Crystal Structures of Solids Produced by Reacting ε-Caprolactam with Hydrofluorosilicic Acid and Copper(II) Hexafluorosilicate

Abstract

New compounds (HOOC(CH₂)₅NH₃)₂SiF₆ (1) and [Cu(Cpl)₂(H₂O)₂SiF₆]·2Cpl (2), where Cpl = ε-caprolactam ε-C₆H₁₁NO and (HOOC(CH₂)₅NH₃)⁺ is the 5-carboxypentylammonium ion, were prepared from aqueous solutions and characterized by chemical analysis, IR spectroscopy, and single-crystal X-ray diffraction. In the structure of compound 1, the coordination surrounding of a Si atom is a nearly regular octahedron. The crystals of 1 are triclinic, space group P\(\overline 1 \). The caprolactam is hydrated and protonated upon crystallization. Hydrogen bonds F…Н–N between \({\text{SiF}}_{6}^{{2 - }}\) anions and organic cations and acidic hydrogen bonds between the carboxy groups of cations were found to exist in the structure of 1. Compound 2 crystallizes in triclinic crystal system, space group P\(\overline 1 \), and has a chain-polymeric structure. The coordination polyhedra of the two unique copper ions are tetragonally distorted octahedra formed by the O atoms of two Cpl molecules and two F atoms of the hexafluorosilicate ions, which perform as bridges between nearest neighboring cations. The coordination surrounding around a Si atom is a slightly distorted octahedron. Hydrogen bonds between the H atoms of coordinated water molecules and the O atoms of uncoordinated Cpl molecules exist in the structure. The hexafluorosilicate ions in the structures of 1 and 2 have identical geometries.