Syntheses, Crystal and Electronic Structures, and Physical Properties of Quaternary Semiconductors: Ln<sub>2</sub>Mn<sub>3</sub>Sb<sub>4</sub>S<sub>12</sub> (Ln = Pr, Nd, Sm, Gd)

Four new quaternary lanthanide antimony sulfides: Ln<sub>2</sub>Mn<sub>3</sub>Sb<sub>4</sub>S<sub>12</sub> (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 <i>C2/m</i> with the unit cell parameters of <i>a</i> = 19.928(2)−19.9672(6) Å, <i>b</i> = 3.9323(4)−3.8803(2) Å, <i>c</i> = 14.921(2)−14.9011(1) Å, <i>V</i> = 938.5(2)−925.63(6) Å<sup>3</sup>, and <i>Z</i> = 2 on going from Ln = Pr to Gd. Their structure represents a novel wavy MnS<sub>6</sub> octahedron layer decorated on both sides by chains of an SbS<sub>5</sub> square pyramid via strong Sb−S bonding interactions (< 3.0 Å). Such a MnS<sub>6</sub> octahedron layer consists of chains of an edge-sharing [Mn1S<sub>6</sub>]<sub>2</sub> dimer extending along [010] that are interconnected by single strings of an edge-sharing Mn2S<sub>6</sub> octahedron at axial S apexes. Sm<sub>2</sub>Mn<sub>3</sub>Sb<sub>4</sub>S<sub>12</sub> displays spin-canted antiferromagnetic interactions between Sm<sup>2+</sup> and Mn<sup>2+</sup> 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.