Hexa-, hepta- and dodeca-nuclear nickel(II) complexes of three Schiff-base ligands derived from 1,4-diformyl-2,3-dihydroxybenzene

Three new closely-related diimine ligands, H4L1, H4L2 and H4L3, were prepared by the condensation of 1,4-diformyl-2,3-dihydroxybenzene (1) with two equivalents of 2-aminoethanol, 3-aminopropanol or 2-aminophenol, respectively. Three polynuclear complexes, [Ni-7(II)(H2L1)(4)(OAc)(6)(H2O)(2)]center dot 5H(2)O (2 center dot 5H(2)O), [Ni-6(II)(H2L2)(2)(OAc)(6)(mu-OMe)(2)(H2O)(2)]center dot 5H(2)O (3 center dot 5H(2)O) and [Ni-12(II)(L-3)(6)(MeOH)(7)(H2O)(3)]center dot 4H(2)O (4 center dot 4H(2)O), were prepared by reaction of the appropriate ligand with 1.50/1.75, 1.75/3.00 or 2.00 equivalents, respectively, of nickel(II) acetate tetrahydrate, in methanol. The crystal structures of these complexes are very different to one another, despite what initially appear to be relatively minor ligand modifications. While [Ni-7(II)(H2L1)(4)(OAc)(6)(MeOH)(2)]center dot 7MeOH center dot 4H(2)O possesses C-2 symmetry and has a 4:7 L:M ratio, [Ni-6(II)(H2L2)(2)(OAc)(6)(mu-OMe)(2)(MeOH)(2)]center dot 0.5MeOH center dot 0.5H(2)O center dot Et2O and [Ni-12(II)(L-3)(6)(MeOH)(6.5)(H2O)(3.5)]center dot solvent have no internal symmetry and have L:M ratios of 2:6 and 6:12, respectively. Two of the four ligands in [Ni-7(II)(H2L2)(4)(OAc)(6)(MeOH)(2)] are in similar planes, whilst the two remaining ligands are near perpendicular to these planes. The six ligands in [Ni-12(II)(L-3)(6)(MeOH)(6.5)(H2O)(3.5)] adopt an offset grid-like arrangement with eight of the twelve metal ions at the intersections of the perpendicular, offset, ligands. In contrast, [Ni-6(II)(H2L2)(2)(OAc)(6)(mu-OMc)(2)(MeOH)(2)] features an [Ni-4(II)(OR)(4)] cubane core with wing tips of the remaining two nickel(II) ions. All three complexes were subsequently prepared in stoichiometric syntheses, in yields of 50% (2 center dot 5H(2)O), 48% (3 center dot 5H(2)O) and 62% (4 center dot 4H(2)O). The magnetic properties of 2 center dot 5H(2)O, 3 center dot 5H(2)O, 4 center dot 4H(2)O are consistent with intra-complex antiferromagnetic coupling dominating overall, and therefore all three complexes display low spin ground states.