On the Structure of the Cation N 2 H 7 ⊕ with an NH ċ N Hydrogen Bond in the Monoammonia Adduct of Ammonium Iodide

In spite of the great importance of the NH ċ N hydrogen bridge in chemistry and biochemistry, the solid‐state structure of the simplest system containing this bond, [H 3 NH ċ NH 3 ] ⊕ , was previously unknown. Single crystal X‐ray diffraction studies on NH 4 I · NH 3 have shown that the interaction NH   4 ⊕ċ NH 3 leads to the formation of the cation N 2 H   7 ⊕ . The N N distance determined by least squares refinement is 269(5) pm, somewhat shorter than the equilibrium distance of 273.1 pm calculated in 1982 by Scheiner and Harding .