Rational Design of Large Spin Clusters Based on the Hexacopper(II) Siloxanolate Core

The hexacopper(II) siloxanolate cage [Cu6{(PhSiO2)6}2(BuOH)5]·3BuOH was 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)66- ligands and surrounded by BuOH mols. Two different mols. are obsd. in the crystal structure of [Cu6{(PhSiO2)6}2(BuOH)5]·3BuOH. One mol. has all six copper atoms bonded to BuOH ligands and the other has only four of the six copper atoms bonded to BuOH ligands. The magnetic properties were characterized by moderate ferromagnetic exchange interactions between the S = 1/2 copper(II) centers to give an S = 3 ground spin state. Variable temp. HF-EPR spectra evidence a hard-axis magnetic anisotropy with gpar = 2.063, gperp = 2.225 and D = 0.31 cm-1. The cage is very sol. in org. solvents and, upon exchange of the labile BuOH ligands, it functions as a high-spin hexatopic receptor for monodentate units. Reaction with the trigonal bipyramidal copper(II) mononuclear [Cu(tmpa)CN]+ in CHCl3/MeOH soln. (tmpa = tris(2-pyridylmethyl)amine) affords the decacopper(II) complex [Cu6{(PhSiO2)6}2{NCCu(tmpa)}4](PF6)4, whose x-ray structure and magnetic behavior are presented.