Synthesis, crystal structures, and optical properties of NaCdPnS3 (Pn = As, Sb)

Two compounds NaCdPnS3 (Pn = As (1), Sb (2)) were synthesized as transparent yellow and red platelets by reacting cadmium powder with the molten mixtures of Na2S/As2S3/S and Na2S/Sb/S at 500 °C. Both compounds are plagued with crystal twinning and acceptable crystal structure refinement could only be obtained by identifying the type of the twinning laws. NaCdAsS3 (1) crystallizes in the monoclinic space group P21/n (no. 14) with a = 5.6561(8), b = 16.5487(15), c = 5.6954(8) Å, β = 90.315(11)°, and Z = 4. NaCdSbS3 (2) crystallizes in the monoclinic space group C2/c (no. 15) with a = 8.1329(6), b = 8.1296(4), c = 17.2600(13) Å, β = 103.499(6)°, and Z = 8. The structures of both compounds feature a 2∞[CdPnS3]− layer composed of [CdS4] tetrahedra and [AsS3] or [SbS3] pyramidal units. Between the 2∞[CdPnS3]− (Pn = As, Sb) layers the Na+ cations reside in a distorted octahedral environment of S atoms. Compound 1 is characterized with UV/Vis diffuse reflectance spectroscopy and IR and Raman spectra.

► Layered anions constructed by [CdS4] tetrahedra and [PnS3] pyramids (Pn = As, Sb).
► The Sb atom exhibits a 3+3 coordination geometry.
► Weak interlayer Sb–S contact generates a three-dimensional network.
► Structural differences due to different stereochemical activity of lone electron pair.