Sauvage and co-workers quantified the enhanced stability of their catenane-based Cu I complex by monitoring its reaction with different concentrations of KCN in MeCN-H2O using UV-vis spectroscopy . To quantitatively compare the stability of [Cu a Cu b (5)]PF6 with this previous report we attempted a similar study with under the same conditions. However, unexpectedly, after addition of KCN the absorption of the solution increased to a maximum over 50 minutes before then decreasing slowly (Figure ). The first process appears too fast to be consistent with the slow reaction of [Cu a Cu b (5)]PF6 observed during the 1 H NMR study of the same reaction (vide supra), albeit this was conducted in MeCN-H2O, whereas the second slower process is more consistent with the reaction rates observed by 1 H NMR. Repeating the experiment with different equivalents of KCN revealed similar behavior albeit a larger initial increase in absorption was observed with increasing equivalents of KCN, alongside a faster subsequent decrease in absorption (Figure ).