Resonance enhancement of the Raman-spectrum of bipyridyl gold(iii) chloro complexes

Using exciting wavelengths in the visible region, both bipyridyl Au2Cl6 and bipyridyl AuCl3 are shown to exhibit resonance-enhanced Raman scattering. The enhancement in bipyridyl Au2Cl6 is largest with 488.0 and 514.5 nm excitation, both bipyridyl ring and metal-ligand stretching vibrations are affected to about the same extent. The electronic transitions which give rise to the enhancement are assigned as transitions involving σ molecular orbitals delocalized over the complete molecule. In the resonance profile of bipyridyl AuCl3, there were three peaks at 568.2, 514.4 and below 476 nm and, in addition, there is a probable B term enhancement. In this molecule the resonance arises from transition between more localized molecular orbitals assigned as due to a transition on the gold-nitrogen bond, to π→π* transitions on the bipyridyl ring and the B term to a transition located mainly on the gold-chloride bonds. Some of these enhancements can be correlated with weak structure observed in the 10 K absorption spectrum of the complex.