An X-ray study at 298 and 120 K of the strong, symmetrical NHN bond in hydrogen diquinuclidin-3-one perchlorate

Abstract

The effect of temperature on the NHN hydrogen bond in bis(quinuclidin-3-one)hydrogen(1+) perchlorate has been investigated by X-ray diffraction. The N ⋯ N distance has been found to be 2.648(9)Å at 298 K and 2.629(4)Å at 120 K. The splitting of the electron density at room temperature has been interpreted as indicating an asymmetric location for hydrogen. At 120 K the bond becomes more symmetrical, probably due to bridge shortening. The type of potential governing the proton motion is discussed and it is proposed that an energy barrier may develop during high-amplitude low-frequency hydrogen-bond vibrations.