THE AMINODIAZONIUM CATION, H2N3+

The H2N3+ salts of SbF6-, AsF6-, and BF4- have been prepared and, for the first time, been isolated from HF solutions of HN3 and the corresponding Lewis acids. They are hygroscopic white solids which are stable at room temperature. The crystal structure of H2N3+SbF6- was determined at 20 K. This compound crystallizes in the orthorhombic system, space group Pmc2(1), with two molecules in a unit cell of dimensions a = 5.794 (3) angstrom, b = 5.113 (2) angstrom, and c = 9.919 (5) angstrom with R = 0.015, R(w) = 0.022, for 587 observed [I > 3sigma(I)] reflections. In addition to two almost perfectly octahedral SbF6- anions, the unit cell contains two asymmetric H2N3+ cations with N(1)-N(2) = 1.295 (5) angstrom, N(2)-N(3) = 1.101 (6) angstrom, and N(1)-N(2)-N(3) = 175.3 (5)degrees and both hydrogens bonded to the same nitrogen atom, N(1). The infrared and Raman spectra of these salts were also recorded. Local density functional calculations were carried out for H2N3+ and isoelectronic H2NCN and used for the assignment of the observed vibrational spectra and the determination of their force fields. The general agreement between the calculated and observed geometries and frequencies is very good. The results from the LDF calculations indicate that the H2N group in H2N3+ is less pyramidal than that in H2NCN and, therefore, possesses a lower inversion energy barrier.