UNUSUAL BONDING IN TERNARY NITRIDES - PREPARATION, STRUCTURE AND PROPERTIES OF CE2MNN3

Ce2MnN3 was prepared by reaction of cerium nitride and manganese with nitrogen gas at 900 degrees C. It crystallizes isotypic to AC(2)MN(3) (Ac = U, Th; M = Cr, Mn) and Ce2CrN3, space group Immm (No. 71), a = 3 .74994(6)Angstrom, b = 3.44450(6)Angstrom and c = 12.4601(2)Angstrom. The manganese atoms are coordinated in a nearly square planar fashion by four nitrogen atoms. These corner-connected MnN4 units form infinit e (infinity) (1) [MnN2N2/2] chains, which run parallel to each other a long the crystallographic a-axis, forming the motif of hexagonal rod p acking. Cerium atoms connect the chains into a three-dimensional netwo rk. The results of measurements of the magnetic susceptibility, as wel l as of the electrical resistivity suggest metallic behavior. Electron ic effects leading to shorter bonds between manganese and bridging nit rogen atoms than between manganese and terminal nitrogen atoms in the (infinity) (1) [MnN2N2/2] chains were investigated through extended Hu ckel and LMTO band structure calculations. Issues pertaining to stabil ity of this and some other nitridometallate structures are discussed.