Spectator ligand effects on the vibrational spectra of heteroleptic complexes of ruthenium with bipyrazine

Resonance Raman (RR) and transient resonance Raman (TR2) spectra were acquired for a series of heteroleptic complexes of ruthenium, i.e. RuL2(bpz)2+, where bpz is 2,2′‐bipyrazine and L is 2,2′‐bipyridine (bpy) or an alkylated 2,2′‐bipyridine [i.e. diazafluorene (daf) or 4,4′‐dimethyl‐5,5′‐diethyl‐2,2′‐bipyridine (dmdeb)]. Resonance Raman spectra acquired at different excitation wavelengths for the ground‐state complexes reveal selective enhancement of modes associated with the coordinated bpz or the spectator ligands, as expected. The TR2 spectra, acquired with excitation at 355 nm, confirm selective population of a bpz‐localized 3MLCT excited state for each complex. Both the ground‐state RR spectra and the excited state TR2 data indicate that only slight shifts are observed in a few modes as the donor strengths of the spectator ligands are varied. Such data for a systematically manipulated set of complexes, acquired here for the first time, imply that both the RR and TR2 spectral parameters are reliably characteristic for a given ligand, varying only slightly as the nature of other ligands in the complex is changed.