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

Reaction of Ni(OTf) with the bisbidentate quaterpyridine ligand results in the self-assembly of a tetrahedral, paramagnetic cage [Ni ]. By selectively exchanging the bound triflate from [OTf⊂Ni ](OTf) (), we have been able to prepare a series of host-guest complexes that feature an encapsulated paramagnetic tetrahalometallate ion inside this paramagnetic host giving [MX⊂Ni ](OTf), where MX = MnCl (), CoCl (), CoBr (), NiCl (), and CuBr () or [MX⊂Ni ](OTf), where MX = FeCl () and FeBr (). Triflate-to-tetrahalometallate exchange occurs in solution and can also be accomplished through single-crystal-to-single-crystal transformations. Host-guest complexes all crystallise as homochiral racemates in monoclinic space groups, wherein the four {NiN} vertexes within a single NiL unit possess the same or stereochemistry. Magnetic susceptibility and magnetisation data show that the magnetic exchange between metal ions in the host [Ni ] complex, and between the host and the MX 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 MX guest molecules lead to stronger host-guest magnetic exchange interactions.