Matrix Isolation of Two Isomers of N₄CO

Abstract

Inorganic molecules containing polynitrogen chains are known as intrinsically unstable high-energetic compounds. Tetranitrogen (N 4 ) was merely detected as a gaseous metastable molecule with a lifetime of microseconds by neutralization-reionization mass spectrometry, [1] and only a few derivatives of N 4 with open-chain structures-N 4 O, [2] N 4 O 2 , [3] and [N 3 NFO][SbF 6 ] [4] -have been spectroscopically identified. A catenated pentanitrogen unit is found in the N 5 + ion.[5] Its structure and chemistry was recently explored by Christe et al., and the N 5 unit exhibits a bent structure with C 2v symmetry as shown by X-ray crystallography.Concerning the hexanitrogen compounds, numerous theoretical calculations have been devoted to the two isomers of N 6 , diazide and hexazine, but none of them were identified experimentally up to now. [6] To the contrary, its isoelectronic analogue, diisocyanate (OCN-NCO), was prepared by photolysis and flash pyrolysis of oxalic acid diazide, O 2 C 2 (N 3 ) 2 , and characterized by matrix IR spectroscopy. [7] Only the C 2h symmetrical conformer was computationally found to be a minimum, [8] and the initially formed nitrene intermediate was not observed. Our recent synthesis of pure carbonyl diazide, OC(N 3 ) 2 , [9] encouraged us to conduct a similar experiment in seeking azido isocyanate, N 3 -NCO, an even closer analogue to N 6 .Gaseous OC(N 3 ) 2 exhibits two broad absorptions at l max = 232 and 198 nm. Irradiation of Ar matrix-isolated OC(N 3 ) 2 with UV light (l = 255 nm, interference filter) was performed, and the appearance of new IR bands at the expense of those of OC(N 3 ) 2 was observed. Formation of CO was evidenced by a weak band at 2140.6 cm À1 ( Figure S1 in the Supporting Information), and strong new bands in the region of N 3 and NCO stretching modes appeared upon photolysis. To distinguish the different carriers of these bands, subsequent irradiation of the matrix with visible light (l ! 455 nm) was performed. No decomposition of OC(N 3 ) 2 was observed under these conditions, and the IR difference spectrum before and after l ! 455 nm photolysis is shown in Figure 1 b. The good agreement between the observed and calculated spectra (B3LYP/6-311 + G(3df), using a scaling factor of 0.9679) [10] for triplet N 3 C(O)N (Figure 1 a, Table 1) suggested its formation upon UV photolysis (l = 255 nm) of OC(N 3 ) 2 . The nitrene N 3 C(O)N was depleted upon visible irradiation (l ! 455 nm, Figure 1 b).In principle, two nitrene conformers can be formed which adopt a syn and anti orientation of the azide group with respect to the CÀN bond. In fact, weak satellites at 1602.6 cm À1 (Ar matrix) and 1602.9 cm À1 (Ne matrix) of the strong bands for the C=O stretching vibration at 1581.7 cm À1 (Ar matrix) and 1582.5 cm À1 (Ne matrix) might suggest the formation of a second nitrene conformer. However, the absence of any such features for the other nitrene bands indicates the presence of only one conformer. The preference for anti-N 3 C(O)N ( 3 A'') comes from various DFT calcul...

Toward Understanding the Decomposition of Carbonyl Diazide (N3)2C═O and Formation of Diazirinone cycl-N2CO: Experiment and Computations

“…10 A recent study of the photochemistry of (IV) in solid noble gas matrices showed that (IV) was quickly destroyed, producing N 2 and CO under visible irradiation. In contrast, ArF excimer laser (193 nm) irradiation caused transformation into the open-chain isomers ONCN, ONNC, and NOCN.…”

“…By contrast, the triplet ground state carbonyl nitrene intermediate 3 (II) has been obtained only by UV photolysis of (I) isolated in noble gas matrices. 10 The molecular structure of TS2 is similar to that of TS1, in the sense that one of the N 3 ligands is orientated nearly perpendicular to the O−C−N α plane. The most striking differences are related to the C−N α and N α −N β bond lengths ( Figure 6), and the ∠N α CN′ α bond angles.…”

“…Observed photolysis (blue) and thermal (red) decomposition routes starting from (N 3 ) 2 CO 6,9,10. Irradiation conditions used in photolysis experiments and temperatures at which the thermal decay occurs are indicated.…”

Das schwer fassbare Diazirinon, N2CO

“…[14] Selbst bei Pyrolysetemperaturen von 500 8C blieb etwas Diazid unzersetzt, und es wurden einige neue Banden beobachtet (Abbildung S3 in den Hintergrundinformationen). Durch Vergleich mit dem IR-Spektrum von cyclischem 1, das durch Berechnung anharmonischer Frequenzen auf dem CCSD(T)/ANO2-Niveau vorausgesagt wurde, ließen sich fast alle Banden der neuen Spezies zuordnen (Tabelle 1).…”

“…455 nm) ging das Nitren eine Curtius-Umlagerung zu dem N 6 -analogen N 3 -NCO ein. [14] Dieses N 3 -NCO zerfiel bei der Bestrahlung mit UV/Vis-Licht (l ! 335 nm) weiter in CO und N 2 .…”