Exploiting host-guest chemistry to manipulate magnetic interactions in metallosupramolecular M4L6tetrahedral cages

Abstract

Reaction of Ni(OTf)2with the bisbidentate quaterpyridine ligandLresults in the self-assembly of a tetrahedral, paramagnetic cage [NiII4L6]8+. By selectively exchanging the bound triflate from [OTf⊂NiII4L6](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 [MIIX4⊂NiII4L6](OTf)6, where MIIX42−= MnCl42−(2), CoCl42−(5), CoBr42−(6), NiCl42−(7), and CuBr42−(8) or [MIIIX4⊂NiII4L6](OTf)7, where MIIIX4−= 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 complexes1-8all crystallise as homochiral racemates in monoclinic space groups, wherein the four {NiN6} vertexes within a single Ni4L6unit possess the sameΔorΛstereochemistry. Magnetic susceptibility and magnetisation data show that the magnetic exchange between metal ions in the host [NiII4] 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.