Web Release Date: September 28,
Supramolecular Copper Hydroxide Tennis Balls: Self-Assembly, Structures, and Magnetic Properties of Octanuclear [Cu8L8(OH)4]4+ Clusters (HL = N-(2-Pyridylmethyl)acetamide)
and
Department of Chemistry and Biochemistry, University of Oklahoma, 620 Parrington Oval, Norman, Oklahoma 73019, and Department of Physics, Texas A&M University, College Station, Texas 77843
Received May 24, 2004
Abstract:
The self-assembly of supramolecular copper "tennis balls" that possess unusual magnetic properties using a small
pyridyl amide ligand is described. Copper(II) complexes of N-(2-pyridylmethyl)acetamide (HL) were synthesized in
methanol. In the absence of base, the mononuclear complex [Cu(HL)2](ClO4)2 (1) was prepared. The structure of
1, determined by X-ray crystallography, contains a copper(II) ion surrounded by bidentate HL ligands coordinated
via the pyridyl N atom and the carbonyl O atom in a trans, square planar arrangement. Reactions carried out in
the presence of triethylamine resulted in cluster complexes [Cu8L8(OH)4](ClO4)4 and [Cu8L8(OH)4](CF3SO3)4 [2(ClO4)4
and 2(OTf)4, respectively]. The cationic portions of 2(ClO4)4 and 2(OTf)4 are isostructural, containing eight copper(II)
ions, eight deprotonated ligands (L-), and four 
3-hydroxide ligands. The top and bottom halves of the cluster are
related by a pseudo-S4 symmetry operation and are held together by bridging L- ligands. Solutions of 2(ClO4)4 and
2(OTf)4, which were shown to contain the full [Cu8L8(OH)4]4+ fragment by electrospray mass spectrometry and
conductance experiments, are EPR silent. Magnetic susceptibility measurements for 2(ClO4)4 as a function of
temperature and magnetic field showed the Cu ions all to exhibit magnetic moments in the range expected for the
d9 configuration. At low temperatures, the magnetization was reduced due to predominantly antiferromagnetic
interactions between ions. Analysis showed that partially frustrated interactions among the four Cu ions making up
each half of the cluster gave good agreement with the data once a large molecular anisotropy was taken into
account, with Jc = 106 cm-1, D = 27 cm-1, and g = 2.17.
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