Exploiting host-guest chemistry to manipulate magnetic interactions in metallosupramolecular M4L6 tetrahedral cages

Reaction of Ni(OTf)(2) with the bisbidentate quaterpyridine ligand L results in the self-assembly of a tetrahedral, paramagnetic cage [(Ni4L6)-L-II](8+). By selectively exchanging the bound triflate from [OTf subset of (Ni4L6)-L-II](OTf)(7) (1), we have been able to prepare a series of host-guest complexes that feature an encapsulated paramagnetic tetrahalometallate ion inside this paramagnetic host giving [(MX4)-X-II subset of (Ni4L6)-L-II](OTf)(6), where (MX42-)-X-II = MnCl42- (2), CoCl42- (5), CoBr42- (6), NiCl42- (7), and CuBr42- (8) or [(MX4)-X-III subset of (Ni4L6)-L-II](OTf)(7), where (MX4-)-X-III = FeCl4- (3) and FeBr4- (4). Triflate-to-tetrahalometallate exchange occurs in solution and can also be accomplished through single-crystal-to-single-crystal transformations. Host-guest complexes 1-8 all crystallise as homochiral racemates in monoclinic space groups, wherein the four {NiN6} vertexes within a single Ni4L6 unit possess the same Delta or Lambda stereochemistry. Magnetic susceptibility and magnetisation data show that the magnetic exchange between metal ions in the host [Ni-4(II)] complex, and between the host and the MX4n- guest, are of comparable magnitude and antiferromagnetic in nature. Theoretically derived values for the magnetic exchange are in close agreement with experiment, revealing that large spin densities on the electronegative X-atoms of particular MX4n- guest molecules lead to stronger host-guest magnetic exchange interactions.

Automated summary

The reaction of Ni(OTf)(2) with the bisbidentate quaterpyridine ligand L leads to the self-assembly of a tetrahedral, paramagnetic cage [(Ni4L6)-L-II](8+). By selectively exchanging the triflate, a series of host-guest complexes with encapsulated paramagnetic tetrahalometallate ions have been prepared. Magnetic susceptibility and magnetisation data suggest comparable and antiferromagnetic magnetic exchange interactions between metal ions in the host complex and the guest species.