Unusual Bonding in Ternary Nitrides: Preparation, Structure and Properties of Ce₂MnN₃.

Abstract

Ce 2 MnN 3 was prepared by reaction of cerium nitride and manganese with nitrogen gas at 900 °C. It crystallizes isotypic to AC 2 MN 3 (Ac = U, Th; M = Cr, Mn) and Ce 2 CrN 3 , space group Immm (No. 71), a = 3.74994(6) Å, b = 3.44450(6) Å and c = 12.4601(2) Å. The manganese atoms are coordinated in a nearly square planar fashion by four nitrogen atoms. These corner-connected MnN 4 units form infinite 1 ∞ [MnN 2 N 2/2 ] chains, which run parallel to each other along the crystallographic a-axis, forming the motif of hexagonal rod packing. Cerium atoms connect the chains into a three-dimensional network. The results of measurements of the magnetic susceptibility, as well as of the electrical resistivity suggest metallic behavior. Electronic effects leading to shorter bonds between manganese and bridging nitrogen atoms than between manganese and terminal nitrogen atoms in the 1 ∞ [MnN 2 N 2/2 ] chains were investigated through extended Hückel and LMTO band structure calculations. Issues pertaining to stability of this and some other nitridometallate structures are discussed.