In the last years there has been a growing interest around layered or two-dimensional (2D) metal halide perovskite (MHPs) for their superior stability and rich structural diversity, which may found application in several devices spanning from photovoltaics to lasing. The most investigated families of 2D perovskites are the Ruddlesden-Popper (RP) and Dion-Jacobson (DJ) phases of general formula A′2An-1MnX3n+1 and A′An-1MnX3n+1, respectively, where A′ and A are organic cations, and n represents the number of staggered inorganic layers made of metal M and halide X. Most of the investigated organic spacers for 2D perovskites, to date, are monoammonium cations, while diammonium cations have been less explored. In the latter case, and in particular for short cations, the DJ phases are generally formed, where the inorganic layers are stacked in an eclipsed fashion on top of each other, differently from RP where they are staggered. In addition, not always a diammonium cation stabilizes a 2D perovskite, and 1D structures, characterized by linear chains of octahedra, have been also often observed. For example, in the series of linear cations of general formula NH3(CH2)mNH3 2+ (m = 4, 7, 8, 10, 12), the cations with even carbon-chain lengths formed 2D perovskites, while those with odd carbon chain lengths formed a 1D structure. Very recently, the structural diversity of systems incorporating a diammonium cations has been further expanded towards 3D halide perovskitoids using linear cations such as 1,4-butanediamine (1,4BDA), N,Ndimethyl-1,3-propanediamine (NMPA), or N,Ndimethylethylenediamine (DMEA) providing a structural motif comprising dimers with edge-sharing octahedra which are then connected through corner-sharing bond to form a 3D network. In these systems, the optical properties are close to traditional 3D MHPs with the bandgap being mainly influenced by standard octahedra distortion parameters. The correlation between structural distortions and optical properties in 2D perovskites is a key topic to modulate their properties and design novel and optimized materials. Thanks to the vast work performed on perovskites including monoammonium cations, well-defined parameters have been defined and a careful materials design is now possible. On the other hand, such kind of correlation is still partially missing on perovskites including a diammonium cations. In this context, the most relevant studies have been carried out on some limited compositions including, for example, 2,2′-(ethylenedioxy)bis(ethylammonium) (EDBE), N 1 -methylethane-1,2-diammonium (N-MEDA), and 3-(2-ammonioethyl)anilinium (AEA) due to the interest in their very broad (white) emission. In (EDBE)PbBr4, the strong structural distortion induced by the organic spacer closely affects its defectivity leading to the formation of VF centers whose radiative decay ultimately leads to broadened photoluminescence (PL). In the other Pb-Br lead perovskites, where crystal structure was solved by x-ray diffraction (XRD) on single crystals, the broadband emission was as well correlated to self-trapping of photogenerated carriers through excitedstate lattice distortions. The work of Smith and co-workers put in prominence, among other structural parameters, the influence, on the relative intensity of the broad emission, of the distortion along the Pb-Br-Pb bond axis. These results on diammonium cations further confirm, also for this type of ditopic ligands, the possibility of inducing slight distortions in the inorganic lattice by playing with the nature of the organic cation and therefore finely modulating the optical properties. However, the set of available structural data from single crystal diffraction and their correlation with optical propertieson diammonium cations is still limited. In this work we enlarge the family of Pb-Br layered perovskites by a systematic and rationale investigation of the four diammonium cations represented in Figure The first two spacers have been recently investigated in Pb-I and Pb-Br thin films highlighting their improved moisture resistance (in particular for 1,4-XDA). In absence of single crystal XRD data, it was concluded that the systems based on 1,4-PDA did not form a well-defined layered structure, due to the lack of flexibility of the PDA spacer, as well as its lower level of penetration into the neighboring perovskite layers, which prevents the formation of a layered phase. Optical bandgap was reported to increase with the length of the alkyl chain but a clear correlation with optical properties was hindered by the lack of any structural data. Concerning the 1,3-PDA and 1,3-XDA, the first cation has been investigated in Pb-I 2D perovskites as a function of the number of inorganic layers, n, (providing the crystal structure),