Structural and physical properties of two distinct 2D lead halides with intercalated Cu(ii)

Transition metal cation intercalation between the layers of two-dimensional (2D) metal halides is an underexplored research area. In this work we focus on the synthesis and physical property characterizations of two layered hybrid lead halides: a new compound [Cu(O₂C-CH₂-NH₂)₂]Pb₂Br₄ and the previously reported [Cu(O₂C-(CH₂)₃-NH₃)₂]PbBr₄. These compounds exhibit 2D layered crystal structures with incorporated Cu²⁺ between the metal halide layers, which is achieved by combining Cu(ii) and lead bromide with suitable amino acid precursors. The resultant [Cu(O₂C-(CH₂)₃-NH₃)₂]PbBr₄ adopts a 2D layered perovskite structure, whereas the new compound [Cu(O₂C-CH₂-NH₂)₂]Pb₂Br₄ crystallizes with a new structure type based on edge-sharing dodecahedral PbBr₅O₃ building blocks. [Cu(O₂C-CH₂-NH₂)₂]Pb₂Br₄ is a semiconductor with a bandgap of 3.25 eV. It shows anisotropic charge transport properties with a semiconductor resistivity of 1.44 × 10¹⁰ Ω cm (measured along the a-axis) and 2.17 × 10¹⁰ Ω cm (along the bc-plane), respectively. The fabricated prototype detector based on this material showed response to soft low-energy X-rays at 8 keV with a detector sensitivity of 1462.7 μCGy⁻¹ cm⁻², indicating its potential application for ionizing radiation detection. These encouraging results are discussed together with the results from density functional theory calculations, optical, magnetic, and thermal property characterization experiments.