2D Homologous Series SrFM_<i>n</i>BiS_<i>n</i>+2 (M = Pb, Ag_0.5Bi_0.5; <i>n</i> = 0, 1) and Commensurately Modulated\nSr₂F₂Bi_2/3S₂

Abstract

We\nreport three new mixed-anion two-dimensional (2D) compounds:\nSrFPbBiS₃, SrFAg_0.5Bi_1.5S₃, and Sr₂F₂Bi_2/3S₂. Their\nstructures as well as the parent compound SrFBiS₂ were\nrefined using single-crystal X-ray diffraction data, with the sequence\nof SrFBiS₂, SrFPbBiS₃, and SrFAg_0.5Bi_1.5S₃ defining the new homologous series\nSrFM_<i>n</i>BiS_<i>n</i>+2 (M = Pb, Ag_0.5Bi_0.5; <i>n</i> =\n0, 1). Sr₂F₂Bi_2/3S₂ has\na different structure, which is modulated with a <b>q</b> vector\nof 1/3<i>b</i>* and was refined in superspace group <i>X</i>2/<i>m</i>(0β0)­00 as well as in the 1 ×\n3 × 1 superstructure with space group <i>C</i>2/<i>m</i> (with similar results). Sr₂F₂Bi_2/3S₂ features hexagonal layers of alternating [Sr₂F₂]²⁺ and [Bi_2/3S₂]^2–, and the modulated structure arises from the\nunique ordering pattern of Sr²⁺ cations. SrFPbBiS₃, SrFAg_0.5Bi_1.5S₃, and Sr₂F₂Bi_2/3S₂ are semiconductors with\nband gaps of 1.31, 1.21, and 1.85 eV, respectively. The latter compound\nexhibits room temperature red photoluminescence at ∼700 nm.