The compound Ba 2 Cu 2 ThS 5 has been synthesized by the reaction of BaS, S, Cu, and Th at 1173K. It crystallizes in the monoclinic space group C2h3−C2/m with two formula units in a cell of dimensions a=13.5616(8)Å, b=4.1159(2)Å, c=9.3548(6)Å, β=115.89(1)° (100K). The structure comprises Ba 2+ cations and [Cu2ThS54−]∞2 layers. The two dimensional layers are formed by the connection of ThS 6 octahedra and CuS 4 tetrahedra along [001] with a sequence…. oct tet tet oct tet tet…. Optical measurements performed on Ba 2 Cu 2 ThS 5 indicate an indirect band gap of 1.86eV. DFT calculations performed with the HSE06 functional yield band gaps of 1.7eV for Ba 2 Cu 2 ThS 5 and 1.5eV for the isostructural compound Ba 2 Cu 2 US 5 .