From Cc to P63mc: Structural Variation in La3S2Cl2[SbS3] and La3OSCl2[SbS3] Induced by the Isovalent Anion Substitution

Abstract

The first antimony oxychloride sulfide, namely, La3OSCl2[SbS3], has been designed by isovalent anion substitution strategy. It belongs to the polar hexagonal space group P63mc (No. 186) with a = 9.327(5) Å, c = 7.075(5) Å, V = 533.0(5) Å3, and Z = 2. It is composed of three-dimensional (3D) cationic [La3OSCl2]3+ networks hosting covalent [SbS3] molecular anions. The 3D cationic [La3OSCl2]3+ are formed by the one-dimensional (1D) hexagonal columns of corner-shared [(Cl/S)La3] polyhedra propagating along the 63 axis situated in (0,0,z) and [OLa3] trigonal pyramids via corner-sharing. Moreover, the alternating [SbS3] and [OLa3] trigonal pyramids are arranged along the 3-fold axis located at (1/3, 2/3, z), generating a dipole moment component along the c-direction. Another remarkable structural motif is the occurrence of the empty octahedra formed by the disordered Cl/S anions, which further share the face to form 1D chains extending along the 63 axis located at (0,0,z). Interestingly, the occurrence of the isolated [La3SbOS3]4+ cubane-like clusters instead of the “chains of [La3SbOS3]4+” make the title compound distinct from the related La4OCl2S4 featuring common chains of [La4OS3]4+. The preliminary nonlinear optical (NLO) measurement indicates a moderate second-harmonic-generation (SHG) signal (ca. 0.7 × AgGaS2) at 2050 nm laser. Moreover, calculated birefringence for La3OSCl2[SbS3] is ∼0.269 at 2050 nm. In addition, the optical energy gap of 2.5 eV for La3OSCl2[SbS3] was derived, which can be assigned to the charge transition from the highest value of valence band derived dominantly from the of S 3p states to the lowest value of conduction band mainly made up of the Sb 5p and of La 5d states.