Rational design of large-spin clusters based on the hexacopper(II) siloxanolate core

The hexacopper(II) siloxanolate cage [Cu-6{(PhSiO2)(6)}(2)(BuOH)(5)](.)3 (BuOH)-Bu-n has been synthesized by reaction between CuCl2 and potassium phenylsiloxanolate in n-butanol, and characterized by single-crystal X-ray diffraction, magnetic measurements and high-frequency EPR (HF-EPR). The complex exhibits a torus-like structure featuring a layer of six copper(II) ions sandwiched between two cyclic (PhSiO2)(6)(6-) ligands and surrounded by (BuOH)-Bu-n molecules. The magnetic properties are characterized by moderate ferromagnetic exchange interactions between the S = 1/2 copper(II) centres to give an S = 3 ground spin state. Variable temperature HF-EPR spectra evidence a hard-axis magnetic anisotropy with g(u) = 2.063, g(perpendicular to) = 2.225 and D = 0.31 cm(-1). The cage is very soluble in organic solvents and, upon exchange of the labile (BuOH)-Bu-n ligands, it functions as a high-spin hexatopic receptor for monodentate units. Reaction with the trigonal bipyramidal copper(H) mononuclear [Cu(tmpa)CN](+) in CHCl3/MeOH solution (tmpa = tris(2-pyridylmethyl)amine) affords the decacopper(II) complex [Cu-6{(PhSiO2)(6)}(2){NCCu(tmpa)}(4)](PF6)(4), whose X-ray structure and magnetic behaviour are presented. (C) 2003 Academie des Sciences. Published by Editions scientifiques et medicales Elsevier SAS. All rights reserved.