Molecular architectures for trimetallic d/f/d complexes: Magnetic studies of a LnCu(2) core

Five new trinuclear Cu-Ln-Cu cluster complexes have been prepared by a one-pot reaction using H(3)bcn (tris-N,N’,N"-(2-hydroxybenzyl)-1,4,7-triazacydononane) and Ln = La(III), Nd(III), Gd(III), Dy(III), and Yb(III) where the d- and f-block metal ions are in close proximity desirable for magnetic studies. The [LnCu(2)(bcn)(2)]ClO4 center dot nH(2)O complexes possess the same stoichiometry as the previously reported [LnNi(2)(bcn)(2)]ClO4 center dot nH(2)O and [LnZn(2)(bcn)(2)]ClO4 center dot nH(2)O systems. Additionally, the solid state structures of the LnCu(2) complexes appear to be isostructural to the LnNi(2) and LnZn(2) species as determined by their nearly superimposable IR spectra. The similarities in the structures of the [LnTM(2)(bcn)(2)]ClO4 center dot nH(2)O series, where TM = Zn(II), Ni(II),.and Cu(II), allow for direct comparison of their magnetic exchange. An empirical approach, removing first-order anisotropic contributions determined from the analogous [LnZn(2)(bcn)(2)]ClO4 center dot nH(2)O was used to study the d/f/d spin interactions in the [LnCu(2)(bcn)(2)]ClO4 center dot nH(2)O complexes. A ferromagnetic exchange was determined where Ln = Gd(III), Dy(III), or Yb(III) and an antiferromagnetic exchange for Ln = Nd(III), identical to the magnetic exchange observed for the [LnNi(2)(bcn)(2)]ClO4 center dot nH(2)O complexes. An exchange integral of 3.67 cm(-1) for the trimetallic [GdCu2(bcn)(2)]ClO4 center dot 3H(2)O species was determined using a modified spin Hamiltonian. The [Cu(Hbcn)] and the [Cu-3(Hbcn)(2)](ClO4)(2) building blocks of the larger coaggregated d/f/d species were also synthesized, and their structures are reported.