Bi12,86Ni4Br6 und Bi12,86Ni4I6: Subhalogenide mit intermetallischen und salzartigen Schichtpaketen in alternierender Abfolge

Bi_12.86Ni₄Br₆ and Bi_12.86Ni₄I₆: Subhalides with Alternating Intermetallic and Salt‐like Layers The reaction of bismuth and nickel with bromine or iodine at 730 K yields black, air insensitive, needle shaped crystals of the ternary subhalides Bi_12.86Ni₄X₆ (X = Br, I). The isotypic compounds crystallize in the orthorhombic 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 intermetallic phase Bi₃Ni: chains consisting of face‐sharing mono‐capped trigonal prisms of bismuth atoms with a nickel atom in the center of each prism. The chains form corrugated layers which are separated by halogen atoms and oligomeric Bi_nX_4n+2] units of varying length. The halogenobismutate(III) units consist of trans‐edge‐sharing BiX₆] octahedra. They are disordered within the crystal structures. The non‐integer stoichiometric coefficients of Bi_12.86Ni₄X₆ are due to the metric adjustment between the ionic and intermetallic parts of the structure. Extended Hückel calculations indicate, that the partial oxidation of the intermetallic phase causes a strengthening of the chemical bonding within the Bi₃Ni chains. The subiodide Bi_12.86Ni₄I₆ is paramagnetic and shows ferromagnetic ordering below 25 K.