Crystalline samples of rare earth carbodiimides were synthesized by solid-state metathesis reactions of rare earth trichlorides with lithium cyanamide in sealed silica ampules. Two distinct structures were determined by single-crystal X-ray diffraction. The structure determined for Sm2(CN2)3 [C2/m, Z = 2, a = 14.534(2) A, b = 3.8880(8) A, c = 5.2691(9) A, beta = 95.96(2) degrees , R1 = 0.0267, and wR2 = 0.0667] was assigned for RE2(CN2)3 compounds with RE = Y, Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er, and the structure determined for Lu2(CN2)3 [R32, Z = 3, a = 6.2732(8) A, c = 14.681(2) A, R1 = 0.0208, and wR2 = 0.0526] was assigned for the smallest rare earth ions with RE = Tm, Yb, and Lu by powder X-ray diffraction. Both types of crystal structures are characterized by layers of [NCN](2-) ions whose arrangements can be derived from the motif of a closest packed layer of sticks. These layers alternate with layers of rare earth ions in a one-by-one sequence. Different tilting arrangements of the N-C-N-axes relative to the stacking directions (c) and different arrangements of RE3+ ions within metal atom layers account for the two distinct structures in which Sm3+ and Lu3+ ions adopt the coordination numbers 7 and 6, respectively.

Solid state metathesis reactions between LaCl3 and Li2(CN2) carried out in silica ampoules at 600 °C over two days resulted in the formation of a light gray powder, later identified to be lanthanum chloride cyanamide. Single crystals were obtained as colourless transparent plates using a LiCl‐KCl flux. The crystal structure of LaCl(CN2) was solved and refined from X‐ray single crystal data (P21/m (no. 11), Z = 2, a = 5.330(1) Å, b = 4.0305(8) Å, c = 7.545(1) Å, V = 159.24(5) Å3, β = 100.75(2)°). The structure of LaCl(CN2) is closely related to the tetragonal LaOCl (PbFCl type) structure and contains a [La2Cl2]4+ block layer and two layers of (CN2)2‐ ions in an alternating sequence. The La3+ ion in LaCl(CN2) is situated in a polyhedron composed of four chloride ions on one side and five cyanamide ions on the other side. Cerium and praseodymium analogues were identified from indexed powder patterns with analogous unit cells, assuming them to form isostructural compounds.

M[B(CN)4]2: Two new Tetracyanoborate Compounds with divalent Cations (M = Zn, Cu)The reaction of ZnO or CuO with [H3O][B(CN)4] in aqueous solution yielded single crystals of Zn[B(CN)4]2 and Cu[B(CN)4]2, respectively. The compounds were characterized by single‐crystal X‐ray diffraction. Zn[B(CN)4]2 ($P{\bar 3}m{\rm 1}$ (no. 164), a = b = 7.5092(9) Å, c = 6.0159(6) Å, Z = 1) crystallizes isotypic with Hg[B(CN)4]2. The structure of Cu[B(CN)4]2 (C2/m (no. 12), a = 13.185(3) Å, b = 7.2919(9) Å, c = 6.029(1) Å, β = 93.02(2)°, Z = 2) can be considered as a super‐structure, resulting from Jahn‐Teller distortion of the Cu2+ ions. Magnetic measurements were performed for the copper compound. Vibrational spectra and thermal stabilities were compared with the known mercury(II) tetracyanoborate.

The new carbodiimide compounds LaF(CN2) and LiPr2F3(CN2)2 were obtained as crystalline powders by solid‐state metathesis reactions from 1:1 molar ratios of REF3 (RE = rare earth) and Li2(CN2) at temperatures between 500 and 700 °C over 4 days in fused copper ampoules. Higher proportions of Li2(CN2) in reactions yielded RE2(CN2)3 compounds, including the new Eu2(CN2)3. Single‐crystal structure refinements were performed for LaF(CN2) and LiPr2F3(CN2)2. Homologous LiRE2F3(CN2)2 compounds with RE = Ce, Pr, Nd, Sm, Eu, Gd were assigned by isotypic indexing of their XRD patterns. The crystal structure of LaF(CN2) contains planar [La3F3] layers being interconnected by carbodiimide ions, and is related with that of the mineral bastnäsite (REF(CO3)).

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