Spin Switching via Targeted Structural Distortion Constantinos J. Milios, † Alina Vinslava, ‡ Wolfgang Wernsdorfer, ‡ Alessandro Prescimone, † Peter A. Wood, † Simon Parsons, † Spyros P. Perlepes, | George Christou, § and Euan K. Brechin* ,† Contribution from the School of Chemistry, The UniVersity of Edinburgh, West Mains Road, Edinburgh, EH9 3JJ, UK, Laboratoire Louis Ne ´ el-CNRS, 38042 Grenoble, Cedex 9, France, Department of Chemistry, UniVersity of Florida, GainesVille, Florida 32611-7200, and Department of Chemistry, UniVersity of Patras, 26504 Patras, Greece Received January 26, 2007; E-mail: ebrechin@staffmail.ed.ac.uk Abstract: The deliberate “stepwise” structural distortion of the [Mn III 6O2(sao)6(O2CR)2L4](S ) 4, U eff ) 28 K) family of SMMs (where sao 2- is the dianion of salicylaldoxime or 2-hydroxybenzaldeyhyde oxime and L ) MeOH, EtOH) via the use of derivatized oxime ligands and bulky carboxylates leads to a family of single-molecule magnets with larger spin ground states and enhanced blocking temperatures. Replacing sao 2- and HCO2 - in the molecule [Mn III 6O2(sao)6(O2CH)2(MeOH)4](1), with Et-sao 2- (Et-saoH2 ) 2-hydroxypropiophenone oxime) and Me3CCO2 - (pivalate), produces the complex [Mn III 6O2(Et-sao)6(O2- CCMe3)2(EtOH)5](2) that displays an S ) 7 ground state with U eff ) 30 K. Replacing Me3CCO2 - with PhCO2 - produces the complex [Mn III 6O2(Et-sao)6(O2CPh)2(EtOH)4(H2O)2](3) that displays an S ) 12 ground state with U eff ) 53 K. The ligand substitution invokes a subtle structural distortion to the core of the molecule evidenced by an increased “twisting” of the oxime moiety (Mn-N-O-Mn) and a change in carboxylate ligation, which, in turn, invokes a dramatic change in the observed magnetic properties by switching weak antiferromagnetic exchange to weak ferromagnetic exchange. Introduction When inorganic chemistry finally emerged as a distinct discipline in the 1950s, one of the driving forces was the application of physical methods to discover molecular structures and to determine the details of their electronic structures, so providing the basis for correlations between structure and properties. Among the methods that came into prominence at that time was the measurement of bulk magnetic susceptibility. 1 In the 1950s and 1960s it was Nyholm, 2 and Figgis and Lewis 3 who pioneered the field that became known as magnetochem- istry. However, there is now a distinct field of study developing around the directed synthesis of new molecular compounds (often based on coordination complexes) that show varieties of magnetic behavior, the so named molecular magnetism. 4 Mo- lecular magnetism designates a multidisciplinary field of research that focuses on the employment of molecular ap- proaches to design, create, study, and use new classes of magnetic materials in which properties can be tuned at the molecular level. In the past two decades this field has rapidly evolved 5 from the design of new molecule-based magnets possessing higher critical temperatures, toward the development of more complex magnetic materials with one or more functional properties of interest (bistable magnetic materials with switching properties or multifunctional materials coupling magnetism with a second property), to the synthesis and investigation of nanosized magnetic molecules and other nanostructures exhibit- ing quantum effects, and finally to materials processing aimed at application. An extensive class of nanosized magnetic molecules of great current interest are single-molecule magnets (SMMs). SMMs 6 are molecular transition-metal clusters that can retain magnetization in the absence of a magnetic field below a blocking temperature without the need for long-range coopera- tive interaction. They represent the smallest possible magnetic storage device, which can potentially retain information in a single molecule rather than in a magnetic particle or array of particles. SMMs thus represent a molecular (or bottom-up approach) to nanoscale magnets and, thus, are significantly different from classical (or top-down) nanoscale magnets of metals, metal alloys, and metal oxides. These differences include crystallinity, solubility, monodispersity, and the existence of peripheral organic ligands that prevent communication between the magnetic cores of neighboring molecules and which can be varied using chemical methods. Such molecules straddle the † The University of Edinburgh. ‡ Laboratoire Louis Ne ´el-CNRS. § University of Florida. | University of Patras. (1) Day P. J. Chem. Soc., Dalton Trans. 1997, 701. (2) Nyholm, R. S.; Tobe, M. L. AdV. Inorg. Chem. Radiochem. 1963, 5, 1. (3) For example, see: Figgis, B. N.; Lewis, J. In Modern Coordination Chemistry; Lewis, J., Wilkins, R. G., Eds.; Interscience: New York, 1960; Chapter 6. (4) Kahn, O. Molecular Magnetism; Wiley-VCH: New York, 1993. (5) Coronado, E; Gatteschi, D. J. Mater. Chem. 2006, 16, 2515 (Editorial). (6) For reviews, see: (a) Aromi, G.; Brechin, E. K. Struct. Bonding 2006, 122, 1. (b) Christou, G.; Gatteschi, D.; Hendrickson, D. N.; Sessoli, R. MRS Bull. 2000, 25, 66. (c) Gatteschi, D.; Sessoli, R. Angew. Chem., Int. Ed. 2003, 42, 268. (d) Bircher, R.; Chaboussant, G.; Dobe, C.; Gu ¨del, H. U.; Ochsenbein, S. T.; Sieber, A.; Waldman, O. AdV. Funct. Mater. 2006, 16, 209. Published on Web 04/26/2007 10.1021/ja070411g CCC: $37.00 © 2007 American Chemical Society J. AM. CHEM. SOC. 2007, 129, 6547-6561 9 6547