title: Superspace description of the modulated structure of the metal-salt-hybrid Bi(7-delta)Ni2Br(5-2delta) (delta = 1/9).
abstract: The compound Bi(7-delta)Ni2Br(5-2delta) = (Bi3Ni)2[Bi(1-delta)Br4]Br(1-2delta) (delta = 1/9) is a sub-bromide of the intermetallic phase Bi3Ni. Its crystal structure contains metallic rods, 1infinity[Bi3Ni], which are embedded in a salt-like matrix of bromido-bismuthate(III) and bromide anions. The non-stoichiometry originates from the variation of the number n of trans edge-sharing octahedra in the [Bi(n)Br(4n + 2)]((n + 2)-) oligomers (3 < or = n < or = 5), as well as from vacancies on the sites of the isolated Br atoms. The simplified structure is described in the orthorhombic space group Cmcm with a = 4.0660 (4), b = 23.305 (3), c = 17.130 (2) A. It shows a statistical distribution of vacancies and orientational disorder of the concatenated octahedra. By choosing the modulation vector q = a*/9 + b*/2, the additional weak reflections of the diffraction pattern can be indexed. In the [3 + 1]-dimensional superspace group Pmnm(alpha(1/2)0)000, an ordered structure model is achieved. The modulated crystal structure bears a strong resemblance to the somewhat higher oxidized sub-bromide Bi(7-delta)Ni2Br5 (delta = 1/9).
authors.affiliation: Inorganic Chemistry, Department of Chemistry and Food Chemistry, Dresden University of Technology, D-01062 Dresden, Germany.
authors.forename: B
authors.initials: B
authors.lastname: Wahl
authors.forename: M
authors.initials: M
authors.lastname: Ruck