Dinitrogen trioxide


Dinitrogen trioxide is the chemical compound with the formula N2O3. This deep blue solid is one of the simple nitrogen oxides. It forms upon mixing equal parts of nitric oxide and nitrogen dioxide and cooling the mixture below −21 °C :
Dinitrogen trioxide is only isolable at low temperatures, i.e. in the liquid and solid phases. At higher temperatures the equilibrium favors the constituent gases, with Kdiss = 193 kPa.
This compound is sometimes called "nitrogen trioxide", but this name properly refers to another compound, the nitrate radical

Structure and bonding

Typically, N–N bonds are similar in length to that in hydrazine. Dinitrogen trioxide, however, has an unusually long N–N bond at 186 pm. Some other nitrogen oxides also possess long N–N bonds, including dinitrogen tetroxide. The N2O3 molecule is planar and exhibits Cs symmetry. The dimensions displayed below come from microwave spectroscopy of low-temperature, gaseous N2O3:


It is the anhydride of the unstable nitrous acid, and produces it when mixed into water. An alternative structure might be anticipated for the true anhydride, i.e. O=N–O–N=O, but this isomer is not observed. If the nitrous acid is not then used up quickly, it decomposes into nitric oxide and nitric acid. Nitrite salts are sometimes produced by adding N2O3 to solutions of bases: