An unexpected twisted structure for the 2,2′-bipyridine anion radical evidenced by resonance Raman spectra simulations

The geometry of the anion radical of 2,2′-bipyridine has been optimized at the ROHF/6-31G* level of theory in three point groups: C2h (trans-planar geometry), C2v (cis-planar geometry), and C2 (twisted transoid geometry). Comparison of experimental and calculated frequencies shows a best agreement for the twisted structure. Further investigation of the geometry of this species has been realized by the simulation of the relative Raman intensities in resonance with two different electronic transitions. Comparison of these data with the corresponding experimental resonance Raman spectra brings additional evidence that the 2,2′-bipyridine anion radical does not adopt a planar configuration.