Spectroscopic and Density Functional Theory Studies of 1,10-Phenanthroline, Its Radical Anion, and [Cu(Phen)(PPh₃)₂]⁺

Abstract

The vibrational spectra (Raman and IR) of 1,10-phenanthroline (phen), its perdeuterated analogue (d8-1,10-phenanthroline, d8-phen), and the copper(I) complexes [Cu(phen)(PPh3)2]+ and [Cu(d8-phen)(PPh3)2]+ have been measured. These spectra may be modeled using DFT calculations (B3LYP/6-31G(d)). The calculated structure compares favorably with crystallographic data. The time-resolved resonance Raman spectra of the copper(I) complexes were used to provide spectral signatures of phen• - and d8-phen• -. Geometries and vibrational spectra of the radical anions may be calculated in two ways: first as phen• -, which has been previously shown to be a 2B1 state. Calculations with B3LYP require the 6-311+G(d,p) basis set in order to predict this state correctly for the radical anion, rather than the close-lying 2A2 state, therefore giving a reasonable prediction of the geometry and spectra. Second, using [Cu(phen• -)(PH3)2] it is possible to model the radical anion at the B3LYP/6-31G(d) level because the metal center stabilizes the b1 singly occupied ligand MO. The calculated spectra of [Cu(phen• -)(PH3)2] and its perdeuterated analogue compare favorably with experimental data for the excited state of the complexes.