Dinuclear nickel complexes with a Ni2O2 core:: a structural and magnetic study

The acetylacetonate complexes [Ni2L1(acac)(MeOH)]center dot H2O, 1 center dot H2O and [Ni2L3(acac)(MeOH)]center dot 1.5H(2)O, 2.1.5H(2)O (H3L1 = (2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine and H3L3 = (2-(5-bromo-2-hydroxyphenyl)-1,3-bis[4-(5-bromo-2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) were prepared and fully characterised. Their crystal structures show that they are dinuclear complexes, extended into chains by hydrogen bond interactions. These compounds were used as starting materials for the isolation of the corresponding [Ni2HLx(o-O2CC6H4CO2)(H2O)]center dot nMeOH and [Ni2HLx(O2CCH2CO2)(H2O)]center dot nH(2)O dicarboxylate complexes (x = 1, 3; n = 1-3). The crystal structures of [Ni2HL1(o-O2CC6H4CO2)(H2O)]center dot MeOH, 3 center dot MeOH, [Ni2HL3(o- O2CC6H4CO2)(H2O)]center dot 3MeOH, 4.3MeOH and [Ni2HL1(O2CCH2CO2)(H2O)]center dot 2.5H(2)O center dot 0.25MeOH center dot MeCN, 5.2.5H(2)O center dot 0.25MeOH center dot MeCN, were solved. Complexes 3-5 show dinuclear [Ni2HLx(dicarboxylate)(H2O)] units, expanded through hydrogen bonds that involve carboxylate and water ligands, as well as solvate molecules. The variable temperature magnetic susceptibilities of all the complexes show an intramolecular ferromagnetic coupling between the Ni(II) ions, which is attempted to be rationalized by comparison with previous results and in the light of molecular orbital treatment. Magnetisation measurements are in accord with a S = 2 ground state in all cases.