Preparation, structure and properties of pyridinium/bipyridinium hexafluorosilicates

• New pyridinium/bipyridinium hexafluorosilicates as potential caries-protected agents.
• Increase of H-donor numbers as a factor influencing the solubility of salts.
• Identification of neutral chelate cis-[SiF4(2,2′-Bipy)] from acidic aqueous-organic medium.

Pyridinium hexafluorosilicates with the compositions (LH)2[SiF6] (where L = 2,6-bis(hydroxymethyl)pyridine (I), 4,5-bis(hydroxymethyl)-2-methylpyridine-3-ol (II)), monohydrate (LH)2[SiF6]·H2O (L = 2-bromo-6-methylpyridine (III)) and (LH2)[SiF6] (L = 4,4′-bipyridine (IV), 2,2′-bipyridine (V)) were separated as crystalline products of interaction of fluorosilicic acid with different pyridines. All compounds were characterized by elemental analysis, IR, NMR 19F and mass-spectrometry, solubility data, and X-ray crystallography. The structural study revealed the details of the anion binding and solid state supramolecular architectures provided by the combination of the plethora of intermolecular interactions including strong charge assisted and conventional hydrogen bonds of NH⋯F, OH⋯F types along with O⋯Br contacts and π–π interactions. The relationship between the salts structure and physico-chemical properties is discussed.

Five new pyridinium/bipyridinium hexafluorosilicates were prepared and studied as potential caries-protected agents.Figure optionsDownload as PowerPoint slide