title: Cyano-bridged pentanuclear and honeycomblike M(III)Cu(II) (M = Fe, Cr) bimetallic assemblies: structural variations modulated by side groups of macrocyclic ligands and magnetic properties.
abstract: Three two-dimensional (2D) layered M(III)-Cu(II) (M = Fe, Cr) bimetallic complexes and a discrete cluster were prepared using [M(CN)(6)](3-) and respective Cu macrocycles with methyl (1, 3) or ethyl (2, 4) side groups. The crystal structures can be described as aesthetic honeycomb-like M(2)Cu(3) neutral sheets (1, 3, 4) and a pentanuclear Fe(2)Cu(3) entity (2) with an isolated Cu(L2)(2+) moiety. The steric hindrance induced by the pendant groups renders the internal parameters of the Cu-N(ax) (where the "ax" subscript denotes axial) length and Cu-N(ax)-C(ax) angle to become elongated and acute. The magnetic data disclose that ferromagnetic couplings are transmitted between M(III) and Cu(II) ions through the CN links. For 4, particularly, there is a magnetically defined chain (J(c)) composed of dimers (J(d)) and trimers (J(t)), based on the structural considerations. The intramolecular magnetic coupling constants are J(d) = 3.73 cm(-1) and J(t) = 4.08 cm(-1), while the J(c) value corresponds to 0.17 cm(-1). From a magnetostructural point of view, it is reasoned that the Cu-N(ax) bond length is probably a determining factor of the strength of magnetic couplings in 4.
authors.affiliation: Department of Chemistry, Korea University, Seoul 136-701, Korea.
authors.forename: Jeong Hak
authors.initials: JH
authors.lastname: Lim
authors.forename: Jung Hee
authors.initials: JH
authors.lastname: Yoon
authors.forename: Sang Yup
authors.initials: SY
authors.lastname: Choi
authors.forename: Dae Won
authors.initials: DW
authors.lastname: Ryu
authors.forename: Eui Kwan
authors.initials: EK
authors.lastname: Koh
authors.forename: Chang Seop
authors.initials: CS
authors.lastname: Hong