The search for cobalt single-molecule magnets: A disk-like Co IIICoII 6 cluster with a ligand derived from a novel transformation of 2-acetylpyridine

Abstract

The initial employment of 2-acetylpyridine, (py)(Me)CO, in Co cluster chemistry is reported, and the synthesis, crystal structure, and full magnetic study of [Co7(OH)6(L)6](ClO4) 3·1.6H2O (1·1.6H2O) are described

L- is the anion of 2-(pyridine-2-yl)pentane-2-ol-4-one, (py)(Me)C(CH2COCH3)(O)-, formed in situ through a crossed-aldol reaction in acetone under strongly basic conditions. The reaction of Co(ClO4)2·6H2O, (py)(Me)CO and NBun 4OMe (1:1:1.2) in acetone at room temperature under aerobic conditions affords 1·1.6H2O in 35% yield. The mixed-valent cation possesses a wheel-shaped (or disk-like) structural motif comprising a central octahedral CoIII atom linked to six peripheral distorted octahedral CoII atoms by six μ3- ΟΗ- groups

the six CoII atoms on the rim are held together by six η1:η1:η1: μ2·L- ligands and the oxygen atoms of the hydroxo groups. Variable-temperature, solid-state dc and ac magnetic susceptibility studies were carried out on 1. The dc magnetic study of 1 shows a decline in the product χΜT with decreasing T. The observation of out-of phase (χ″Μ) ac susceptibility signals below ∼4 K suggests that the CoIIICoII 6 complex may be a single molecule magnet, and this was confirmed by single-crystal magnetization vs. dc field sweeps down to 0.04 K that exhibited hysteresis. The study reveals that each complex cation is a weak single-molecule magnet, but that there are also intermolecular interactions (also confirmed crystallographically) to create a 3D ordered lattice

this still gives some hysteresis at 5 K. © 2011 Elsevier B.V. All rights reserved.