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 S3(2-) ions. These molecular anions are charge-balanced by Ba(2+) cations. Raman spectroscopy shows three strong bands originating from symmetric, asymmetric, and bending vibrational modes of the S3(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.