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

Abstract

The acetylacetonate complexes [Ni₂L¹(acac)(MeOH)]·H₂O, 1·H₂O and [Ni₂L³(acac)(MeOH)]·1.5H₂O, 2·1.5H₂O (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 [Ni₂HL^x(o-O₂CC₆H₄CO₂)(H₂O)]·nMeOH and [Ni₂HL^x(O₂CCH₂CO₂)(H₂O)]·nH₂O dicarboxylate complexes (x = 1, 3; n = 1–3). The crystal structures of [Ni₂HL¹(o-O₂CC₆H₄CO₂)(H₂O)]·MeOH, 3·MeOH, [Ni₂HL³(o-O₂CC₆H₄CO₂)(H₂O)]·3MeOH, 4·3MeOH and [Ni₂HL¹(O₂CCH₂CO₂)(H₂O)]·2.5H₂O·0.25MeOH·MeCN, 5·2.5H₂O·0.25MeOH·MeCN, were solved. Complexes 3–5 show dinuclear [Ni₂HL^x(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.