Figure plots the computed longitudinal piezoelectric coefficients d 33 against shear piezoelectric coefficients d 16 , d 24 , d 25 for the plastic ionic molecular crystals and makes a comparison with data for the five inorganic piezoelectrics for five inorganic materials: PbTi and BaTiO 3 in the tetragonal P4mm phase, LiNbO 3 in the rhombohedral R3c phase, wurtzite AlN and ZnO, and HfO 2 in the ortorhombic Pca2 1 phase. Data for the first 4 extracted from the Materials Project databases of computed material properties, while HfO 2 data is obtained from Dutta et al. . The comparison highlights how the plastic ionic molecular crystals studied here have generally smaller d 33 values than the inorganics, but the piezoelectric shear coefficients d 16 , d 24 ,d 25 have similar or larger magnitude, hence large piezoelectric anisotropy factors. We note that the d 33 of the inorganic materials within the materials project are for 0 K conditions in phase-pure single crystalline form and can be significantly lower than experimental values for polycrystalline samples with extrinsic contributions from mechanisms such as domain wall movement. Experiments made phase pure high-quality samples show better agreement with theory. Figure plots the shear piezoelectric coefficients d 16 , d 24 , d 25 against the corresponding shear compliance coefficients c 44 , c 55 , c 66 for the materials studied. For the plastic ionic crystals, high shear compliance coefficients typically coincide with high shear piezoelectric response. This trend supports the key role of molecular rotation in the piezoelectric response from most of plastic ionic crystals. The material with the largest shear piezoelectric response, HQReO 4 with d 16 = -94 pC/N has c 66 of 505 TPa -1 , while [F -Q]ReO 4 with similar packing and composition has d 16 = -33 pC/N with c 66 = 187 TPa -1 . While the HQ compound has an anisotropy of 118, [F -Q] has an anisotropy of 7, underlining the more important role of molecular rotation for the former.