(Ag2TeS3)2·A2S6 (A = Rb, Cs): layers of silver thiotellurite intergrown with alkali-metal polysulfides.

The layered compounds RbAg(2)TeS(6) and CsAg(2)TeS(6) crystallize in the noncentrosymmetric space group P6(3)cm, with a = 19.15 Å, c = 14.64 Å, and V = 4648 Å(3) and a = 19.41 Å, c = 14.84 Å, and V = 4839 Å(3), respectively. The structures are composed of neutral [Ag(2)TeS(3)] layers alternating with charge-balanced salt layers containing polysulfide chains of [S(6)](2-) and alkali-metal ions. RbAg(2)TeS(6) and CsAg(2)TeS(6) are air- and water-stable, wide-band-gap semiconductors (E(g) ∼ 2.0 eV) exhibiting nonlinear-optical second-harmonic generation.