Synthesis, crystal and electronic structures and optical properties of (HIm)₂Hg₃Cl₈ and (HIm)HgI₃ (HIm = imidazolium)

We report synthesis, crystal and electronic structures, and optical properties of two new Hg-based zero-dimensional hybrid organic-inorganic halides (HIm)₂Hg₃Cl₈ and (HIm)HgI₃ (HIm = imidazolium). (HIm)₂Hg₃Cl₈ crystallizes in the triclinic P-1 space group with a pseudo-layered structure made of organic imidazolium cation layers and anionic inorganic layers containing [Hg₂Cl₆]^2- units and linear [HgCl₂]⁰ molecules. (HIm)HgI₃ crystallizes in the monoclinic P2₁/c space group featuring anionic [HgI₃]^- units that are surrounded by imidazolium cations. Based on density functional theory calculations, (HIm)₂Hg₃Cl₈ has an indirect band gap, whereas (HIm)HgI₃ has a direct band gap with the measured onsets of optical absorption at 3.43 and 2.63 eV_, respectively. (HIm)₂Hg₃Cl₈ and (HIm)HgI₃ are broadband light emitters with broad photoluminescence peaks centered at 548 nm (2.26 eV) and 582 nm (2.13 eV), respectively. Following the crystal and electronic structure considerations, the PL peaks are assigned to self-trapped excitons.