Abstract
AbstractRbNb4Br11 was obtained by a solid state reaction of niobium powder, NbBr5 and RbBr in a sealed niobium tube at 500 °C. It crystallizes in the orthorhombic space group Pmma with a = 1699.5(1), b = 726.7(1), c = 694.5(1) pm, V = 857.6(1)·106 pm3, Z = 2 and is isotypic with CsNb4Br11. Four niobium atoms build a cluster in the shape of a rhombus with bonding distances of 295 pm (Nb1–Nb2) and 304 pm (Nb2–Nb2), respectively. The structure consists of [{Nb4}Br6iBr10/2a–a]–cluster complex anions that are interconnected by two common edges and two faces to the next cluster complexes, thus forming a 2D undulated layer structure. The Rb+ ion is coordinated by 12 Br– ions in the shape of an anticuboctahedron. Electronic structure calculations indicate the presence of a band gap of approximately 0.33 eV. This is experimentally confirmed by an electrical conductivity measurement revealing a slightly higher gap of 0.46 eV.
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