Encapsulation controlled single molecule magnetism in tetrathiafulvalene-capped cyanide-bridged cubes

New TTF-based (TTF = tetrathiafulvalene) ligands, L1 and L2 (L1 = alpha-(4'-methyl-4,5-ethylenedithiotetrathiafulvalene-5'-thio)-alpha'-[tris-2,2,2-(1-pyrazolyl)ethoxy]-p-xylene and L2 = alpha-(4'-methyl-4,5-dimethylthiotetrathiafulvalene-5'-thio)-alpha'-[tris-2,2,2-(1-pyrazolyl) ethoxy]-p-xylene), possessing tris-pyrazolyl coordination sites, were synthesized. The reactions of Ni(BF4)(2)center dot 6H(2)O with the TTF-ligands (L1 and L2), n-Bu4N[Fe(CN)(3)(tp or pztp)] (tp = hydrotris(pyrazol-1-yl) borate and pztp = tetrakis(pyrazol-1-yl) borate) in the presence of additional counter ions afforded two cyanide-bridged octanuclear complexes: [(Fe4Ni4II)-Ni-III(CN)(12)(pztp)(4)(L1)(4)](BF4)(4) (1) and [(Fe4Ni4II)-Ni-III(CN)(12)(pztp)(4)(L2)(4)](PF6)(4) (2). Using a similar procedure to that employed in the synthesis of complex 2, with the addition of sodium tetraphenylborate, yielded a two-electron-reduced compound, Na[(Fe2Fe2Ni4II)-Fe-III-Ni-II(CN)(12)(tp)(4)(L2)(4)](BF4)(3) (3), in which a sodium ion was encapsulated by the cube. The host-guest complex 3 showed enhanced redox behaviour and while magnetic susceptibility measurements revealed ferromagnetic interactions to be operative in all three complexes, the cation encapsulation behaviour of 3 led it to exhibit single molecule magnet-type properties.