Strong Second Harmonic Generation from the Tantalum Thioarsenates A3Ta2AsS11 (A = K and Rb)

The strongly anisotropic thioarsenates A(3)Ta(2)AsS(11) are stabilized in a polysulfide flux. All compounds contain the same parallel (1)/-[Ta2AsS113-] polymeric anionic chains, but the size of the alkali-metals has a profound effect on the packing of the chains. The K+ or Rb+ favor noncentrosymmetric packing of the chains, whereas the larger Cs+ favors the centrosymmetric packing. The chains feature the combination of two asymmetric units [Ta2S11] and [AsS3] and exhibit strong nonlinear optical (NLO) second harmonic generation.