Structural, Vibrational, Thermal, Phase Transitions, and Properties Review of Alkylammonium, Alkylenediammonium, and Aminoacid Hexafluorosilicate Salts

The present paper aims to review and discuss structural, thermal, phase transitions, solubility, catalytical, anticaries and toxicity properties of alkylammonium [R4 – nNHn]2SiF6, alkylenediammonium NH3(CH2)nNH3SiF6, and amino acid hexafluorosilicate salts, which have been previously published. Structural comparative analyses are made on the crystal structures, which have been determined for these compounds. The effect of hydrogen bonding on the Si···F elongation bonds is reviewed in terms of solid-state relationship. For the solution event, the hydrogen bonds are discussed in relation to the hexafluorosilicate compounds solubility. The vibrational and thermal properties of the hexafluorosilicates are reviewed and discussed, which lead us to highlight as well as the mechanisms and the characters of the phase transitions undergone by these compounds. The NH3(CH2)nNH3SiF6 (n = 4, 6) and (N2H5)2SiF6 salts are found to be highly efficient novel catalysts in the synthetic protocols for organic compounds such as benzimidazoles, benzothiazole and benzoxazole, 3,4-dihydropyrimidin-2-ones/thiones and quinoxalines derivatives, which is considered as a novel tendency in the hexafluorosilicate researchs, particularly in the green chemistry field. The toxicological and anticaries properties of some hexafluorosilicate compounds are reviewed. Besides, the identification and quantification methods of new potential medical substances based on these salts are discussed.