Bi12.86Ni4Br6 and Bi12.86Ni4I6: Subhalides with alternating intermetallic and salt-like layers

The reaction of bismuth and nickel with bromine or iodine at 730 K yields b lack, air insensitive, needle shaped crystals of the ternary subhalides Bi1 2.86Ni4X6 (X = Br, I). The isotypic compounds crystallize in the orthorhomb ic space groups Immm with a = 405.69(6) pm, b = 874.00(8) pm, c = 3744.7(4) pm for X = Br, and a = 410.05(5) pm, b = 912.84(7)pm, c = 3826.7(3)pm for X = I. The crystal structures contain characteristic fragments of the inter metallic phase Bi3Ni: chains consisting of face-sharing monocapped trigonal prisms of bismuth atoms with a nickel atom in the center of each prism. Th e chains form corrugated layers which are separated by halogen atoms and ol igomeric [BinX4n+2] units of varying length. The halogenobis-mutate(III) un its consist of trans-edge-sharing [BiX6] octahedra. They are disordered wit hin the crystal structures. The non-integer stoichiometric coefficients of Bi12.86Ni4X6 are due to the metric adjustment between the ionic and interme tallic parts of the structure. Extended Huckel calculations indicate, that the partial oxidation of the intermetallic phase causes a strengthening of the chemical bonding within the Bi3Ni chains. The subiodide Bi12.86Ni4I6 is paramagnetic and shows ferromagnetic ordering below 25 K.