Photo release of nitrous oxide from the hyponitrite ion studied by infrared spectroscopy. Evidence for the generation of a cobalt-N 2 O complex. Experimental and DFT calculations.

The solid state photolysis of sodium, silver and thallium hyponitrite (M2 N2 O2 , M=Na, Ag, Tl) salts and a binuclear complex of cobalt bridged by hyponitrite ([Co(NH3 )5 -N(O)-NO-Co(NH3 )5 ]4+ ) were studied by irradiation with visible and UV light in the electronic absorption region. The UV-visible spectra for free hyponitrite ion and binuclear complex of cobalt were interpreted in terms of Density Functional Theory calculations in order to explain photolysis behavior. The photolysis of each compound depends selectively on the irradiation wavelength. Irradiation with 340-460nm light and with the 488nm laser line generates photolysis only in silver and thallium hyponitrite salts, while 253.7nm light photolyzed all the studied compounds. Infrared spectroscopy was used to follow the photolysis process and to identify the generated products. Remarkably, gaseous N2 O was detected after photolysis in the infrared spectra of sodium, silver, and thallium hyponitrite KBr pellets. The spectra for [Co(NH3 )5 -N(O)-NO-Co(NH3 )5 ]4+ suggest that one cobalt ion remains bonded to N2 O from which the generation of a [(NH3 )5 CoNNO]+3 complex is inferred. Density Functional Theory (DFT) based calculations confirm the stability of this last complex and provide the theoretical data which are used in the interpretation of the electronic spectra of the hyponitrite ion and the cobalt binuclear complex and thus in the elucidation of their photolysis behavior. Carbonate ion is also detected after photolysis in all studied compounds, presumably due to the reaction of atmospheric CO2 with the microcrystal surface reaction products. Kinetic measurements for the photolysis of the binuclear complex suggest a first order law for the intensity decay of the hyponitrite IR bands and for the intensity increase in the N2 O generation. Predicted and experimental data are in very good agreement.