Methylhydrazinium lead iodide – one dimensional chain phase with excitonic absorption and large energy band gap

Abstract

In this work the crystal structure of the new hybrid organic-inorganic compound has been studied using single-crystal X-ray diffraction (SCXRD). Methylhydrazinium lead iodide (MHyPbI3) crystallizes in monoclinic, centrosymmetric P21/c space group with a = 4.5067(4) Å, b = 19.1892(16) Å, c = 12.0029(12) Å and β = 98.178(8)°. The structure is built of edge-sharing [PbI6]4− octahedra forming parallel double chains along the [100] direction. MHy+ cations are placed between the chains. The motif is stabilized via two kinds of NH···I hydrogen bonds. RT absorption studies reveal the excitonic absorption band at 413 nm (3.00 eV). The estimated energy band gap value Eg is 3.11 eV (400 nm). At 367 K MHyPbI3 transforms to the new HT polymorph of P21/m symmetry with a = 8.895(1) Å, b = 18.185(1) Å and c = 13.197(1) Å and β = 99.10(1)°, that corresponds to the 2a monoclinic superstructure of the RT phase. The HT polymorph is metastable and returns to the pristine RT phase after ca. 50 min at room temperature.