Three new solid state silver selenoarsenates and one thioarsenate prepared from hydro- and methanothermal synthesis are described. β-Ag 3 AsSe 3 (I) and (Me 3 NH)[Ag 3 As 2 Se 5 ] (II) were synthesized hydrothermally at 110°C from a mixture of AgBF 4 /3K 3 AsSe 3 and AgBF 4 /3K 3 AsSe 3 /6Me 3 NHCl, while K 5 [Ag 2 As 3 Se 9 ] (III) and K[Ag 3 As 2 S 5 ] (IV) were synthesized methanothermally at 110°C from a mixture of AgBF 4 /3K 3 AsS 3 and AgBF 4 /3K 3 AsSe 3 , respectively. β-Ag 3 AsSe 3 (I) crystallizes in the orthorhombic space groupPnma(No. 62) witha= 8.111(1) Å,b= 11.344(2) Å,c= 20.728(3) Å,Z= 8,V= 1907(1) Å 3 . This compound is a new allotrope of α-Ag 3 AsSe 3 and has a complex three-dimensional structure composed of distorted trigonal planar and tetrahedral Ag + ions and [AsSe 3 ] 3− units. (Me 3 NH)[Ag 3 As 2 Se 5 ] (II) crystallizes in the triclinic space groupP− 1 (No. 2) witha= 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) Å 3 . The [Ag 3 As 2 Se 5 ] n− n anion in (II) has a complex two-dimensional layered structure with tetrahedral Ag + ions and [As 2 Se 5 ] 4− units. K 5 [Ag 2 As 3 Se 9 ] (III) crystallizes in the orthorhombic space groupPnma(No. 62) witha= 12.599(2) Å,b= 12.607(4) Å,c= 14.067(3) Å,Z= 8,V= 2234(1) Å 3 . The [Ag 2 As 3 Se 9 ] 5 n− n anion in (III) has a two-dimensional layered structure with tetrahedral Ag + ions and two different kinds of selenoarsenate units, [AsSe 4 ] 3− and [As 2 Se 5 ] 4− . K[Ag 3 As 2 S 5 ] (IV) also crystallizes in the orthorhombic space groupPnma(No. 62) witha= 19.210(2) Å,b= 16.867(2) Å,c= 6.3491(7) Å,Z= 8,V= 2057.2(7) Å 3 . The [Ag 3 As 2 S 5 ] n− n anion in (IV) possesses a complicated two-dimensional structure with tetrahedral Ag + ions and two kinds of thioarsenate ligands, [AsS 3 ] 3− and [As 3 S 7 ] 5− . The thermal stability and optical absorption properties of these compounds are reported.