A hexanuclear heterometallic cluster of composition [Dy2 Co4 (L)4 (NO3 )2 (OH)4 (C2 H5 OH)2 ] ⋅ 2 C2 H5 OH (1) was synthesized by employing a Schiff base 2-(((2-hydroxy-3-methoxybenzyl) imino)methyl)-4-methoxyphenol (H2 L) as ligand and utilizing Dy(NO3 )3 ⋅ 6H2 O and Co(NO3 )2 ⋅ 6H2 O as metal ion sources. X-ray single-crystal diffraction analysis indicated that complex 1 contains a defect tetracubane core and possesses central symmetric structure, with two DyIII ions being in the central body position of the molecule and four CoII ions being arranged at the outer sites. Magnetic studies reveal that complex 1 behaves as single-molecule magnet (SMM) with energy barrier of 27.50 K. To investigate the individual contribution of DyIII and CoII ions to the SMM behavior, another two complexes of formulae [Dy2 Zn4 (L)4 (NO3 )2 (OH)4 ] ⋅ 4CH3 OH (2) and [Y2 Co4 (L)4 (NO3 )2 (OH)4 (C2 H5 OH)2 ] ⋅ 2 C2 H5 OH (3) were prepared. Complexes 1 and 3 are isomorphous. The coordination geometries of DyIII ions in 1 and 2 are different. The DyIII ions are eight-coordinated in 2 and nine-coordinated in 1. Complex 2 exhibits SMM behavior with energy barrier of 69.67 K, but complex 3 does not display SMM property. These results reveal that the SMM behaviors of 1 and 2 are mainly originated from DyIII ions. It might be the higher symmetry of DyIII ions in 2 that results in the higher energy barrier.
Keywords: energy barriers; heterobimetallic; lanthanide ions; polynuclear; single-molecule magnets.
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