As a part of our systematic investigations of the macrocycles complexation with the fluorosilicic acid (FSA) [1] we have obtained the crystalline products of interaction in the system H2SiF6 – Н2О – L, where L – 12-membered 2,3,5,6,8,9-hexahydro-1,4,7,10-benzotetraoxacyclododecin-12-amine (L1) and monoaza-12-crown-4 (L2). The structures of these new compounds with the compositions (L1H)2SiF6·2H2O (I) and (L2H)[SiF5(H2O)]·H2O (II) were determined by X-ray analysis. The ionic structure I is composed of centrosymmetric SiF6 2– anions (Si–F 1.6588(15) – 1.6719(11) Å), Nprotonated cations L1H+, and two water molecules, which are bound by a system of H-bonds of NH···F, NH···O and OH···F types (fig. a). The SiF6 2– anions and water molecules are assembled into negative layers via OH···F hydrogen bonds (fig. b). No interactions were registered between Oatoms of crown and H-donor fragments (H2O, NH3 +-groups of a symmetry-related cation), and thus I is not a “host-guest” (H-G) complex, but a simple arylammonium hexafluorosilicate. The structure II demonstrated a new and quite rare example of stabilization of the complex anion [SiF5(H2O)]–, the labile product of hydrolytic transformations of SiF6 2– anion in the H-G complex. The components of II, i.e., [SiF5(H2O)]–, L2H+, and water molecules are linked by a system of H-bonds, NH···F, NH···O, OH···F, OH···O (fig. c). In a way similar to I, in II the [SiF5(H2O)]– anions and water molecules form negative layers via OH···F and OH···O interactions (fig. d).figureIn the [SiF5(H2O)]– anion Si–F distances are 1.6424(12) – 1.6979(11) Å, Si–O – 1.8416(15) Å. The shortest Si–F bond (1.6424(12) Å) corresponds to F(2) atom which is not involved in H-bonds. For comparison, the average values of Si–F distances in [SiF5(H2O)]– anion of H-G compounds (L3H·H2O)[SiF5(H2O)]·H2O (L3 – monoaza-18-crown-6) and (L4H2)[SiF5(H2O)]2 (L4 – diaza-18crown-6) are 1.663 and 1.880 Å correspondingly [2]. The physicochemical characteristics of I and II will be discussed.