Fig. 4. MAS NMR and far-IR spectroscopic characterization.

a Slices along the indirectly detected dimension through the 2D ¹H-¹³C spin-diffusion solid state NMR spectra of crystalline ZIF-8-mim_0.15im_0.74bim_0.11 (top) and glassy a_gZIF-8-mim_0.15im_0.74bim_0.11 (bottom). Slices were taken at a ¹H chemical shift of 1.5 ppm and normalized to the peak area of –CH₃. The slices show the polarization transfer from the protons of the –CH₃ groups of mim^– to all ¹³C atoms in the samples as a function of the mixing time. Blue lines represent the slices obtained with a spin-diffusion mixing time of 90 µs, red lines correspond to a mixing time of 5000 µs, and gradually increasing grey lines correspond to mixing times of 360, 540, 1000 and 2000 µs. b Comparison of the spin-diffusion polarization transfer processes in the crystalline and glassy states. Peach-colored labels in a and b represent intramolecular polarization transfers within mim^–, while purple labels represent inter-linker polarization transfers from mim^– to im^– or bim^–. Dashed lines are exponential fits to the data. c Far-IR spectra of ZIF-8, ZIF-8-mim_0.15im_0.74bim_0.11 and a_gZIF-8-mim_0.15im_0.74bim_0.11.