Mercury bismuth chalcohalides, Hg₃Q₂Bi ₂Cl₈ (Q = S, Se, Te): Syntheses, crystal structures, band structures, and optical properties

Three quaternary mercury bismuth chalcohalides, Hg₃Q ₂Bi₂Cl₈ (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 [Hg₃Q ₂]²⁺ (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 [Bi ₂Cl₈]^2- that form a two-dimensional network located between layers. Compound 1, Hg₃S₂Bi ₂Cl₈, 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, Hg₃Te₂Bi ₂Cl₈, 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 Hg₃Se₂Bi ₂Cl₈ 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.