We further explored alloying strategies by tuning the halide content Br/I on the Cs3Sb2Br9 perovskite. While such strategy has been explored for the Bi analogue, no studies are reported for the Sb-based composition. For this purpose, samples of the Cs3Sb2Br9-xIx system for x= 0 (also reported above), 2.5, 4.5, 6.5, and 9 have been synthesized by means of mechanochemistry according to the experimental conditions reported in the SI. Photographs of the five samples are reported in Figure . The XRD patterns of the whole series of samples are reported in Figure . For the Cs3Sb2I9 perovskite two different polymorphs have been reported, namely the layered modification with s.g. (space group) P-3m1 (analogous to Cs3Sb2Br9, see above) and the dimer modification with space group P63/mmc, featuring SbI6 octahedra fused into Sb2I9 3-dimers through sharing of their triangular faces. According to literature, the dimer form is synthesized from solution using a polar solvent, whereas the layered form is obtained from a solid state reaction at low temperatures. However, the present synthetic approach has never reported before for Cs3Sb2I9 and additional information on the stability of the different polymorphs have been obtained. According to Figure , reporting the XRD patterns of Cs3Sb2I9 perovskite against the expected structure for the P-3m1 space group, we could obtain the layered modification through mechanochemistry. However, this was possible after optimizing the synthesis approach in terms of milling cycles and time. As a way of example, All the data follow a linear trend as a function of the iodide content, according to the Vegard's law, confirming the formation of a continuous solid solution in this system in analogy with the analogous Bi-based system. a) b) c) The observed expansion of the unit cell together with the progressive substitution of the Br atoms with a heavier one leads again to a clear redshift of the Raman modes, more pronounced with respect to what observed when Bi/Sb are replaced at the B sites, as above described. From Figure this behavior is particularly evident for the mode at 210 cm -1 proper of the Cs3Sb2Br9 structure: its center shifted till 185 cm -1 for x = 6.5 sample, then it completely disappears in the Cs3Sb2I9 compound.