Extended Solids Containing Periodic Arrays of Transition-Metal Oxide Magnetic Nanostructures

Wendy L. Queen (Clemson University)

Transition-metal oxide (TMO) compounds are attractive due to their structural versatility and unique chemical and physical properties, including superconductivity, ferroelectricity, nonlinear optical behavior, ionic conductivity and catalytic activity.1 Incorporation of TMOs with unpaired d-electrons can give rise to magnetic materials of fundamental and technological importance. Over the last two decades, much research has been focused in the area of molecular-based magnetic solids, such as single-molecule magnets (SMMs) and single-chain magnets (SCMs). These materials have organic-based nonmagnetic ligands allowing structural confinement of the TMO clusters and chains, respectively. Due to the low-dimensional nature of these materials and large magnetic anisotropy, they often exhibit slow relaxation of magnetization resulting in hysteresis, a phenomenon that, until the early 90.s, was associated only with bulk magnetic materials.2 From these molecular-based magnets we have learned that compounds containing finite numbers of coupled paramagnetic centers can also exhibit unusual quantum behaviour.3 It is thought that comparable magnetic properties can be achieved in extended solids containing low-dimensional magnetic nanostructures.4 In order to create structural and electronic confinement of the TMO units, rigid nonmagnetic, inorganic oxyanions, XOnm-, (where X can be a fully oxidized early transition metal, such as V5+, or a neighboring main-group element such as P, Si, or As) are utilized. High-temperature, molten-salt methods are employed to grow large single crystals of these refractory oxides for structure and property characterization. Recent results have shown that the inclusion of molten salt can also aid in the formation of low-dimensional frameworks5 such as high nuclearity TMO clusters. TMO polyhedra can link through a variety of different bridging modes (.2, .3, .4, etc.) giving rise to extended solids having very complex magnetic properties. Structural versatility found within this system has led to a large number of interesting framework formations including those containing triangular-based magnetic lattices. In this seminar I will discuss high-temperature, solid-state synthesis, and the structure and properties of some newly synthesized extended solids containing low-dimensional magnetic nanostructures.

References

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2.(a) Friedman, J. R.; Sarachik, M.P.; Tejada, J.; Ziolo, R. Phys. Rev. Lett. 1996, 76, 3830-3833. (b) Thomas, L; Lionti, F.; Ballour, R.; Gatteschi, D.; Sessoli, R.; Barbara, B. Nature. 1996, 383, 145-147. (c) Wernsdorfer, W.; Aliaga-Alcalde, N.; Hendrickson, D. N.; Christou, G. Nature. 2002, 416, 406-409. (d) Tasiopoulos, A. J.; Vinslava, A.; Wernsdorfer, W.; Abboud, K. A,; Christou, G. Angew. Chem. Int. Ed. 2004, 43, 2117- 2121. (e) Murugesu, M.; Habrych, M.; Wernsdorfer, W.; Abboud, K. A.; Christou, G. J. Am. Chem. Soc. 2004, 126, 4766-4767.

3.Gatteschi, D.; Sessoli R. Angew. Chem. Int. Ed. 2003, 42, 268-297.

4.(a) Hwu, S.-J. Chem. Mater. 1998, 10, 2846-2859. (b) Hwu, S.-J.; Ulutagay-Kartin, M.; Clayhold, J. A.; Mackay, R.; Wardojo, T. A.; O'Connor, C. T.; Krawiec, M. J. Am. Chem. Soc., 2002, 124, 12404-12405. (c) Ranmohotti, K.G S.; Mo, X; Smith, K. M.; Hwu, S.-J. Inorg. Chem., 2006, 45, 3665-3670.

5.Queen, W. L.; West, J. P.; Hwu, S.-J.; VanDerveer, D. G.; Zarzyczny, M. C.; Pavlick, R. A. Angew. Chem. Int. Ed. 2008, 47, 3791-3794.

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