CloseEncounters of the Weak Kind: Investigationsof Electron–Electron Interactions between Dissimilar Spinsin Hybrid Rotaxanes

摘要

We report a family of hybrid [2]rotaxanes based on inorganic [Cr7NiF8(O2C^tBu)16]⁻ (“{Cr7Ni}”) rings templated about organic threads that are terminated at one end with pyridyl groups. These rotaxanes can be coordinated to [Cu(hfac)2] (where Hhfac = 1,1,1,5,5,5-hexafluoroacetylacetone), to give 1:1 or 1:2 Cu:{Cr7Ni} adducts: {[Cu(hfac)2](py-CH2NH2CH2CH2Ph)[Cr7NiF8(O2C^tBu)16]}, {[Cu(hfac)₂][py-CH₂NH₂CH₂CH₃][Cr₇NiF₈(O₂C^tBu)₁₆]}, {[Cu(hfac)₂]([py-CH₂CH₂NH₂CH₂C₆H₄SCH₃][Cr₇NiF₈(O₂C^tBu)₁₆])₂}, {[Cu(hfac)₂]([py-C₆H₄-CH₂NH₂(CH₂)₄Ph][Cr₇NiF₈(O₂C^tBu)₁₆])₂}, and {[Cu(hfac)₂]([3-py-CH₂CH₂NH₂(CH₂)₃SCH₃][Cr₇NiF₈(O₂C^tBu)₁₆])₂}, the structures of which have been determined by X-ray diffraction. The {Cr₇Ni} rings and Cu^II ions both have electronic spin S = 1/2, but with very different >g-values. Continuous-wave EPR spectroscopy reveals the exchange interactions between these dissimilar spins, and hence the communication between the different molecular components that comprise these supramolecular systems. The interactions are weak such that we observe AX or AX₂ type spectra. The connectivity between the {Cr₇Ni} ring and thread terminus is varied such that the magnitude of the exchange interaction J can be tuned. The coupling is shown to be dominated by through-bond rather than through-space mechanisms.