ABSTRACT
Reaction of Ni(OTf)2 with the bisbidentate quaterpyridine ligand L results in the self-assembly of a tetrahedral, paramagnetic cage [NiII 4 L 6]8+. By selectively exchanging the bound triflate from [OTfâNiII 4 L 6](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 [MIIX4âNiII 4 L 6](OTf)6, where MIIX4 2- = MnCl4 2- (2), CoCl4 2- (5), CoBr4 2- (6), NiCl4 2- (7), and CuBr4 2- (8) or [MIIIX4âNiII 4 L 6](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 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 Δ or Λ stereochemistry. Magnetic susceptibility and magnetisation data show that the magnetic exchange between metal ions in the host [NiII 4] complex, and between the host and the MX4 n- 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 MX4 n- guest molecules lead to stronger host-guest magnetic exchange interactions.
