Preparation, crystal structures and magnetic properties of 12-metallacrown-4 complexes with the donors on the organic periphery of molecule

As the precursors of molecular magnets, three metallacrown analogous complexes, [Cu(II)(12-MC(Cu(II)N(ahpha))-4)]·(NO₃)₂·4H₂O (1), [Cu(II)(12-((II)N(hbha))-4)]·(NO₃)₂·8H₂O (2) and [Cu(II)(12-MC(Cu(II)N(mha))-4)]·(OH)₂·12H₂O (3) (H₂ahpha = 3-amino-3-hydroximino propanoic hydroximic acid, H₂hbha = 3-hydroximino butanoic hydroximic acid and H₂mha = malonic hydroximic acid) have been prepared and 1 and 2 are characterized structurally. The number of donors on the organic periphery of the molecular sheet is modified with additional hydroxy and R group of ligands for modulating the intermolecular architecture of metallacrown molecules and enhancing intermolecular magnetic interaction. Solid-state magnetic susceptibility studies 5-300 K of 1 and 2 show a strongly antiferromagnetic intramolecular exchange between the five Cu(II) centers and weakly antiferromagnetic intermolecular interaction. The fitting of H = - 2J₁ Σ(i=1)/4 S(i)·S₅ - 2J₂ Σ(i≠j=1)/4 S(i)·S(j) to the experimental magnetic susceptibilities give g = 2.066(3), J₁ = - 119.9(7), J₂ = -79.0(4), zJ' = - 0.69(7) cm^-1 for 1 and g = 2.089(3), J₁ = - 163(2), J₂ = - 85.1(6), zJ' = - 0.61(7) cm^-1 for 2. (C) 2000 Elsevier Science S.A.