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.

Mechanically chelating ligands have untapped potential for the engineering of metal ion properties by providing reliable control of the number, nature and geometry of donor atoms, akin to how a protein cavity

In this paper, the optimization of the synthesis of 3,7‐bis(N‐methyl‐N‐phenylamino)phenothiazinium chloride with a detailed analysis of reaction parameters, i.e. solvent, temperature, amount of amine, as well as addition of a non‐nucleophilic base, is presented. Spectroscopic, electrochemical and computational data show that the presence of the two phenyl rings, directly bound on the PTZ+ core, inhibits the aggregation ability of the salt at concentrations up to 10–3 M. Furthermore, the introduction of an aromatic group in phenothiazinium‐based molecules appears strategic to introduce other useful functionalities, thus opening new opportunities in the drug design/discovery research field.

Mechanically chelating ligands have untapped potential for the engineering of metal ion properties by providing reliable control of the number, nature and geometry of donor atoms, akin to how a protein cavity controls the properties of bound metal ions. Here we demonstrate this principle in the context of Co^II-based single-ion magnets. Using multi-frequency EPR, susceptibility and magnetization measurements we found that these complexes show some of the highest zero field splittings reported for five-coordinate Co^II complexes to date. The predictable coordination behavior of the interlocked ligands allowed the magnetic properties of their Co^II complexes to be evaluated computationally <i>a priori </i>and our combined experimental and theoretical approach enabled us to rationalize the observed trends. The predictable magnetic behavior of the rotaxane Co^II complexes demonstrates that interlocked ligands offer a new strategy to design metal complexes with interesting functionality.