Ba₂HgS₅-A molecular trisulfide salt with dumbbell-like (HgS₂)^2- ions

Ba₂HgS₅ was synthesized by cooling a molten mixture of BaS, HgS, and elemental sulfur. It crystallizes in the orthorhombic Pnma space group with a = 12.190(2) Å, b = 8.677(2) Å, c = 8.371(2) Å, and d_calc = 4.77 g cm^-3. Its crystal structure consists of isolated dumbbell-shaped (HgS₂)^2- and v-shaped S₃^2- ions. These molecular anions are charge-balanced by Ba²⁺ cations. Raman spectroscopy shows three strong bands originating from symmetric, asymmetric, and bending vibrational modes of the S ₃^2- ions. X-ray photoelectron spectroscopic analysis confirms the presence of the trisulfide species. Ba₂HgS₅ has a bandgap of ∼2.4 eV. Electronic band structure calculations show that the bandgap is defined essentially by the p-orbitals of the sulfur atoms of the S₃^2- group.