A General Route to Strictly Dinuclear Cu(II)/Ln(III) Complexes. Structural Determination and Magnetic Behavior of Two Cu(II)/Gd(III) Complexes

Starting from a single precursor, bis(3-methoxysalicylaldehydato)copper (II), which contains an O(4)Cu chromophore, three routes to discrete dinuclear Cu(II)/Ln(III) complexes (Ln = Pr, Eu, Gd, Yb) are described. The pairs of chromophores occurring in the resulting complexes are either O(4)Cu/O(4)Ln or O(2)N(2)Cu/O(4)Ln, the coordination sphere of the Ln ions being completed, in both cases, with six oxygen atoms afforded by three nitrato ions. Two Cu/Gd complexes involving either two tridentate ligands (2) or one hexadentate ligand (7) have been structurally characterized. They crystallize in the monoclinic space groups P2(1)/n (No. 14) (2) and P2(1)/c (No. 14) (7). The cell parameters are a = 9.7185(7) Å, b = 16.7839(12) Å, c = 14.8868(8) Å, beta = 97.445(5) degrees, and Z = 4 (2) and a = 9.7656(9) Å, b = 19.889(2) Å, c = 15.870(2) Å, beta = 95.512(9) degrees, and Z = 4 (7) respectively. The magnetic properties of six Cu/Ln complexes have been determined. A quantitative analysis of the magnetic properties of the Cu/Gd complexes shows that the interaction is of the ferromagnetic type with a J constant varying from 4.8 to 7.0 cm(-)(1). The decrease of the interaction parallels the variation of the dihedral angle between the two halves (OCuO and OGdO) of the bridging core.