Transient resonance Raman spectroscopy and DFT calculations of metal‐to‐ligand charge transfer states of Cu(I) complexes of substituted 1,10‐phenanthroline ligands and their perdeuterated isotopomers

Abstract

AbstractCu(I) complexes of the type [Cu(L)(PPh3)2]+, where L is the bidentate ligand 4,7‐diphenyl‐1, 10‐phenanthroline (dip) and 3,4,7,8‐tetramethyl‐1,10‐phenanthroline (tem) and their perdeuterated analogues, have been synthesised and the transient resonance Raman spectra of these complexes have been measured. The spectra show two sets of bands, one due to the PPh3 ligands and the other due to L.− created through the metal‐to‐ligand charge transfer transition. Density functional theory calculations have been used to model ligands and complexes in the ground state and good agreement has been found between calculated and measured bands with a mean absolute deviation of 8–10 cm−1 for the ligands and 5 cm−1 for the complexes. Shifts in the bands due to deuteration have also been well predicted, with the shifts for most modes predicted to within 10 cm−1. The structure and spectra of the excited states have been modelled using two approaches. The reduced state [Cu(L.−)(PH3)2] was used for both complexes to predict the changes in the structure of the polypyridyl ligand and for [Cu(dip)(PPh3)2]+ the triplet state was also optimised. Both approaches show that similar structural changes in the ligand are predicted. In the case of [Cu(dip)(PPh3)2]+* and [Cu(dip.−)(PPh3)2], the calculated states are 3A2 and 2A2, respectively, consistent with experiment. Calculations on [Cu(tem)(PPh3)2]+* give a 3B1 state. This is not consistent with experimental results. For [Cu(tem.−)(PPh3)2] both the 2B1 and 2A2 states may be calculated and the experimental spectrum of [Cu(tem)(PPh3)2]+* is closer to that of the 2A2 [Cu(tem.−)(PPh3)2] species. Calculated wavenumbers are compared to measured transient resonance Raman L.− bands and found to have a mean absolute deviation of 8 cm−1 for the triplet state of [Cu(dip)(PPh3)2]+ and 16 cm−1 for the reduced state of [Cu(tem)(PPh3)2]+. Copyright © 2008 John Wiley & Sons, Ltd.