The preference for the rhombohedral model is more pronounced for FASnI3 rather than MASnI3, which is well reproduced also by the I4cm (Figure and Figure in ESI), as in the case of MAPbI3 . The rhombohedral model is fairly common in the world of all-inorganic perovskites as, for example, in several well-known titanates, both in the local and average structure , in CsSnBr3 , and was also proposed to describe the local structure of FASnBr3 5 . Both the tetragonal and rhombohedral models induce a displacement of the Bsite cation, suggesting that its off-centering is needed to properly describe the local structure, and clearly indicating that the cubic model is not sufficient. The space groups of the respective low temperature phases, I4/mcm for MASnI3 and Pnma for FASnI3, were also tested (Figures and in ESI), since both MAPbBr3 and MAPbCl3 were reported to show the structure of their low temperature phase in the local range . However, none of these models led to an improvement of the fit to the experimental data. As already pointed out, the distortion increases moving from the iodide to the bromide compounds, making the choice of a good structural model more difficult for this second group. In the case of MASnBr3 the Pm3¯m is not able to reproduce the experimental trends, whereas the R3m and I4cm models give better results (Figure in ESI). However, the Pmc21 model, the same structure of the low temperature phase , provides the best fit of the clear splitting of the Sn-Br correlation (Figure ).