Inducing single-molecule magnetism in a family of loop-of-loops aggregates: Heterometallic Mn40Na4 clusters and the homometallic Mn44 analogue
Date
2010Author
Moushi, Eleni E.Lampropoulos, Christos
Wernsdorfer, W.
Nastopoulos, Vassilios
Christou, George
Tasiopoulos, Anastasios J.
Source
Journal of the American Chemical SocietyVolume
132Issue
45Pages
16146-16155Google Scholar check
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The syntheses, crystal structures, and magnetic properties of a new family of heterometallic Mn40Na4 and homometallic Mn44 loop-of-loops aggregates are reported. The reactions of [Mn3O(O 2CMe)6(py)3]•py with 1,3-propanediol (pdH2) and 2-methyl-1,3-propanediol (mpdH2) in the presence of NaN3 afforded [Mn10Na(μ3-O) 2(O2CMe)13(pd)6(py) 2]4 (1)4 and [Mn10Na(μ 3-O)2(O2CMe)13(mpd) 6(py)(H2O)]4 (2)4, respectively. Mn40Na4 complexes (1)4 and (2)4 consist of four Mn10 loops linked through Na+ ions to give a supramolecular aggregate with a saddle-like topology. Magnetic characterization of compound (1)4 showed that each Mn10 loop has an S = 4 ground-state spin and displays frequency-dependent in-phase and out-of-phase ac susceptibility signals. It also exhibits hysteresis loops that, however, are not typical of single-molecule magnets (SMMs) due to the existence of interloop interactions between the neighboring Mn10 units of (1)4 through the diamagnetic Na+ ions, and also intermolecular interactions between different Mn40Na4 aggregates. The magnetically discrete Mn44 analogue was targeted with high priority and finally prepared from the reaction of [Mn3O(O 2CMe)6(py)3]•py with pdH2 in the presence of Mn(ClO4)2•6H2O. The loop-of-loops structure of [Mn44(μ3-O) 8(O2CMe)52(pd)24(py) 8](ClO4)(OH)3 (3) is essentially identical to those of (1)4 and (2)4, with the most significant difference being that the four Na+ ions of (1)4 and (2)4 have been replaced with Mn2+ ions. Compound 3 is thus best described magnetically as a Mn44 cluster. In accord with this description and the stronger exchange coupling between the four Mn10 loops expected through the connecting Mn2+ ions, magnetic susceptibility measurements revealed that 3 has an S = 6 ground-state spin and displays frequency-dependent in-phase and out-of-phase ac signals. Magnetization vs dc field sweeps on single-crystals of 3 displayed scan rate- and temperature-dependent hysteresis loops confirming that complex 3 is a new SMM, and is thus the second largest Mn cluster and SMM reported to date. © 2010 American Chemical Society.
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