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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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Solid state metathesis reactions have been studied in fused silica tubes, by differential thermal analysis, and by X‐ray powder diffraction. A selection of reactions between metal (La, Nb, and Ni) chlorides and lithium nitride or lithium acetylide were investigated to get more insight into reaction pathways and intermediate reaction stages that may be adopted on course of the formation of metal nitrides or carbides. Intermediate compounds are considered to be important because they can control the reactivity of a system. Such compounds were traced by changing the molar ratios of reaction partners away from the salt‐balanced binary metal nitride or carbide target compositions. New preparative perspectives are discovered when metal chlorides were reacted with lithium nitridoborate or lithium cyanamide. Due to their reductive nature towards several d‐block metal chlorides, (BN2)3‐ and (CN2)2‐ react to form metals or metal nitrides plus X‐ray amorphous BN, and probably C3N4. With lanthanum chloride they can react to form nitridoborates and nitridocarbonates. The metathesis reaction between lithium cyanamide and cyanuric chloride (C3N3Cl3) instead of metal chloride was studied for the synthesis of C3N4.