科研之友
微信
新浪微博
Facebook
分享链接
摘要
Five new isotypic quaternary chalcogenides containing rare-earth metal atoms crystallizing in the hexagonal noncentrosymmetric space group P6(3) (No. 173) with the La3CuSiS7 structure type have been synthesized by reacting the appropriate anhydrous rare-earth trichloride with sodium thiogermanate, Na2GeS3. The reaction between LnCl(3) and Na2GeS3 in an evacuated fused-silica ampule produced high yields of good-quality crystals of NaLn(3)GeS(7) [Ln = Ce (I), Nd (II), Sm (III), Gd (IV), and Yb (V)], while a similar reaction between EuCl3 and Na2GeS3 yielded a quinary chloride thiogermanate, Na1.2Eu3.4Cl2Ge3S9 (VI), incorporating a cyclic trimeric Ge(3)S9 building unit and adopting a structure related to La3CuSiS7. The crystal structure of the compounds comprises a complex network of bicapped trigonal-prismatic LnS(8) and GeS4 tetrahedra, which creates channels along the [001] direction. The Na+ cations reside in these channels within trigonally distorted octahedral coordination environments, surrounded by six S atoms. For compounds III-V, the temperature dependence of the magnetic susceptibility indicates that these compounds are paramagnetic with mu(eff) = 1.86, 8.01, and 3.87 mu(B), for III-V, respectively. The experimental mu(eff) for IV is close to the theoretical value of 7.94 for free Gd3+ ions, while mu(eff) values for III and V deviate from their theoretical values of 0.86 and 4.54 mu(B) for Sm3+ and Yb3+ ions, respectively. These compounds are semiconductors with optical band gaps of around 1.3 eV for III and V. Extended Huckel calculations suggest that the valence band comprises primarily S 3p and the bottom of the conduction band is dominated by empty rare-earth 5d orbitals. Compound VI exhibits a sharp optical absorption of around 2.18 eV, which is attributed to the f -> d transition of Eu-II. The effective magnetic moment of 7.94 mu(B)/Eu is in excellent agreement with the theoretical value of 7.94 mu(B) for the free Eu2+ ion.
- 出版日期2015-2-2
