Heavy-atom tunnelling in Cu(ii)N(6) complexes: theoretical predictions and experimental manifestation

The degenerate rearrangement on Jahn–Teller distorted metal complexes is a promising reaction for the observation of significant heavy atom quantum mechanical tunnelling. Herein, a family of Cu(ii)–N(6) complexes are theoretically proven to exhibit rapid dynamical Jahn–Teller tunneling even close to the absolute zero. The manifestation of our predictions apparently appeared in solid state EPR experimental measurements on [Cu(en)(3)]SO(4) more than 40 years ago, without the authors realizing that it was a quantum outcome.