Ammonothermal Synthesis of Alkali‐Alkaline Earth Metal and Alkali‐Rare Earth Metal Carbodiimides: K5–xMx(CN2)2+x(HCN2)1–x(M= Sr, Eu) and Na4.32Sr0.68(CN2)2.68(HCN2)0.32

Abstract

Alkali‐alkaline earth metal and alkali‐rare earth metal carbodiimides, namely K5–xMx(CN2)2+x(HCN2)1–x(x= 0 – 1) (M= Sr, Eu) and Na4.32Sr0.68(CN2)2.68(HCN2)0.32, were synthesized under ammonothermal conditions in high‐pressure autoclaves. The structures of the three compounds can be derived from homeotypic K5H(CN2)3and Na5H(CN2)3by partial substitution of K+or Na+by Sr2+or Eu2+. The reactions were carried out in two step syntheses (T1= 673 K,T2= 823 K) starting from sodium or potassium azide, dicyandiamide and strontium or Eu(NH2)2, respectively. The crystal structures were solved and refined from single‐crystal X‐ray diffraction data [K4.16Sr0.84(CN2)2.84(HCN2)0.16: space groupIm3m(no. 229),a= 7.8304(5) Å,Z= 2,R1= 0.024,wR2= 0.052; K4.40Eu0.60(CN2)2.60(HCN2)0.40: space groupIm3m(no. 229),a= 7.8502(6) Å,Z= 2,R1= 0.022,wR2= 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 [Na4.32Sr0.68(CN2)2.68(HCN2)0.32: space groupIm3m(no. 229),a= 7.2412(1) Å,Z= 2,Rwp= 0.050]. The presence of hydrogencyanamide units ([HNCN]–) next to carbodiimide units ([CN2]2–) in all compounds was confirmed by FT‐IR spectroscopy.