Inducing Single-Molecule Magnetism in a Family of Loop-of-Loops Aggregates: Heterometallic Mn40Na4 Clusters and the Homometallic Mn44 Analogue

Abstract

The syntheses, crystal structures, and magnetic properties of a new family of heterometallic Mn(40)Na(4) and homometallic Mn(44) loop-of-loops aggregates are reported. The reactions of [Mn(3)O(O(2)CMe)(6)(py)(3)]·py with 1,3-propanediol (pdH(2)) and 2-methyl-1,3-propanediol (mpdH(2)) in the presence of NaN(3) afforded [Mn(10)Na(μ(3)-O)(2)(O(2)CMe)(13)(pd)(6)(py)(2)](4) (1)(4) and [Mn(10)Na(μ(3)-O)(2)(O(2)CMe)(13)(mpd)(6)(py)(H(2)O)](4) (2)(4), respectively. Mn(40)Na(4) complexes (1)(4) and (2)(4) consist of four Mn(10) loops linked through Na(+) ions to give a supramolecular aggregate with a saddle-like topology. Magnetic characterization of compound (1)(4) showed that each Mn(10) 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 Mn(10) units of (1)(4) through the diamagnetic Na(+) ions, and also intermolecular interactions between different Mn(40)Na(4) aggregates. The magnetically discrete Mn(44) analogue was targeted with high priority and finally prepared from the reaction of [Mn(3)O(O(2)CMe)(6)(py)(3)]·py with pdH(2) in the presence of Mn(ClO(4))(2)·6H(2)O. The loop-of-loops structure of [Mn(44)(μ(3)-O)(8)(O(2)CMe)(52)(pd)(24)(py)(8)](ClO(4))(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 Mn(2+) ions. Compound 3 is thus best described magnetically as a Mn(44) cluster. In accord with this description and the stronger exchange coupling between the four Mn(10) loops expected through the connecting Mn(2+) 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.