Finding Rules Governing Layered Architectures of Trifluoroborate Potassium Salts in the Solid State

A set of 15 new crystal structures of aryltrifluoroborate potassium salts (ArBF₃^–K⁺), with various substituents at the aromatic ring, is reported. The considered substituents belong to one of three groups: CF₃, halogen atoms (F, Cl, Br, I), and alkoxy functions (OMe, OEt, O^<i>i</i>Pr). All crystals were obtained via solvent evaporation, and the structural features were determined using single-crystal X-ray diffraction methods (including transferred aspherical atom model, TAAM). The resulting layered crystal structures were parametrized, whereas selected ones were additionally characterized computationally (using the periodic DFT approach). The data allowed for formulating basic rules characterizing a given layered structure of the parent phenyltrifluoroborate potassium salt derivative on the basis of the type and location of the aromatic ring substituents. These layered structures can be classified as single or double sheet depending on the mutual arrangement of the potassium cations. The double-sheet type of the ionic layer is formed in the parent compound (PhBF₃^–K⁺) and most of its simple derivatives. This motif is broken into the single-sheet type by the presence of solvent molecules (water or acetone) or alkoxy groups. Another general observation is that the electron-donating <i>ortho</i>-substituents are coordinated to metal centers unless a more energetically favorable interaction can be formed (e.g., Br···I). Among the studied structures, layers interact one with another via various weak intermolecular interactions, i.e., from weak C–H···π contacts, through C–H···O and C–H···F interactions, up to halogen bonds (I···I, Br···I, Br···F). The layered character of the studied crystal structures and a very significant difference in the strength of hydrophobic and hydrophilic interactions are reflected in the platelike crystal morphology and their common tendency to stratify parallel to the layer planes