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 Li RE (CN 2 ) 2 with RE = La, Ce and the carbodiimide nitride Ce 3 (CN 2 ) 3 N. Li RE (CN 2 ) 2 compounds were synthesized by solid state metathesis reactions between RE F 3 and Li 2 (CN 2 ) in 1:2 molar ratio. Ce 3 (CN 2 ) 3 N was obtained by thermal conversion of LiCe(CN 2 ) 2 ., Crystal structures of LiLa(CN 2 ) 2 and Ce 3 (CN 2 ) 3 N were determined from X‐ray single crystal data (LiLa(CN 2 ) 2 : P 2 1 / m , a = 542.4(2) pm, b = 379.16(7) pm, c = 1013.0(3) pm, β = 101.35(3) °; Ce 3 (CN 2 ) 3 N: P 2 1 2 1 2 1 , a = 672.97(9) pm, b = 1309.8(2) pm, c = 1697.7(3) pm) and LiCe(CN 2 ) 2 was assigned from indexed X‐ray powder diffraction data (LiCe(CN 2 ) 2 : a = 541.9(1) pm, b = 374.50(8) pm, c = 1008.8(2) pm, β = 101.21(1) °)., The crystal structure of LiLa(CN 2 ) 2 represents a layer‐like arrangement of ions as typical for this type of compounds. The crystal structure of Ce 3 (CN 2 ) 3 N reveals chains of [NCe 4 ] 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 (CN 2 ) 2– ions deviating from their ideal D ∞h symmetry, with C–N distances ranging between 121 and 126 pm and N–C–N angles near 180°.