Conducting the same experiment in d 3 -MeCN-D2O (9 : 1) and observing the reaction mixture directly by 1 H NMR without first quenching aliquots (Figure ) revealed that [Cu a Cu b (5)]PF6 is converted to a new species at short reaction times under these conditions (Figure vs Figure ). However, once again, aqueous work up of aliquots, even after 24 h (Figure (Figure ). This suggests that the initial increase in absorbance by UV-vis is due to formation of this cyanide adduct. Furthermore, allowing the reaction mixture to stand for longer times fortuitously allowed us to identify a second crystalline product, SCXRD analysis of which revealed it to be [Cu b (CN)(5)H]. Portion-wise addition of [Cu(MeCN)4]PF6 to 5H, monitored by 1 H NMR, revealed the quantitative formation first of [Cu a (5H)] + followed by a new species. Slow evaporation of Et2O into a MeCN solution of the same species obtained using excess CuClO4 produced crystals suitable for SCXRD which suggests that this new species is [Cu a Cu c (5H)] 2+ in which the second metal ion is bound in a three-coordinate environment provided by N 2 of the triazole and the bipyridine N donors of the second macrocycle. Unsurprisingly, the second Cu I center of [Cu a Cu c (5H)] 2+ was readily removed to give [Cu a (5H)] + by washing of a solution of the complex with ammoniacal EDTA. We note that even extended stirring under these conditions did not remove Cu a , whereas the Cu I ion in Sauvage's original catenane complex is readily removed under these conditions. These results suggest that, perhaps unsurprisingly, the 4N chelate provided by 5H is highly preorganized to bind Cu I . For comparison we examined the coordination of Ag I , which is also a monovalent d 10 ion but has a larger ionic radius than Cu I (0.99 vs 0.75 Å) . Portion-wise addition of AgSbF6 monitored by H NMR first produced a new species that we tentatively assign as [Ag a (5H)] + based on the similarity of the corresponding 1 H NMR spectrum to that of [Cu a (5H)] + of further portions of AgSbF6 produced [Ag a Ag c (5H)] 2+ , the structure of which was confirmed by SCXRD. Washing a solution of [Ag a Ag c (5H)] 2+ with ammoniacal EDTA led to recovery of the species assigned as [Ag a (5H)] + , confirming that, as with Cu I , the second Ag I is bound less strongly. Addition of Ag I (10 equiv.) to a solution of [Cu a (5H)] + gave a new complex that was identified by SCXRD as [Cu a Ag c (5H)] 2+ , demonstrating that Ag I is not able to displace Cu I from the 4N binding pocket. Conversely, addition of Cu I (10 equiv.) to a solution of [Ag a Ag c (5H)] 2+ resulted in the slow formation of [Cu a Cu c (5H)] 2+ over 48 h, confirming that Cu I can displace Ag I , presumably due to the difference in their ionic radii which suggests that the 4N binding pocket is better suited to Cu I .