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Mallmann, Mathias; Häusler, Jonas; Cordes, Niklas; Schnick, Wolfgang (2017): 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). In: Zeitschrift für Anorganische und Allgemeine Chemie, Vol. 643, No. 23: pp. 1956-1961
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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)(3) and Na5H(CN2)(3) by partial substitution of K+ or Na(+)by Sr2+ or Eu2+. 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(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 group Im (3) over barm (no. 229), a = 7.8304(5) angstrom, Z = 2, R-1 = 0.024, wR(2) = 0.052;K4.40Eu0.60(CN2)(2.60)(HCN2)(0.40): space group Im (3) over barm (no. 229), a = 7.8502(6) angstrom, 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 [Na4.32Sr0.68(CN2)(2.68)(HCN2)(0.32): space group Im (3) over barm (no. 229), a = 7.2412(1) angstrom, Z = 2, R-wp = 0.050]. The presence of hydrogencyanamide units ([HNCN](-)) next to carbodiimide units ([CN2](2-)) in all compounds was confirmed by FT-IR spectroscopy.