of NH⋯F, NH⋯O, OH⋯F, OH⋯O hydrogen bonds. In a way similar to 1, the [SiF5(H2O)]− anions and water molecules in 2 are combined into an inorganic negatively-charged layer through OH⋯F and OH⋯O interactions.