Abstract:
Interaction of 2‐, 3‐, 4‐carboxyethylpyridines (L1, L2, L3) with fluorosilicic acid results
in the corresponding bis(pyridinium) hexafluorosilicates I–III, characterized by
elemental analysis, IR, 1H, 19F nuclear magnetic resonance (NMR), and mass
spectrometry, solubility data, and X‐ray crystallography. Crystallographic data: Fdd2,
Z=8, a = 28.610(2) Å, b = 18.8378(14) Å, c = 7.3236(5) Å (I); P‐1, Z=1, a = 6.2712(4) Å,
b = 7.1706(5) Å, c = 10.9721(7) Å, α = 102.514(6)°, β=97.037(5)°, γ=93.640(6)° (II);
P21/c, Z=2, a = 10.0345(6) Å, b = 9.8734(5) Å, c = 9.4704(6) Å, β = 94.347(6)° (III). The
dominant intermolecular contacts from the Hirshfeld surface analysis are H…F/F…H,
H…H, and H…O/O…H with percentages of 33.3%–34.5%, 26.4%–30.0%, and
16.0%–21.8%. The infrared spectra for I–III exhibit stretching vibrations ν(N+H) at
3300–3050 cm–1; stretching and deformation vibrations ν(SiF) and δ(SiF2) for [SiF6]2–
anions are registered near 740 cm–1 and in the range of 480–440 cm–1. In the 19F
NMR spectra of aqueous solutions of I–III, strong singlet signals of the [SiF6]2– anion
were registered at δ(F) = −133.35 ppm (I), –131.43 ppm (II), –129.02 ppm (III) with two
satellites due to the spin‐spin interaction 29Si–19F (J(29Si–19F) = 107.5 Hz (II), 107.6Hz
(III)). I–III reveal high solubility in water and dimethyl sulfoxide and very poor solubility
in methanol and ethanol. All compounds demonstrate noticeable anticaries activity
and absence of hepatotoxic effects, and bis(3‐carboxyethylpyridinium) hexafluorosilicate
II displays the highest caries‐preventive efficacy, which significantly exceeds
values for the reference preparations, NaF and (NH4)2[SiF6].
