PbnI4n+2(2n+2)? ribbons (n = 3, 5) as dimensional reductions of 2D perovskite layers in cystamine cation based hybrids, also incorporating iodine molecules or reversible guest water molecules

Abstract

Pb_nI_4n+2 ^(2n+2)− (n = 3, 5) ribbons, which can be regarded as dimensional reductions of 2D perovskite layers, are stabilized by diprotonated cystamine cations in (NH₃(CH₂)₂SS(CH₂)₂NH₃)₄Pb₃I₁₄,I₂ (1) and (NH₃(CH₂)₂SS(CH₂)₂NH₃)₆Pb₅I₂₂·4H₂O (2). Both 1 and 2 have interesting structural characteristics; it is unprecedented that the ribbons are linked via I₂ molecules incorporated in the lattice of 1, while tetrameric water clusters are trapped in the structure of 2. 2 undergoes a (reversible) water desorption process at 310 K leading to (NH₃(CH₂)₂SS(CH₂)₂NH₃)₆Pb₅I₂₂·2H₂O (3). The electrical behavior of 2 and 3 has been investigated in the ranges 293–310 K and 310–358 K respectively. Above 310 K, the electronic contribution remains constant while the ionic transference number tends towards unity showing almost pure ionic transport at 360 K (6 × 10⁻⁷ S cm⁻¹ at 330 K) originating probably from the migration of protons through the hydrogen bonds connecting the water molecules to the cystamine counter cations.