Polymorphism and Red Photoluminescence Emission from 5s 2 Electron Pairs of Sb(III) in a New One-Dimensional Organic-Inorganic Hybrid Based on Methylhydrazine: MHy 2 SbI 5 .

We explore the crystal structure and luminescent properties of a new 1D organic-inorganic hybrid, MHy 2 SbI 5 , based on methylhydrazine. The compound reveals the red photoluminescence (PL) originating from the 5s 2 electron pairs of Sb(III) as well as complex structural behavior. MHy 2 SbI 5 crystalizes in two polymorphic forms ( I and II ) with distinct thermal properties and structural characteristics. Polymorph I adopts the acentric P 2 1 2 1 2 1 chiral space group confirmed by SHG, and, despite a thermally activated disorder of MHy, does not show any phase transitions, while polymorph II undergoes reversible low-temperature phase transition and high-temperature reconstructive transformation to polymorph I . The crystal structures of both forms consist of 1D perovskite zig-zag chains of corner-sharing SbI 6 octahedra. The intriguing phase transition behavior of II is associated with the unstable arrangement of the [SbI 5 ] 2- ∞ chains in the structure. The energy band gap (E g ) values, estimated based on the UV-Vis absorption spectra, indicate that both polymorphs have band gaps, with E g values of 2.01 eV for polymorph I and 2.12 eV for polymorph II .