X-Ray, DSC, TGA-dTGA, and Vibrational Studies of the Propylenediammonium Hexafluorosilicate NH3(CH2)3NH3SiF6

Abstract

X-ray characterization, thermal behavior, and vibrational studies have been performed on NH3(CH2)3NH3SiF6, which crystallized in the P21/c (Z = 4) monoclinic system. The V/Z ratio variation (unit cell volume/ motifs number per cell) versus the CH2 groups’ number is discussed for H3N(CH2)nNH3SiF6salts (n = 2, 3, 4, 6). The DSC measurements (heating/cooling) recorded in the 35-245°C temperature domain showed the NH3(CH2)3NH3SiF6 decomposition above 30 °C, which is checked and analyzed by TGA-dTGA techniques. The vibrational spectra interpretation is developed based on theoretical group analyses considering the +NH3(CH2)3NH3+ cations and the SiF62-anions in the C1(4) and Ci(2) symmetry sites, respectively. The SiF62-degenerated modes splitting is explained by the site effect, resulting in symmetry lowering from Oh to Ci in the crystal. The Infrared spectrum analysis at lower N-H and C-H frequencies region showed the presence of medium to strong N-HF hydrogen bonding in the title compound.