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, [H3NH ċ NH3]⊕, was previously unknown. Single crystal X‐ray diffraction studies on NH4I · NH3 have shown that the interaction NH 4⊕ ċ NH3 leads to the formation of the cation N2H 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.
Trotz der großen Bedeutung der N–H…N‐Wasserstoffbrückenbindung in Chemie und Biochemie war die Struktur des einfachsten Systems mit dieser Bindung, [H3N‐H…NH3]⊕, im Festkörper bisher nicht bekannt. Einkristall‐Röntgenstrukturuntersuchungen an NH4I·NH3 haben gezeigt, daß die Wechselwirkung NH…NH3 zur Bildung des Kations N2H führt. Der durch Kleinste‐Quadrate‐Verfeinerung erhaltene N‐N‐Abstand beträgt 269(5) pm und ist damit etwas kleiner als der von Scheiner und Harding 1982 berechnete Gleichgewichtsabstand von 273.1 pm.
ChemInform Abstract NH4I•NH3 (I), prepared by exposure of NH4I to gaseous NH3 of 350-450 torr, crystallizes at 298 K in the cubic space group Pm3m with Z=1. The powder and single crystal XRD data confirm the presence of the title cation in (I). The N-N distance is determined to be 269 pm indicating a strong interaction between NH4+ and NH3. During cooling of (I), transitions to three other modifications with increasing degree of structural order are observed. (I) is tetragonal in the range 230-203 K (P4/mmm, Z=1) and transforms into an orthorhombic form (Z=2) at 203 K. The modification existing below 143 K is not identified. Cubic ND4I•ND3 directly transforms into the orthorhombic phase at 237 K.
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