Synthesis and structure of Ba₈Cu₃In₄N₅ with nitridocuprate groups and one-dimensional infinite indium clusters

Single crystals of the quaternary compound Ba₈Cu₃In₄N₅ were prepared by heating Ba, Cu, and In in a Na flux at 1023 K under 7 MPa of N₂, and by slow cooling from this temperature. The crystal structure was analyzed by single-crystal X-ray diffraction. It crystallizes in an orthorhombic cell (space group Immm (No. 71), Z=2) with a=4.0781(6), b=12.588(2), and c = 19.804(3) Å at 298 K. The structural formula is expressed as Ba₈[CuN₂]₂[CuN]In₄. Nitridocuprates of one-dimensional chains ∞¹[CuN_2/2] and isolated units ⁰[CuN₂], and one-dimensional indium clusters ∞¹[In₂In_4/2] are contained in the structure. A split-site model applied for the arrangement of ∞¹[CuN_2/2] chains suggested that there is a short-bond, long-bond alternation of the Cu-N bondings. The electrical resistivity of Ba₈Cu₃In₄N₅ was 3.44 mΩ·cm at 298 K. A metallic temperature dependence of the resistivity was observed down to 10 K.