This effect increases with the size of the A cation, with FA having a larger influence than MA, and the hardness of the anion, that enlarges the interaction between the B-site s orbitals and the anion p states , and consequently the tendency for activity of §https the lone pair, that results in a larger distortion of the octahedral environment. A similar trend was reported for MAPbI3, FAPbI3, MASnI3, FASnI3, MAPbBr3 and FAPbBr3 5 . It is worth noting that peak broadening and asymmetry are most pronounced for FASnBr3 (Panel D of figure ), where the Sn-Br distances are spread over a large range up to the typical values of the Br-Br interactions. In fact, the large peak centered at 4 Å results from the contribution of both the Sn-Br and Br-Br distances. The observed effects agree with the hypothesis that these compounds are subject to a dynamic off-centering of the B cation that is thermally activated and thus enhanced by temperature . In order to understand the underlying distortion in the local structure of these materials different models were tested against the room temperature data (RT). First of all, the aristotype perovskite structure in the Pm3¯m space group, which does not allow for octahedral tilting or displacement of the B cation, was taken into account. The RT PDF data fitted against this model led to poor agreement for all the samples (cf. Figure and Figures , 10 in ESI). This is not completely surprising since none of the MHPs investigated so far adopt a cubic structure at the local level, but rather a lower symmetry arrangement . Other tested models were the rhombohedral R3m, the tetragonal I4cm and I4/mcm, and the orthorhombic Pnma and Pmc21. In the rhombohedral symmetry there is no octhedral tilting, but the B cation is displaced along the [111] direction. The tetragonal models both introduce octahedral titling, but only I4cm allows for the displacement of the Bsite cation along the [001] direction. The orthorhombic models induce a further distortion in the octahedra with the displacement of the B cation along a diad axis. In the case of MASnI3 and FASnI3 (Figure and Figure in ESI) both the I4cm and R3m models provide good fits of the RT data and inspection of the different curves suggest that the rhombohedral distortion could better describe these compounds, as previously reported for MASnI3 and FASnI3 5 .