FE(N2)N (N = 1-5): STRUCTURE, BONDING, AND VIBRATIONS FROM DENSITY FUNCTIONAL THEORY

The Fe(N2)n (n = 1−5) complexes have been studied with the LCGTO-KS-DF method. The structures containing end-on and side-on N2 ligands have been fully optimized and the dissociation energies estimated. The ground states are predicted to be end-on complexes with the exception of n = 2. The vibrational analysis of all predicted ground states is reported. The effect of 15N isotopic substitution on the vibrational frequencies has been estimated. Comparisons are made with the isoelectronic species Fe(CO)n. The Fe−N2 bonding has been discussed in terms of σ donation and π back-donation and the Mulliken population analysis. The predicted harmonic frequencies show that the infrared spectra of Fe(N2)4 and Fe(N2)5 are similar, and the two complexes could not be distinguished in nitrogen matrix experiments using infrared spectroscopy.