Ammonothermal Synthesis of Alkali‐Alkaline Earth Metal and Alkali‐Rare Earth Metal Carbodiimides: K 5– x M x (CN 2 ) 2 +x (HCN 2 ) 1– x ( M = Sr, Eu) and Na 4.32 Sr 0.68 (CN 2 ) 2.68 (HCN 2 ) 0.32

Alkali‐alkaline earth metal and alkali‐rare earth metal carbodiimides, namely K 5– x M x (CN 2 ) 2+ x (HCN 2 ) 1– x ( x = 0 – 1) ( M = Sr, Eu) and Na 4.32 Sr 0.68 (CN 2 ) 2.68 (HCN 2 ) 0.32 , were synthesized under ammonothermal conditions in high‐pressure autoclaves. The structures of the three compounds can be derived from homeotypic K 5 H(CN 2 ) 3 and Na 5 H(CN 2 ) 3 by partial substitution of K + or Na + by Sr 2+ or Eu 2+ . The reactions were carried out in two step syntheses ( T 1 = 673 K, T 2 = 823 K) starting from sodium or potassium azide, dicyandiamide and strontium or Eu(NH 2 ) 2 , respectively. The crystal structures were solved and refined from single‐crystal X‐ray diffraction data [K 4.16 Sr 0.84 (CN 2 ) 2.84 (HCN 2 ) 0.16 : space group Im 3 m (no. 229), a = 7.8304(5) Å, Z = 2, R 1 = 0.024, wR 2 = 0.052; K 4.40 Eu 0.60 (CN 2 ) 2.60 (HCN 2 ) 0.40 : space group Im 3 m (no. 229), a = 7.8502(6) Å, Z = 2, R 1 = 0.022, wR 2 = 0.049]. In contrast to the potassium carbodiimides, the sodium‐strontium carbodiimide was only synthesized as microcrystalline powder. The crystal structure was determined by powder X‐ray diffraction and refined by the Rietveld method [Na 4.32 Sr 0.68 (CN 2 ) 2.68 (HCN 2 ) 0.32 : space group Im 3 m (no. 229), a = 7.2412(1) Å, Z = 2, R wp = 0.050]. The presence of hydrogencyanamide units ([HNCN] – ) next to carbodiimide units ([CN 2 ] 2– ) in all compounds was confirmed by FT‐IR spectroscopy.