Crystal and electronic structure of the red semiconductor Ba4LaSbGe3Se13 comprising the complex anion [Ge2Se7-Sb2Se4-Ge2Se7]14-

Ba4LaGe3SbSe13 was prepared by reacting the elements under exclusion of air at 700degreesC, followed by slow cooling to room temperature. It crystallizes in a new type of the monoclinic space group P2(1)/c, with lattice dimensions of a= 1633.30(9) pm, b = 1251.15(7) put, c = 1303.21(7) pm, beta = 103.457(2)degrees, V = 2590.0(2) 10(6) pm(3) (Z = 4). The structure contains isolated GeSe4 as well as Ge2Se7 digermanate units. Two of the latter are interconnected via an Sb2Se4 bridge yielding an almost linear complex anion [Ge2Se7-Sb2Se4-Ge2Se7](14-). The oxidation states are assigned to be Ba-II, La-III, Ge-IV, Sb-III, and Se-II, in accord with an electronically saturated nonmetal. The lone pair of Sb-III reflects itself in highly irregular Se coordination. The red color of the material is indicative of semiconducting behavior with an activation energy of 2.0 eV. Electronic structure calculations based on the LMTO approximation point to a smaller gap, typical for this calculation method. We utilized the COHP tool to explore the bonding character of the different Sb-Se interactions. (C) 2004 Elsevier Inc. All rights reserved.