Structure of Hydrated and Sulfated Stannic Acid: Quantum-Chemical Modeling

Various H2SnO3 complexes and their hydrated and sulfated derivatives have been studied by the quantum-chemical method within the cluster approximation with the ωB97XD functional and the LanL2DZ(Sn) and 6-31G**(O,S,H) basis sets, as well as considering periodic boundary conditions with the PBE functional and the projector-augmented plane wave (PAW) basis set. It was found that among the hydrated forms, the smallest clusters with features of the SnO2 crystal (two- and threefold coordinated oxygen atoms and five- and sixfold coordinated tin atoms) are (H2SnO3)6 clusters with the circumscribed sphere diameter d ~ 10 Å. Their association (in the form of globules (d ~ 20 Å), chains, films) due to hydrogen bonds with each other and with water molecules is energetically favorable. It is also possible that they aggregate through covalent Sn–O–Sn and Sn–OH–Sn bonds to form various larger nanoparticles, for example, (H2SnO3)12. Interestingly, some of them are hollow structures. Sulfuric acid molecules adsorbed on the surface of (SnO2)n(H2O)m clusters are bound to surface Sn atoms by $${\text{SO}}_{4}^{{2 - }}$$ anions, and the protons that are split off in the process complete the conductivity channels, forming H3O+ and $${{{\text{H}}}_{{\text{5}}}}{\text{O}}_{2}^{ + }$$ cations in them in addition to OH– anions and water.