Mercury bismuth chalcohalides, Hg3Q2Bi2Cl8 (Q = S, Se, Te): syntheses, crystal structures, band structures, and optical properties.

Three quaternary mercury bismuth chalcohalides, Hg3Q2Bi2Cl8 (Q = S, Se, Te), are reported along with their syntheses, crystal structures, electronic band structures, and optical properties. The compounds are structurally similar with a layer comprised of a hole perforated sheet network of Hg3Q2 (Q = S and Te) that forms by fused cyclohexane, chairlike Hg6Q6 rings. The cationic charge in the network is balanced by edge-sharing monocapped trigonal-prismatic anions of Bi2Cl8 that form a two-dimensional network located between layers. Compound 1, Hg3S2Bi2Cl8, crystallizes in the monoclinic space group C12/m1 with a = 12.9381(9) Å, b = 7.3828(6) Å, c = 9.2606(6) Å, and β = 116.641(5)°. Compound 2, Hg3Te2Bi2Cl8, crystallizes in the monoclinic space group C12/c1 with a = 17.483(4) Å, b = 7.684(2) Å, c = 13.415(3) Å, and β = 104.72(3)°. The crystals of the Hg3Se2Bi2Cl8 analogue exhibit complex modulations and structural disorder, which complicated its structural refinement. Compounds 1 and 2 melt incongruently and show band gaps of 3.26 and 2.80 eV, respectively, which are in a good agreement with those from band-structure density functional theory calculations.