Heavy-atom tunnelling in Cu(ii)N 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 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)]SO more than 40 years ago, without the authors realizing that it was a quantum outcome.