The dinitramide anion, N(NO2)(2)(-)

The infrared and Raman spectra of the NH4+, K+, and Cs+ salts of N(NO2)(2)(-) in the solid state and in solution have been measured and are assigned with the help of ab initio calculations at the HF/6-31G* and MP2/6-31+G* levels of theory. In agreement with the variations observed in the crystal structures, the vibrational spectra of the N(NO2)(2)(-) anion are also strongly influenced by the counterions and the physical state. Whereas the ab initio calculations for the free N(NO2)(2)(-) ion indicate a minimum energy structure of C-2 symmetry, Raman polarization measurements on solutions of the N(NO2)(2)(-) anion suggest point group C-1 (i.e., no symmetry). This is attributed to the very small (<3 kcal/mol) N-NO2 rotational barrier in N(NO2)(2)(-) which allows for easy deformation.