Ni(N2)4 revisited: an analysis of the Ni–N2 bonding properties of this benchmark system on the basis of UV/Vis, IR and Raman spectroscopy

Abstract

Matrix isolation of Ni atoms in an N₂ matrix leads to the formation of Ni(N₂)₄. This compound, being isoelectronic with the well known Ni(CO)₄, represents an important bench-mark system. It has been characterised experimentally by UV/Vis, IR and Raman spectra. The vibrational spectra give evidence for both a₁ modes, three of the four t₂ modes, and one of the two e modes of the T_d symmetric molecule. The experimental data obtained for Ni(¹⁴N₂)₄ and Ni(¹⁵N₂)₄ were used to determine the valence force constants f(Ni–N) and f(N–N), which are compared with those derived for Ni(N₂) and for the corresponding carbonyl complexes Ni(CO) and Ni(CO)₄. In addition, several overtones and combination modes of Ni(N₂)₄ were observed for the first time, providing further valuable information about the bond properties. The data allow for the first time a direct estimate of the Ni–N₂ bond energy in Ni(N₂)₄ (120 kJ mol⁻¹), that compares with a value of 148 kJ mol⁻¹ determined by the same method for Ni(CO)₄.