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

Two novel compounds, (L(1)H)(2)SiF(6)] x 2H(2)O (1) and (L(2)H)(2)SiF(5)(H(2)O)](2) x 3H(2)O (2), resulting from the reactions of H(2)SiF(6) with 4'-aminobenzo-12-crown-4 (L(1)) and monoaza-12-crown-4 (L(2)), respectively, were studied by X-ray diffraction and characterised by IR and (19)F NMR spectroscopic methods. Both complexes have ionic structures due to the proton transfer from the fluorosilicic acid to the primary amine group in L(1) and secondary amine group incorporated into the macrocycle L(2). The structure of 1 is composed of SiF(6)](2-) centrosymmetric anions, N-protonated cations (L(1)H)(+), 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 SiF(6)](2-) anions and water molecules are assembled into inorganic negatively-charged layers via OHdot dot dot]F hydrogen bonds. The structure of 2 is a rare example of stabilisation of the complex anion SiF(5)(H(2)O)](-), the labile product of hydrolytic transformations of the SiF(6)](2-) anion in an aqueous solution. The components of 2, i.e., SiF(5)(H(2)O)](-), (L(2)H)(+), and water molecules, are linked by a system of NH...]F, NH...]O, OH...]F, OHdot dot dot]O hydrogen bonds. In a way similar to 1, the SiF(5)(H(2)O)](-) anions and water molecules in 2 are combined into an inorganic negatively-charged layer through OH...]F and OH...]O interactions.