Complexation of formaldoxime and acetaldoxime with nitrogen

The complexes formed between formaldoxime (FNOH) or Z- and E-acetaldoxime (Z-AcNOH, E-AcNOH) and nitrogen have been studied by FTIR matrix isolation spectroscopy and by ab initio MP2/6-311++G(2d, 2p) calculations. The calculations showed the stability of seven structures for the 1:1 FNOH···N2, Z-AcNOH···N2 and E-AcNOH···N2 complexes; the most stable of the seven structures is that with the N2 attached to the OH group of the oxime. The stability of the corresponding complexes is in the following energetic order: E (FNOH···N2) < E (E-AcNOH···N2) < E (Z-AcNOH···N2). The FTIR spectra evidence that in the argon matrices the most stable 1:1 structures are present. The spectra indicate also the formation of the other structures for these systems however their concentration is much lower than the concentrations of the most stable complexes. The quantitative spectra analysis demonstrated that Z-AcOH···N2 complexes are more readily formed than the E-AcOH···N2 ones indicating the higher acidity of the first isomer with respect to the second one. In the matrices with larger concentration of nitrogen the 1:2 formaldoxime-nitrogen complex was also identified and its structure is discussed on the basis of theoretical spectra calculated for the eleven optimized FNOH···(N2) structures.