CHNHPbI: precise structural consequences of water absorption at ambient conditions.

The crystal structure of the pristine (I) and aged (II) crystals of CHNHPbI (hereafter MAPbI) hybrid organic-inorganic lead iodide has been studied at 293 K with high-precision single-crystal X-ray diffraction using a synchrotron light source. We show that (I) and (II) are characterized by an identical tetragonal unit cell but different space groups: I422 for (I) and P422 for (II). Both space groups are subgroups of I4/mcm, which is widely used for MAPbI. The main difference between (I) and (II) comes from the difference in hydrogen bonds between the MA cation and the PbI framework which is the direct consequence of HO insertion in the aged crystal (II).