Structures of (4-Y‑C₆H₄CH₂NH₃)₂PbI₄ {Y = H, F, Cl, Br, I}: Tuning of Hybrid Organic Inorganic Perovskite Structures from Ruddlesden–Popper to Dion–Jacobson Limits

In analogy to their oxide counterparts, two-dimensional (2D) hybrid organic–inorganic perovskites have been classified, in many cases, as either Dion–Jacobson (DJ) or Ruddlesden–Popper (RP) structures. We quantified the offset of the inorganic layers to allow the structures of hybrid organic inorganic perovskite to be consistently related to these two structure types. We report the structures of a family of 2D hybrid structures, (4-Y-C₆H₄CH₂NH₃)₂PbI₄ (where Y = F, Cl, Br, I), which consist of single ⟨100⟩-terminated perovskite sheets separated by p-halobenzylammonium cations. In contrast to the previous RP structure of (C₆H₅CH₂NH₃)₂PbI₄, where the inorganic layers are offset from each other, the Y = F, Cl, and Br examples tend toward the DJ structure, in which successive layers eclipse each other, despite the use of an organic monocation. Close Y···I approaches suggest that halogen bonding plays a role in these structures. Use of Y = I, for which stronger halogen bonding is expected and is also suggested by a more linear C–Y···I angle, results in an RP-like structure. The stability of the (4-Y-C₆H₄CH₂NH₃)₂PbI₄ derivatives under ambient conditions is substantially higher for Y = Br and I than for Y = H, F, and Cl.