title: Ferromagnetic coupling by spin polarization in a trinuclear copper(II) metallacyclophane with a triangular cage-like structure.
abstract: A series of trinuclear copper(II) complexes of general formula A(6)[Cu(3)L(2)] x nH(2)O [L = benzene-1,3,5-tris(oxamate); A = Li(+) (n = 8), 1a; Na(+) (n = 11.5), 1b; and K(+) (n = 8.5), 1c] have been synthesized, and they have been structurally and magnetically characterized. X-ray diffraction on single crystals of 1c shows the presence of three square-planar copper(II)-bis(oxamato) moieties which are connected by a double benzene-1,3,5-triyl skeleton to give a unique metallacyclophane-type triangular cage. The copper basal planes are virtually orthogonal to the two benzene rings, which adopt an almost perfect face-to-face alignment. Complexes 1a-c exhibit a quartet (S = 3/2) ground spin state resulting from the moderate ferromagnetic coupling (J values in the range of +7.3 to +16.5 cm(-1)) between the three Cu(II) ions across the two benzene-1,3,5-tris(amidate) bridges [H = -J(S(1) x S(2) + S(2) x S(3) + S(3) x S(1)) with S(1) = S(2) = S(3) = S(Cu) = 1/2]. Density functional theory calculations on the S = 3/2 Cu(II)(3) ground spin state of 1c support the occurrence of a spin polarization mechanism for the propagation of the exchange interaction, as evidenced by the sign alternation of the spin density in the 1,3,5-substituted benzene spacers.
authors.affiliation: Institut Parisien de Chimie Moléculaire, Université Pierre et Marie Curie-Paris 6, UMR 7201, F-75005 Paris, France.
authors.forename: Marie-Claire
authors.initials: MC
authors.lastname: Dul
authors.forename: Xavier
authors.initials: X
authors.lastname: Ottenwaelder
authors.forename: Emilio
authors.initials: E
authors.lastname: Pardo
authors.forename: Rodrigue
authors.initials: R
authors.lastname: Lescouëzec
authors.forename: Yves
authors.initials: Y
authors.lastname: Journaux
authors.forename: Lise-Marie
authors.initials: LM
authors.lastname: Chamoreau
authors.forename: Rafael
authors.initials: R
authors.lastname: Ruiz-García
authors.forename: Joan
authors.initials: J
authors.lastname: Cano
authors.forename: Miguel
authors.initials: M
authors.lastname: Julve
authors.forename: Francesc
authors.initials: F
authors.lastname: Lloret