Two 3D Rubidium Halide Organic-Inorganic Hybrid Perovskite Ferroelectrics Templated by Quasi-Spherical Organic Amine 1,4-Diazabicyclo[3.2.2]nonane.

The emergence of (CH NH )PbI has brought the development of three-dimensional (3D) organic-inorganic hybrid perovskite (OIHP) structures with ABX type to a higher level; however, most 3D frameworks are constructed by corner-sharing of BX octahedra. Herein, we substituted the spherical molecule 1,4-diazabicyclo[2.2.2]octane (2.2.2-dabco) with 1,4-diazabicyclo[3.2.2]nonane (1,4-3.2.2-dabcn) as a template to react with RbX (X=Br, I) in the corresponding HX acids under the consideration of reducing the molecular symmetry. Two 3D OIHP compounds [1,4-3.2.2-H dabcn]RbI ⋅H O (1) and [1,4-3.2.2-H dabcn]RbBr (2) crystallized in non-centrosymmetric point group mm2 before the phase transition point were isolated. Among them, the 3D inorganic framework of 1 is constructed by sharing the corner of [RbI ] octahedra, while that of 2 is constructed by sharing the corner and face of [RbBr ] octahedra to acquire large cavities to accommodate the organic amine cation [1,4-3.2.2-H dabcn] ; this 3D framework type is unprecedented in the OIHPs. As expected, compounds 1 and 2 exhibit reversible phase transition, dielectric and second harmonic generation (SHG) and ferroelectric properties, in which the phase transition temperature of 2 at 374 K is much higher than compound 1 at 280 K.