Rotational disorder in 2‐piperidyl‐5‐nitro‐6 ‐methylpyridine: structural phase transition and its vibrational characteristics

Abstract

X-ray diffraction (XRD) studies have shown that 2-piperidyl-5-nitro-6-methylpyridine, C 11 H 15 N 3 O 2 , undergoes a structural phase transition at T = 240 K. The room temperature structure is tetragonal, space group I4 1 /a, with the unit-cell dimensions a = 13.993(2) and c = 23.585(5) Å. The pyridine ring takes trans conformation with respect to the piperidine unit. While pyridine is well ordered, the piperidine moiety shows apparent disorder resulting from a libration about the linking N-C bond. The low-temperature phase is monoclinic, space group I2/a. Contraction of the unit-cell volume by 2.3% at 170 K enables the C-H· · ·O linkage between the molecules of the neighbouring stacks. As result, the asymmetric unit becomes bi-molecular. The thermal librations of the piperidine and methyl groups become considerably reduced at 170 K and nearly fully reduced at about 100 K. The IR spectra and polarised Raman spectra agree with the X-ray structure and confirm the disorder effect on the piperidine ring. The assignment of the bands observed was made on the basis of DFT chemical quantum calculations. Copyright

Recent advances in linear and nonlinear Raman spectroscopy. Part IV

“…Kumar et al [196] characterized the structure of the lead-free relaxor Ba(Ti 0.70 Sn 0.30 )O 3 using micro-Raman spectroscopy from 80 to 500 K, which indicated three local phase sequences. Raman spectral studies of the Zr 4+ -rich BaZr x Ti 1−x O 3 phase diagram are described by Karan et al [197] Lorenc et al [198] investigated the rotational disorder in 2-piperidyl-5-nitro-6-methylpyridine to specify its structural phase transition and its vibrational characteristics. Trzebiatowska-Gusowska et al [199] obtained a new complex containing sarcosine (CH 3 NH 2+ CH 2 COO − ) and barium(2+) dibromide (TSBB) in a 3 : 1 molar ratio, as well as its deuterated analog.…”