Synthesis, crystal structures, magnetic and electric transport properties of Eu11InSb9 and Yb11InSb9

Two new rare-earth metal containing Zintl phases, Eu11InSb9 and Yb11InSb9 have been synthesized by reactions of the corresponding elements in molten In metal to serve as a self-flux. Their crystal structures have been determined by single crystal X-ray diffraction-both compounds are isostructural and crystallize in the orthorhombic space group Iba2 (No. 45), Z = 4 with unit cell parameters a = 12.224(2) angstrom, b = 12.874(2) angstrom, c = 17.315(3)angstrom for Eu11InSb9, and a = 11.7886(11) angstrom, b = 12.4151(12)angstrom, c = 16.6743(15)angstrom for Yb11InSb9, respectively (Ca11Sb9-type, Pearson's code o/84). Both structures can be rationalized using the classic Zintl rules, and are best described in terms of discrete In-centered tetrahedra of Sb, [InSb4](9-), isolated Sb dimers, [Sb-2](4-), and isolated Sb anions, Sb3-. These anionic species are separated by Eu2+ and Yb2+ cations, which occupy the empty space between them and counterbalance the formal charges. Temperature-dependent magnetic susceptibility and resistivity measurements corroborate such analysis and indicate divalent Eu and Yb, as well as poorly metallic behavior for both Eu11InSb(9) and Yb(11)InSb9. The close relationships between these structures and those of the monoclinic alpha-Ca21Mn4Sb18 and Ca21Mn4Sb18 are also discussed. (c) 2007 Elsevier Inc. All rights reserved.