Stannous fluoride (SnF₂) is an effective antimicrobial agent and fluoride carrier to dental enamel. However, stannous complexes are known to readily oxidize in presence of O₂ and interact with a variety of ligands such as organic and inorganic compounds commonly present in toothpaste. Therefore, the stability of stannous species inside toothpaste remains an open question. Here we probe the speciation of Sn in solutions of known composition and in commercial toothpaste using Sn K-edge X-ray absorption spectroscopy. We show that the oxidation state of Sn and its chemical nature depends on both paste composition and time of opening, with Sn ultimately oxidizing into amorphous Sn(IV) hydroxide, Sn(OH)₄. These results highlight the effect of paste composition and utilization on the speciation of active ingredients such as SnF₂, and contribute to a rational design of toothpaste formulations that enhances the stability of stannous agents.

Under the oxidizing conditions produced by n-TiO₂ and irradiation, n-Ag₂S is unstable and provokes significant microbial stress.

The identity and structure of tin(II)-fluoride complexes formed in aqueous solutions is determined by combining X-ray absorption spectroscopy, thermodynamic modeling and quantum mechanical calculations. Spectroscopic measurements confirm the presence of 3 stannous fluoride complexes, SnF⁺, SnF⁰ ₂ and SnF₃ ⁻, with mean Sn–F bond distances that increase linearly, from 1.98 to about 2.04 Å, as a function of the coordination number. Computational ab initio calculations indicate that the stannous fluoride complexes form localized σ_s–p bonds, with the stereochemically active lone pair of the Sn(II) atom distorting the geometry of the complexes. In addition, the SnF₃ ⁻ complex exhibits loosely coordinated water, which is removed upon addition of glycerol to lower the solvent activity. Our results provide spectroscopic confirmation of the stannous fluoride complexes proposed in the literature, and explain why glycerol additions stabilize solutions of Sn(II) against oxidation.