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 2.63eV, respectively. (HIm)2Hg3Cl8 and (HIm)HgI3 are broadband light emitters with broad photoluminescence peaks centered at 548nm (2.26eV) and 582nm (2.13eV), respectively. Following the crystal and electronic structure considerations, the PL peaks are assigned to self-trapped excitons.