A new low temperature solid modification in 1-isothiocyanato-4-(trans‑4-propylcyclohexyl)benzene (3CHBT) probed by Raman spectroscopy and quantum chemical calculations.

Raman spectra of 1-isothiocyanato-4-(trans 4-propylcyclohexyl)benzene (3CHBT) were studied in the region, 1450-2300cm-1 at twenty two different temperatures in the range, 83-293K in cooling and heating cycles. All bands in this region were critically evaluated in term of linewidth, peak position and relative intensity. Raman bands at ~2085cm-1 and ~2120cm-1 shows clear evidence of a solid modification through anomaly in temperature dependence peak positions and linewidths variation in the temperature range 173-203K. A detailed analysis of the variation of the linewidth and peak position of the two component bands leads to the conclusion that the molecular/dimer arrangement in crystalline packing changed between 173K and 203K. This solid modification was also analyzed at the molecular level. The ~2085cm-1 and ~2120cm-1 bands were corresponded as parallel and anti-parallel dimers of 3CHBT, which are identified as dimer I (D1) and dimer II (D2), respectively. The structures of both the dimers have been optimized by quantum chemical calculations employing density functional theoretic (DFT) methods.