Syntheses and crystal structures of trigonal rare-earth dioxymonocyanamides, Ln 2 O 2 CN 2 ( Ln =Dy, Ho, Er, Tm, Yb)

Trigonal rare-earth dioxymonocyanamides Ln 2 O 2 CN 2 ( Ln =Dy, Ho, Er, Tm, Yb) were synthesized by the modified solid-state metathesis (SSM) method, in which Ln 2 O 3 and melamine C 3 N 6 H 6 were mixed and heated at 850 °C in vacuumed silica ampoules. Possible chemical reaction pathways are proposed. X-ray diffraction (XRD) patterns of Ln 2 O 2 CN 2 were refined using the Rietveld method. Compounds Ln 2 O 2 CN 2 crystallize in the trigonal system with space group P 3 m 1, Z =1, and cell parameters of a and c varying from 3.7267(1) to 3.6407(1) Å and from 8.1848(3) to 8.1152(3) Å, respectively, as Ln atoms change from Dy to Yb. These compounds have stacking structures of Ln 2 O 2 2+ and CN 2 2− layers, similar to those of previously reported compounds Ln 2 O 2 CN 2 ( Ln =Ce, Pr, Nd, Sm, Eu, Gd). The presence of CN 2 2− ions has been confirmed by infrared spectroscopy, with two characteristic peaks in the vicinity of 651 and 2075 cm −1 .