Experimental and theoretical study of the IR spectrum of [(CH sub(2OH)) sub(3)CNH sub(3]) sub(2)SiF sub(6 crystal)

• Published in: Vibrational spectroscopy Vol. 55; no. 2; pp. 160 - 171
• Main Authors: Podsiadla, D, Czupinski, O, Rospenk, M, Czapla, Z
• Format: Journal Article
• Language: English
• Published: 01.03.2011
• Subjects: Bands; Centre of gravity; Crystals; Density functional theory; Infrared radiation; Mathematical analysis; Phase transformations; Spectroscopy; Vibration
• ISSN: 0924-2031
• DOI: 10.1016/j.vibspec.2010.11.002

[(CH sub(2OH)) sub(3)CNH sub(3]) sub(2)SiF sub(6, (tris(hydroxymethyl)aminomethane)) sub(2)SiF sub(6 crystal, abbreviated as (TRIS)) sub(2)SiF sub(6 crystal, exhibits a solid-solid phase transition (PT) at 182 K. The phase transition is connected with reorientational motion of SiF) sub(6)[super]2- and -CH sub(2OH groups. The vibrational infrared spectra of powdered (TRIS)) sub(2)SiF sub(6 crystal in Nujol and Fluorolube mulls were studied in the wide range of temperatures, from 320 K to 133 K. A wide region of internal vibrations of the TRIS[super]+ and SiF) sub(6)[super]2- ions was investigated. Temperature changes of wavenumber, width, centre of gravity, and intensity of bands were analyzed to clarify the molecular mechanism of the phase transitions. Theoretical calculations were made based on density functional theory (DFT). The calculated normal vibrational modes of the molecules, their frequencies and intensities were compared with those obtained from experimental data.