Vibrational and theoretical studies of urea and magnesium-urea complexes

The molecular structure and IR spectra of urea, H2NCONH2, in gas phase and in acetonitrile solution, as well as of the two complexes [MgU4Cl2] and [Mg U6]Cl-2 have been observed. The influence of environmental changes to geome try and spectra are shown. Various basis sets have been employed to safegua rd the validity of the reported findings, using polarization functions for all calculations to get the correct pyramidal amide configuration. The erro neous low energy of the C-2v symmetry group, after the addition of the ZPVE correction, is discussed. For the solvated urea molecule a reduction of th e energy barrier, compared to the gas phase urea, between the two minimum c onfigurations, C-2 and C-S, and the planar geometry, is observed. The lowes t energy minimum in acetonitrile is found to be the C-2 symmetry group, whi le for the two complexes, the local symmetry of urea is C-S or C-2 dependin g on the complex, or even on the coordination position of urea in the compl ex. The wagging motion of the amide group is also discussed in all the stud ied urea species. The computed geometries and most of the spectroscopic res ults are in good agreement with the available experimental data.