A DENSITY-FUNCTIONAL STUDY OF FE-N-2, FE-N-2(-N-2(-)() AND FE)

The interaction of an iron atom with molecular nitrogen was studied us ing density functional theory. Calculations were of the all-electron t ype and both conventional local and gradient-dependent models were use d. A ground state of linear structure was found for Fe-N-2, with 2S 1 = 3, whereas the triangular Fe-N-2 geometry, of C-2v symmetry, was l ocated 2.1 kcal/mol higher in energy, at least for the gradient-depend ent model. The reversed order was found using the conventional local a pproximation. In Fe-N-2, the N-N bond is strongly perturbed by the iro n atom: It has a bond order of 2.4, a vibrational frequency of 1886 cm (-1), and an equilibrium bond length of 1.16 Angstrom. These values ar e 3.0, 2359 cm(-1), and 1.095 Angstrom, respectively, for the free N-2 molecule. With the gradient-dependent model and corrections for nonsp hericity of the Fe atom, a very small binding energy, 8.8 kcal/mol, wa s calculated for Fe-N-2. Quartet ground states were found for both Fe- N-2(+) and Fe-N-2(-). The adiabatic ionization potential, electron aff inity, and electronegativity were also computed; the predicted values are 7.2, 1.22, and 4.2 eV, respectively. (C) 1997 John Wiley & Sons, I nc.