The new phases alpha-NaSbP2S6 and beta-NaSbP2S6 were synthesized by ceramic and reactive flux methods at 773 K. The structures of alpha-NaSbP2S6 and beta-NaSbP2S6 were determined by the single-crystal X-ray diffraction technique. alpha-NaSbP2S6 crystallizes in the monoclinic space group P2(1)/c with a = 11.231(2) angstrom, b = 7.2807(15) angstrom, c = 11.640(2) angstrom, beta = 108.99(3)degrees, V = 900.0(3) angstrom(3) and z = 4. beta-NaSbP2S6 crystallizes in the monoclinic space group P2(1) with a = 6.6167(13) angstrom, b = 7.3993(15) angstrom, c = 9.895(2) angstrom, beta = 0 92.12(3)degrees V = 484.10(17) angstrom(3) and z = 2. The alpha- and beta-phases of NaSbP2S6 are closely related, the main difference lies in the stacking of the [Sb[P2S6]](n)(n-) layers. The structure of alpha-NaSbP2S6 consists of two condensed layers (MPS3 type) to give an ABAB ... sequence with Na+ cations located in the interlayer space. The packing of beta-NaSbP2S6 is formed by monolayers of [Sb[P2S6]](n)(n-) stacked in an AA ... fashion separated by a layer of Na+ cations. Both phases are derivates of the M(1+)M(3+)P(2)Q(6) family. The optical band gaps of alpha-NaSbP2S6 and beta-NaSbP2S6 were determined by UV-vis diffuse reflectance measurements to be 2.17 and 2.25 eV, respectively. (C) 2006 Elsevier Ltd. All rights reserved.