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 dcalc = 4.77 g cm–3. Its crystal structure consists of isolated dumbbell-shaped (HgS2)2– and v-shaped S32– 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 S32– 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 S32– group.