Isolation of β-Ag₃AsSe₃, (Me₃NH)[Ag₃As₂Se₅], K₅Ag₂As₃Se₉, and KAg₃As₂S₅: Novel solid state silver thio- and selenoarsenates from solvento-thermal synthesis

Three new solid state silver selenoarsenates and one thioarsenate prepared from hydro- and methanothermal synthesis are described. β-Ag₃AsSe₃ (I) and (Me₃NH)[Ag₃As₂Se₅] (II) were synthesized hydrothermally at 110°C from a mixture of AgBF₄/3K₃AsSe₃ and AgBF₄/3K₃AsSe₃/6Me₃NHCl, while K₅[Ag₂As₃Se₉] (III) and K[Ag₃As₂S₅] (IV) were synthesized methanothermally at 110°C from a mixture of AgBF₄/3K₃AsS₃ and AgBF₄/3K₃AsSe₃, respectively. β-Ag₃AsSe₃(I) crystallizes in the orthorhombic space group Pnma (No. 62) with a = 8.111(1) Å, b = 11.344(2) Å, c = 20.728(3) Å, Z = 8, V = 1907(1) ų. This compound is a new allotrope of α-Ag₃AsSe₃ and has a complex three-dimensional structure composed of distorted trigonal planar and tetrahedral Ag⁺ ions and [AsSe₃]^3- units. (Me₃NH)[Ag₃As₂Se₅] (II) crystallizes in the triclinic space group P - 1 (No. 2) with a = 10.119(2) Å, b = 18.010(4) Å, c = 14.932(3) Å, α = 110.20 (1)°, β = 103.98(2)°, γ = 99 99(1)°, Z = 2, V = 729.3(8) ų. The [Ag₃As₂Se₅]^n-_n anion in (II) has a complex two-dimensional layered structure with tetrahedral Ag⁺ ions and [As₂Se₅]^4- units. K₅[Ag₂As₃Se₉] (III) crystallizes in the orthorhombic space group Pnma (No. 62) with a = 12.599(2) Å, b = 12.607(4) Å, c = 14.067(3) Å, Z = 8, V = 2234(1) ų. The [Ag₂As₃Se₉]^5n-_n anion in (III) has a two-dimensional layered structure with tetrahedral Ag⁺ ions and two different kinds of selenoarsenate units, [AsSe₄]^3- and [As₂Se₅]^4-. K[Ag₃As₂S₅] (IV) also crystallizes in the orthorhombic space group Pnma (No. 62) with a = 19.210(2) Å, b = 16.867(2) Å, c = 6.3491(7) Å, Z = 8, V = 2057.2(7) ų. The [Ag₃As₂S₅]^n-_n anion in (IV) possesses a complicated two-dimensional structure with tetrahedral Ag⁺ ions and two kinds of thioarsenate ligands, [AsS₃]^3- and [As₃S₇]^5-. The thermal stability and optical absorption properties of these compounds are reported.