The Raman and IR vibration modes of metal pentazolate hydrates [Na(H 2 O)(N 5 )]·2H 2 O and [Mg(H 2 O) 6 (N 5 ) 2 ]·4H 2 O.

The detailed illustrations of the structures, elastic properties, and Raman and IR vibration modes for [Na(H ₂ O)(N ₅ )]·2H ₂ O (a) and [Mg(H ₂ O) ₆ (N ₅ ) ₂ ]·4H ₂ O (b) have been presented in this investigation by using the first-principles method based on the density functional theory. Our results indicate that the active centers of both two types of the energetic metal pentazolate hydrates appear on the cyclo-N ₅ . The bonding character of N atoms in the cyclo-N ₅ is shown to be covalent, and the cyclo-N ₅ ring can be considered as an anion. Based on the analysis of elastic properties, we conclude that complex a is easier to deform than b, and both complexes are mechanically stable. From the calculated Raman and IR vibration modes, the vibration in the region of 960-1206 cm ^-1 (for a) and 985-1208 cm ^-1 (for b) is determined by basically mixing the cyclo-N ₅ stretching and deformation modes. The vibrational modes of a and b in their highest frequency zones are both related to the stretching of the O-H bonds.