Preparation, crystal structure and characterization of α-NaSbP2S6 and β-NaSbP2S6 phases

The new phases α-NaSbP2S6 and β-NaSbP2S6 were synthesized by ceramic and reactive flux methods at 773 K. The structures of α-NaSbP2S6 and β-NaSbP2S6 were determined by the single-crystal X-ray diffraction technique. α-NaSbP2S6 crystallizes in the monoclinic space group P21/c with a = 11.231(2) A, b = 7.2807(15) A, c = 11.640(2) A, β = 108.99(3)o, V = 900.0(3) A3 and z = 4. β-NaSbP2S6 crystallizes in the monoclinic space group P21 with a = 6.6167(13) A, b = 7.3993(15) A, c = 9.895(2) A, β = 92.12(3) o, V = 484.10(17) A3 and z = 2. The α- and β-phases of NaSbP2S6 are closely related, the main difference lies in the stacking of the [Sb[P2S6]] nn- layers. The structure of α-NaSbP2S6 consists of two condensed layers (MPS3 type) to give an ABAB... sequence with Na+ cations located in the interlayer space. The packing of β-NaSbP2S6 is formed by monolayers of [Sb[P2S6]] nn- stacked in an AA... fashion separated by a layer of Na+ cations. Both phases are derivates of the M1+M3+P2Q6 family. The optical band gaps of α-NaSbP2S6 and β-NaSbP2S6 were determined by UV-vis diffuse reflectance measurements to be 2.17 and 2.25 eV, respectively