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Keywords:

  • Beryllium;
  • Liquid ammonia;
  • Quantum chemistry;
  • Crystal structures;
  • X-ray diffraction;
  • Rietveld refinement

Abstract

Treatment of BeCl2 with dry liquid ND3 and subsequent removal of the solvent leads to the colourless microcrystalline powder of [Be(ND3)4]Cl2. It crystallises in the orthorhombic space group Pna21 with a = 9.395(4), b = 11.901(6), c = 6.761(3) Å, V = 755.9(6) and Z = 4 at 27 °C, and a = 9.3736(8), b = 11.8162(12), c = 6.6596(6) Å, V = 737.62(12) and Z = 4 at –269.6 °C. The structure contains the tetrahedral tetraammineberyllium(II) cation which follows the octet rule. It was shown to be stable under ambient conditions and temperatures up to approximately 175 °C. We additionally discuss the aid of solid-state quantum chemical calculations for the assignment of proper crystallographic space groups in cases where the choice between centrosymmetry and noncentrosymmetry is not completely obvious, e.g. here between Pna21 and Pnma. Thermogravimetric measurements show that [Be(ND3)4]Cl2 decomposes only above approximately 175 °C, giving off two equivalents of ND3 to form [Be(ND3)2Cl2]. The latter seems to be stable up to approximately 300 °C after which it sublimes. These results show unambiguous evidence for the stability of the tetraammineberyllium(II) cations of the title compounds from –269.6 °C to 175 °C.