AbstractThe discovery of new 3D perovskites and their 2D and 1D analogues continues to attract the interest of the scientific community and therefore the understanding of their structural, optical, and physicochemical properties is of fundamental importance. Here, we report the one‐pot synthesis and the full characterization of 1D and 2D lead halide polycrystalline solids containing the rather rigid 1,4‐xylylenediammonium (pXDA) organic cation as spacer. We isolated 2D Dion‐Jacobson (DJ) perovskites, namely (pXDA)PbX₄ (X=Cl, Br) and the mixed halide (pXDA)Pb(Br_1–xI_x)₄ species (all based on 2D monolayers of corner‐sharing lead halide octahedra), and, for iodine, the (pXDA)Pb₂I₆ . 2H₂O phase, which contains 1D ribbons. The latter species can be reversibly dehydrated by gentle heating, forming the isomorphous (pXDA)Pb₂I₆. crystal phase. These species, some of which have recently been studied in the frame of broad light emitters and for photovoltaic applications, have been characterized by variable‐temperature X‐ray diffraction methods, shedding light onto their anisotropic thermal responses, of utmost importance for day‐night cycling in functional devices. Spin‐coated thin films were also prepared and studied by means of synchrotron radiation grazing incidence X‐ray diffraction, SEM imaging and fluorescence spectroscopy experiments.