Structural response of diiodobutenyl-bis-thioquinolinium triiodide to high pressure and theoretical study of mechanical properties†

The response of the diiodobutenyl-bis-thioquinolinium triiodide crystal structure to hydrostatic compression from 1 atm to 4 GPa and mechanical stress was studied using experimental techniques (Raman and Brillouin spectroscopy, single-crystal X-ray diffraction) and periodic DFT modeling. A phase transformation above 2.5(1) GPa manifested itself by abrupt changes in the unit cell parameters and non-merohedral twinning. The changes in the band positions in the low-wavenumber region of Raman spectra were attributed to a change in the bridging hydrogen position in the N⋯H⋯N fragment and to the changes in the anion. The DFT modeling of the crystal structure on compression revealed the changes in the structural fragments that can explain why a high-pressure phase transition takes place.