(Ag2TeS3)2•A2S6 (A = Rb, Cs): Layers of Silver Thiotellurite Intergrown with Alkali-Metal Polysulfides

The layered compounds RbAg2TeS6 and CsAg2TeS6 crystallize in the noncentrosymmetric space group P6(3)cm, with a = 19;15 angstrom, c = 14.64 angstrom, and V = 4648 angstrom(3) and a = 19.41 angstrom, c = 14.84 angstrom, and V = 4839 angstrom(3), respectively. The structures are composed of neutral [Ag2TeS3] layers alternating with charge-balanced salt layers containing polysulfide chains of [S-6](2-) and alkali-metal ions. RbAg2TeS6 and CsAg2TeS6 are air- and water-stable, wide-band-gap semiconductors (E-g similar to 2.0 eV) exhibiting nonlinear-optical second-harmonic generation.