Early work by Sauvage revealed that mechanical bonding alters the stability and redox properties of their original catenane metal complexes. However, despite the importance of controlling metal ion properties for a range of applications, these effects have received relatively little attention since. Here we present a series of tri-, tetra-and pentadentate rotaxane-based ligands, a detailed study of their metal binding behavior and, where possible, compare their redox and electronic properties with their non-interlocked counterparts. The rotaxane ligands form complexes with most of the metal ions investigated and x-ray diffraction revealed that in some cases the mechanical bond enforces unusual coordination numbers and distorted arrangements as a result of the exclusion of exogenous ligands driven by the sterically crowded binding sites. In contrast, only the non-interlocked equivalent of the pentadentate rotaxane Cu II complex could be formed selectively, and this exhibited compromised redox stability compared to its interlocked counterpart. Frozen-solution EPR data demonstrate the formation of an interesting biomimetic state for the tetradentate Cu II rotaxane, as well as the formation of stable Ni I species and the unusual coexistence of high-and low-spin Co II in the pentadentate framework. Our results demonstrate that readily available mechanically chelating rotaxanes give rise to complexes the non-interlocked equivalent of which are inaccessible, and that the mechanical bond augments the redox behavior of the bound metal ion in a manner analogous to the carefully-tuned amino acid framework in metalloproteins.

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Synthesis, crystal structure investigation, DFT analyses and antimicrobial studies of silver(I) complexes with N,N,N 0 ,N 00 -tetrakis(2-hydroxyethyl/propyl) ethylenediamine and tris(2-hydroxyethyl)amine †

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