Role of Anion–π Interactions in the Supramolecular Assembly of Salts Containing Asymmetrical Bis(pyridyl) Cations

Abstract

Self-assembly of three flexible bis(pyridyl) molecules with different inorganic acids (HPF6, HClO4, and HNO3) leads to the formation of eight salts, which exhibit diverse architectures involving hydrogen bonding and anion–π interactions. The three types of inorganic anions in these salts formed anion–π interactions with HM+ and H2M2+ except for 2, in which the six F atoms were involved in hydrogen bonds. Anion–π interactions produced diverse motifs of one (anion)-to-one (cation) in 1, 3, 4, and 6, two (anion)-to-one (cation) in 5 and 7, and (4,4) layer in 8. Hydrogen bonds resulted in interesting supramolecular architectures, such as right- and left-handed helical chains in 3, 2-fold interpenetrating networks in 5, and 3-fold interpenetrating networks in 8. Structural analyses indicated that the conformations of the three flexible asymmetrical bis(pyridyl) molecules and the non-covalent bonding interactions, such as hydrogen bonds and anion···π interactions, play crucial roles in the final architectures of these salts. Thermogravimetric analyses indicated that the thermal stability of the eight salts decreased in the order of perchlorates, hexafluorophosphates, and nitrates. The emission intensity of the perchlorates is much stronger than that of the hexafluorophosphates, nitrates, and their corresponding organic molecules in the solid state at room temperature.