Evaluation of the donor ability of phenanthrolines in iridium complexes by means of synchrotron radiation photoemission spectroscopy and DFT calculations

Synchrotron radiation XPS measurements of Ir 4f, N 1s and I 4d core levels for the compounds Ir(cod)(N-N)X (cod = 1,5-cyclooctadiene; N-N = 1,10-phenanthroline and substituted derivatives; X = Cl, I) are reported. The compounds Ir(cod)(3,4,7,8-Me(4)phen)X (3,4,7,8-Me(4)phen = 3,4,7,8-tetramethyl-1,10-phenanthroline) were structurally characterized by single crystal X-ray analyses. The comparison among the binding energies shows differences that are interpreted in terms of electron density variations due to the change of the phenanthroline substituents. Such analysis provides a quantitative evaluation of the ligand donor properties. The trend in the measured binding energies is confirmed by the results obtained by DFT Delta SCF calculations, which include final state relaxation effects, while the specific role of initial state effects has been assessed in terms of the Kohn-Sham eigenvalues analysis.