Compression and probing C-H...I hydrogen bonds of iodoform under high pressure by X-ray diffraction and Raman scattering.

High-pressure methods were applied to investigate the structural stability and hydrogen bonding of polar molecules of iodoform by synchrotron radiation X-ray diffraction and Raman spectra measurements, respectively. Up to a pressure of 40 GPa, no phase transitions were observed. The discontinuous frequency shift of the C-H stretching band is believed to be related to the enhancement of the C-H...I weak hydrogen bonds under high pressures. Ab initio calculations were performed, and the results predict the frequency shift of the C-H stretching vibration as C-H...I interacts via hydrogen bonding. The bulk modulus is 17.3+/-0.8 GPa, with a pressure derivative of 5.2.