Eight quaternary selenites and tellurites of antimony(V), ASb3X2O12 (A = K, Rb, Cs, Tl; X = Se, Te), have been synthesized by solid state reactions and structurally characterized by single crystal X-ray diffraction. They are isostructural compounds, which crystallize in the polar noncentrosymmetric P63 mc space group with hexagonal unit cell parameter values in the ranges of a = 7.1538(1)–7.2429(1) Å and c = 11.8978(4)–12.0478(3) Å. Their noncentrosymmetric layered structure consists of hexagonal-tungsten-oxide-related (Sb3X2O12)− layers interleaved with A+ ions. They have optical band gap values of 2.90–4.46 eV and showed powder second harmonic generation response equivalent to 1.0–37.2 × KDP.

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