Solid state DFT modeling and vibrational characterisation of butylenediammonium and hexylenediammonium hexafluorosilicate, NH3(CH2)nNH3SiF6 (n = 4 and 6)

Experimental and periodic DFT studies of the structural and vibrational (infrared and Raman) properties of two alkylenediammonium hexafluorosilicate compounds, NH3(CH2)4NH3SiF6 (1) and NH3(CH2)6NH3SiF6 (2), have been performed in crystal phase, where three-dimensional NH⋯F hydrogen bonds (HB) network was formed. The analysis of the vibrational spectra was supported by factor group analysis, periodic DFT modeling and spectra calculations of 1 and 2 in solid state using the unit cell parameters obtained from the experiment. The splitting of the degenerated modes of 1 and 2 was explained by site effects on the internal modes of the isolated ions due to symmetry lowering in the crystals. Stronger NH⋯F hydrogen bonding was suggested for 2 in comparison to 1. The effect of the HB interactions on the geometrical and vibrational characteristics of the ions in the complexes studied was examined. It was shown that the frequencies of the stretching SiF modes could be used as characteristic spectroscopic data for estimation of the HB relative strength in the series of alkylenediammonium hexafluorosilicate.