The Many Faces of Rare Earth Carbodiimide Compounds

Solid state metathesis reactions have been established as a successful tool in syntheses of rare earth carbodiimide compounds. Current results evidence the new compounds LiRE(CN2)(2) with RE = La, Ce and the carbodiimide nitride Ce-3(CN2)(3)N. LiRE(CN2)(2) compounds were synthesized by solid state metathesis reactions between REF3 and Li-2(CN2) in 1:2 molar ratio. Ce-3(CN2)(3)N was obtained by thermal conversion of LiCe(CN2)(2). Crystal structures of LiLa(CN2)(2) and Ce-3(CN2)(3)N were determined from X-ray single crystal data (LiLa(CN2)(2): P2(1)/m, a = 542.4(2) pm, b = 379.16(7) pm, c = 1013.0(3) pm, beta = 101.35(3)degrees; Ce-3(CN2)(3)N P2(1)2(1)2(1), a = 672.97(9) pm, b = 1309.8(2) pm, c = 1697.7(3) pm) and LiCe(CN2)(2) was assigned from indexed X-ray powder diffraction data (LiCe(CN2)(2): a = 541.9(1) pm, b = 374.50(8) pm, c = 1008.8(2) pm, beta = 101.21 (1)degrees). The crystal structure of LiLa(CN2)(2) represents a layer-like arrangement of ions as typical for this type of compounds. The crystal structure of Ce-3(CN2)(3)N reveals chains of [NCe4] tetrahedra running parallel to each other, and trigonal prismatic to trigonal antiprismatic arrangements of six distinctly interconnected [Ce-3-NCN-Ce-3] units. Both structures contain (CN2)(2-) ions deviating from their ideal D-infinity h symmetry, with C-N distances ranging between 121 and 126 pm and N-C-N angles near 180 degrees.