title: Crystal Structures and Magnetic Properties of Novel [Ln(III)Cu(II)(4)] (Ln = Gd, Dy, Ho) Pentanuclear Complexes. Topology and Ferromagnetic Interaction in the Ln(III)-Cu(II) Pair.
abstract: The first pentanuclear complexes of formula {Dy[Cu(apox)](2)[Cu(apox)(H(2)O)](2)}[ClO(4)](3).7H(2)O (1), {Ho[Cu(apox)][Cu(apox)(H(2)O)](3)}[PF(6)](3).4.5H(2)O (2), {Gd[Cu(apox)](2)[Cu(apox)(H(2)O)](2)}[ClO(4)](3).7H(2)O (3) and {Gd[Cu(apox)][Cu(apox) (H(2)O)](3)}[PF(6)](3).4.5H(2)O (4) (H(2)apox = N,N'-bis(3-aminopropyl)oxamide) have been synthesized. The crystal structures of complexes 1 and 2 have been determined by X-ray diffraction methods. Complexes 3 and 4 are isostructural with 1 and 2, respectively. Crystallographic data are as follows: 1 and 3, monoclinic, space group C2/c and Z = 4, with a = 14.646(6) Å, b = 29.496(7) Å, c = 16.002(7) Å, and beta = 111.76(2) degrees for 1 and a = 14.523(6) Å, b = 29.441(6) Å, c = 15.925(8) Å, and beta = 111.90(4) degrees for 3; 2 and 4, triclinic, P&onemacr;, and Z = 2, with a = 14.346(2) Å, b = 14.454(2) Å, c = 18.107(4) Å, alpha = 90.95(2) degrees, beta = 110.75(2) degrees, and gamma = 106.77(2) degrees for 2 and a = 14.365(6) Å, b = 14.496(5) Å, c = 18.172(7) Å, alpha = 91.27(3) degrees, beta = 110.74(3) degrees, and gamma = 106.67(3) degrees for 4. A tripositive ion is present in these structures, the electroneutrality being achieved by three uncoordinated perchlorate (1) or hexafluorophosphate (2) anions. The lanthanide cations are eight-coordinate with a pseudo-square-antiprismatic environment formed by carbonyl oxygen atoms from two [Cu(apox)] and two Cu(apox)(H(2)O)] (1) and one [Cu(apox)] and three [Cu(apox)(H(2)O)] (2) bidentate ligands. The temperature dependence of the magnetic susceptibility of complexes 1-4 was investigated in the range 1.8-300 K. The ligand-field effect, as well as the mixing of the free-ion states in Dy(III) and Ho(III), make extremely difficult the analysis of the overall antiferromagnetic interaction which is observed for complexes 1 and 2. The magnetic susceptibility data for complexes 3 and 4 have shown that the ground-state spin for the [Gd(III)Cu(II)(4)] unit is S = 11/2, the Gd(III)-Cu(II) interaction being ferromagnetic with an interaction parameter J(GdCu) = 0.85 cm(-)(1) (the interaction Hamiltonian is of the form H = -JS(A).S(B)). The field dependence of the magnetization at 2 K of 3 and 4 confirms the nature of the ground state and of the Gd(III)-Cu(II) interaction. The influence of the topology and of the type of bridging ligand on the nature and magnitude of the magnetic interaction in the Gd(III)-Cu(II) pair is analyzed and discussed in light of available magnetostructural data.
authors.affiliation: Departament de Química Inorgànica, Facultat de Química de la Universitat de València, Dr. Moliner 50, 46100 Burjassot (València), Spain, Laboratoire des Matériaux, URA CNRS No. 445, INP Ecole Nationale Supérieure de Chimie de Toulouse, 118 Route de Narbonne, 31077 Toulouse, France, and Laboratoire de Chimie Inorganique, URA CNRS No. 420, Université de Paris-Sud, 91420 Orsay, France.
authors.forename: José Luis
authors.initials: JL
authors.lastname: Sanz
authors.forename: Rafael
authors.initials: R
authors.lastname: Ruiz
authors.forename: Alain
authors.initials: A
authors.lastname: Gleizes
authors.forename: Francesc
authors.initials: F
authors.lastname: Lloret
authors.forename: Juan
authors.initials: J
authors.lastname: Faus
authors.forename: Miguel
authors.initials: M
authors.lastname: Julve
authors.forename: Juan José
authors.initials: JJ
authors.lastname: Borrás-Almenar
authors.forename: Yves
authors.initials: Y
authors.lastname: Journaux