Thermodynamic and spectroscopic parameters in metal complexes: extension of a linear relationship to nickel(II) derivatives

A previous correlation between the electronic spectra of some 30 copper(II) complexes and their electronic band max. was extended to nickel(II) and iron(II). Three alternative correlations are reported from some 40 nickel(II) complexes contg. 1 to 6 amine ligands. These involve correlations with directly observable transition energies and also with a calcd. function based on the orbital angular overlap model. The difference (σN - σO) correlates well with -ΔHf in substituted complexes. Although only very limited data are available, iron(II) amine derivs. exhibit similar behavior. Outer-sphere solvation energies cancel, fortuitously, from this correlation. These studies now permit the derivation of heats of formation of amine complexes of copper(II), nickel(II), and possibly iron(II) with reasonable accuracy.