NEW STRUCTURE TYPE IN THE BA-IN-CU-SYSTEM

Gerlinde Frenzen

FB Chemie-Biologie, Universität Kassel, D-34109 Kassel
email: frenzen@fkc-ws1.chemie.uni-kassel.de

Keywords: Intermetallic Compound, Crystal Structure, Electronic Structure

Investigation of the system Ba-In-Cu revealed the new compound Ba₆In₇Cu₂ . Crystals of the compound are prepared by reaction of the elements in sealed steel tubes at 1000°C and subsequent annealing at 600°C. Ba₆In₇Cu₂ crystallizes in the trigonal space group
R with the cell dimensions: a = 1491.6(4), c = 743.2(2) pm, Z = 3. The structure consists of linear chains of In₇Cu₂ cubes, connected by direct bonds between vertices. Cu occupies the centers of the cubes, the occupation of the bridging vertices is disordered with 50% copper and 50 % indium. The bond lengths for the indium atoms are: 274.1(1) pm to the central copper atom, 305.3(1) pm to the bridging vertex and 2 x 314.2(1) pm to the other indium vertices. The cube is slightly distorted: distance copper - bridging vertex: 249.9(2) pm (2x), Cu - In: 274.1(1) pm (6x). The distance between the bridging vertices is
243.5(3) pm, they are surrounded by three Ba atoms in the remarkably short distance of 338.4(1) pm. The chemical bonding is discussed with semiempirical band structure and COOP calculations.