Guest dependent Brillouin and Raman scattering studies of zeolitic imidazolate framework-8 (ZIF-8) under external pressure.

We have investigated the pressure dependence of the acoustic modes of zeolitic imidazolate framework (ZIF-8) in different pressure transmitting mediums and also under non-hydrostatic conditions using high pressure Brillouin spectroscopy. Our study shows the pressure induced flexibility and dynamics of ZIF-8 framework as well as a huge increase in the acoustic velocities on applying external pressure, illustrating the role of guest in enhancing the elastic properties of the framework. In fact, the elastic constant C11 of the guest incorporated ZIF-8 increases by ∼183% on applying a pressure of only 1.47 GPa. The pressure transmitting medium also plays an important role in controlling the gate opening behaviour of ZIF-8. Pressure dependent Raman study shows significant changes in the modes of ZIF-8 as well as that of that of the pressure transmitting medium which is entrapped within the framework, indicating that the interaction between the framework and guest is responsible for the medium dependent changes observed in the Brillouin spectra.