Crystal Structure of the Ammine Complex [Ca(C ₂ H) ₂ (NH ₃ ) ₄ ]

[Ca(C 2 H) 2 (NH 3 ) 4 ] was obtained by reaction of elemental calcium dissolved in liquid ammonia with acetylene (C 2 H 2 ). Slow evaporation of the ammonia led to the formation of needle‐shaped crystals of the product, which degrade easily at room temperature, releasing NH 3 . Single crystals suitable for an X‐ray single‐crystal structure analysis were isolated directly from the ammonia mother liquor at low temperatures. [Ca(C 2 H) 2 (NH 3 ) 4 ] crystallizes in the orthorhombic space group Pnma (no. 62) with Z = 4. Isolated [Ca(C 2 H) 2 (NH 3 ) 4 ] complexes with four NH 3 ligands forming the square plane and two end‐on coordinating C 2 H − anions at the trans apices of an octahedral coordination sphere are interconnected in the crystal structure via weak NH … N hydrogen bonds. Attempts to convert [Ca(C 2 H) 2 (NH 3 ) 4 ] into CaC 2 by heating have not been successful up to now.