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

Four new quaternary lanthanide antimony sulfides: Ln(2)Mn(3)Sb(4)S(12) (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) angstrom, b= 3.9323(4)-3.8803(2) angstrom, c= 14.921(2)-14.9011(1) angstrom, V= 938.5(2)-925.63(6) angstrom(3), 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 angstrom). Such a MnS6 octahedron layer consists of chains of an edge-sharing [Mn1S(6)](2) dimer extending along [010] that are interconnected by single strings of an edge-sharing Mn2S(6) 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.