Synthesis and characterization of Na5M(2+x)Sn(10-x) (x approximately = 0.5, M = Zn, Hg)--a doped tetrahedral framework structure.
Two homologous and isostructural compounds Na(5)M(2+x)Sn(10-x) (M = Zn, Hg) were obtained by direct reaction of the elements at high temperature. The crystal structures of these novel phases were determined from single-crystal X-ray diffraction data and represent a new structure type in tin chemistry. They crystallize in the space group Pbcn (No. 60, Z = 4) with a = 12.772(1), b = 10.804(1), and c = 12.777(1) A, V = 1763.1(2) A(3) for Na(5)Zn(2.28)Sn(9.72(2)) (I) and a = 12.958(1), b = 10.984(1), and c = 12.960(1) A, V = 1844.5(2) A(3) for Na(5)Hg(2.39)Sn(9.61(1)) (II). The structures consist of an anionic 3D open framework of tetrahedrally coordinated Sn and M atoms interwoven with a cationic 2D array of interconnected {NaNa(4)} tetrahedra. The framework can be partitioned into fragments of realgar-like units {Sn(8-x)M(x)}(2x-) and twice as many {Sn-M}(2-) dimers. Formally, the compounds are charge-balanced Zintl phases for x = 0.5. As the structure refinements lead to x = 0.28 and 0.39 for I and II, respectively, both structures are electron-rich and expected to be metallic. Theoretical investigations at the density functional theory level reveal a deep minimum at the Fermi level for x = 0.5. According to rigid band analyses, the electronic structure of the phases with the experimentally observed compositions corresponds to heavily doped semiconductors, thereby meeting an important requirement of thermoelectric materials.
Ponou
Siméon
S
Department Chemie der Technischen Universität Munchen, Lichtenbergstrasse 4, D-85747 Garching, Germany.
Kim
Sung-Jin
SJ
Fässler
Thomas F
TF