The search for cobalt single-molecule magnets: A disk-like (CoCo6II)-Co-III cluster with a ligand derived from a novel transformation of 2-acetylpyridine
Résumé
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 [Co-7(OH)(6)(L)(6)](ClO4)(3)center dot 1.6H(2)O (1.1.6H(2)O) 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)center dot 6H(2)O, (POMe)CO and (NBu4OMe)-O-II (1:1:1.2) in acetone at room temperature under aerobic conditions affords 1.1.6H(2)O in 35% yield. The mixed-valent cation possesses a wheel-shaped (or disk-like) structural motif comprising a central octahedral Co-III atom linked to six peripheral distorted octahedral Co-II atoms by six mu(3)-OII- groups: the six Co-II atoms on the rim are held together by six eta(1):eta(1):eta(1):mu(2).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 chi(T)(M) with decreasing T. The observation of out-of phase (chi ''(M)) ac susceptibility signals below similar to 4 K suggests that the CoIIICo6II 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. (C) 2011 Elsevier Ltd. All rights reserved.