Syntheses, Crystal and Electronic Structures, and Physical Properties of Quaternary Semiconductors: Ln₂Mn₃Sb₄S₁₂ (Ln = Pr, Nd, Sm, Gd)

Four new quaternary lanthanide antimony sulfides: Ln₂Mn₃Sb₄S₁₂ (Ln = Pr, Nd, Sm, Gd) have been synthesized from a stoichiometric element mixture at 1373 K by conventional solid state reactions. These compounds crystallize in the monoclinic space group C2/m with the unit cell parameters of a = 19.928(2)−19.9672(6) Å, b = 3.9323(4)−3.8803(2) Å, c = 14.921(2)−14.9011(1) Å, V = 938.5(2)−925.63(6) ų, and Z = 2 on going from Ln = Pr to Gd. Their structure represents a novel wavy MnS₆ octahedron layer decorated on both sides by chains of an SbS₅ square pyramid via strong Sb−S bonding interactions (< 3.0 Å). Such a MnS₆ octahedron layer consists of chains of an edge-sharing [Mn1S₆]₂ dimer extending along [010] that are interconnected by single strings of an edge-sharing Mn2S₆ octahedron at axial S apexes. Sm₂Mn₃Sb₄S₁₂ displays spin-canted antiferromagnetic interactions between Sm²⁺ and Mn²⁺ centers and an optical gap of 1.50 eV. The DFT study indicates an indirect band gap with an electronic transfer excitation of S 3p to Sb 5p orbital electrons.