Is ferromagnetism an intrinsic property of the CuII/GdIII couple? 2. Structures and magnetic properties of novel trinuclear complexes with mu-phenolato-mu-oximato (Cu-Ln-Cu) cores (Ln = La, Ce, Gd).
The present paper is devoted to the study of original trinuclear (CuII, LnIII, CuII) complexes (Ln = La, Ce, Gd). They derive from the polydentate ligands H2Li (i = 1, 3, 4) represented in Figure 1. The crystal and molecular structures of two complexes have been determined at room temperature. The (Cu, Gd, Cu) complex of H2L1 1Gd and the (Cu, Ce, Cu) complex of H2L3 3Ce crystallize in the triclinic space group P1 (no. 2) with the following cell parameters: a = 14.005(2) A, b = 14.7581(13) A, c = 11.3549(13) A, alpha = 96.273(9) degrees, beta = 97.648(11) degrees, gamma = 72.946(9) degrees, V = 2217.7(4) A3, and Z = 2 for 1Gd and a = 11.226(2) A, b = 16.927(3) A, c = 11.010(2) A, alpha = 108.67(2) degrees, beta = 110.48(1) degrees, gamma = 92.35(2) degrees, V = 1828.7(5) A3, and Z = 2 for 3Ce. Regarding possible supports for magnetic interactions, it may be noted that, in both complexes, each of the main bridging pathways between the equatorial positions of a copper(II) ion and the related lanthanide ion is double and not symmetrical. It involves a phenolato oxygen atom and an oximato nitrogen-oxygen pair of atoms. The resulting Cu(O,N-O)Gd networks are not planar, but 3Ce displays much larger deviations than does 1Gd. Determination of the thermal dependence of chi M (molar susceptibility) and the field variations of M (magnetization) show that in 3Gd and 4Gd the Cu-Gd interactions are antiferromagnetic while more "usual" ferromagnetic interactions are observed for 1Gd. The possibility of a relationship between structural and magnetic parameters is considered.
Costes
J P
JP
Laboratoire de Chimie de Coordination du CNRS, UPR 8241, liée par conventions à l'Université Paul Sabatier et à l'Institut National Polytechnique de Toulouse, 205 route de Narbonne, 31077 Toulouse, France. costes@lcc-toulouse.fr
Dahan
F
F
Dupuis
A
A