[(Tp)(8)(H(2)O)(6)Cu(II) (6)Fe(III) (8)(CN)(24)](4+): a cyanide-bridged face-centered-cubic cluster with single-molecule-magnet behavior.

In the past decade, an increasing number of molecular clusters have been shown to exhibit magnetic bistability. These species, called single-molecule magnets (SMMs), have gained considerable attention because they retain information in a single molecule rather than in a magnetic particle or array of particles and can potentially be used in quantum computers. Furthermore, understanding the magnetic properties of these molecules is important to help bridge the gap between the quantum and classical understanding of magnetism. The most thoroughly studied SMMs are [Mn12O12(CH3CO2)16(H2O)4] and its derivatives, [4] but there are a number of other clusters containing Fe, V, Co, or Ni [8] ions that have been reported to be SMMs. These species are all homometallic systems in which magnetic exchange interactions occur through bridging oxygen atoms. Important to the future of the field of SMMs is the development of new synthetic schemes that can yield clusters with a large spin and/or anisotropy. Metal–cyanide cluster systems offer an advantage for achieving such control, through the substitution of various metal ions into a given structure type. Moreover, the nature of the magnetic exchange coupling between different metal ions in the resulting cluster is readily predicted. One approach to synthesizing high-nuclearity metal–cyanide clusters employs multidentate capping ligands to inhibit growth of an extended solid and direct the structure of the product. Many clusters have been prepared by this method, including the facecentered-cubic species [(Me3tacn)8Cr8Ni6(CN)24] 12+ (Me3tacn= N,N’,N’’-trimethyl-1,4,7-triazacyclononane) and [(tach)8(H2O)6Cu6Co8(CN)24 THF] (tach= 1,3,5-triaminocyclohexane). However, as far as we know, there are only a very few cyanide-bridged SMMs, and none of the established SMMs exhibit cubic symmetry. In an effort to extend this chemistry, we have chosen to employ the precursor compound (Bu4N)[(Tp)Fe(CN)3] (1; Tp = hydrotris(pyrazolyl)borate), featuring a low-spin Fe center octahedrally coordinated by three CN groups and the tridentate ligand Tp . This monoanionic complex has also been utilized by Julve and co-workers as the tetraphenylphosphonium salt. Tp is a classical scorpionate ligand with a C3 axis, and in contrast to neutral capping ligands, such as Me3tacn and tach, is negatively charged which should help alleviate the build-up of excessive positive charge in clusters. Thus, [(Tp)Fe(CN)3] is anticipated to direct the formation of new cyanide-bridged compounds with interesting structures and magnetic properties. Indeed, we have recently reported its use in the preparation of [(Tp)2Fe2(CN)6Cu(CH3OH)· 2CH3OH]n, a single-chain magnet with a blocking temperature of approximately 6 K. Herein, we disclose its use in the synthesis of [(Tp)8(H2O)6Cu II 6Fe III 8(CN)24] , a facecentered-cubic cluster exhibiting SMM-type behavior. The compound [(Tp)8(H2O)6Cu6Fe8(CN)24](ClO4)4· 12H2O·2Et2O (2) crystallizes in space group Immm, [16] with the well-isolated [(Tp)8(H2O)6Cu6Fe8(CN)24] 4+ molecules residing on special positions of mmm site symmetry. As shown in Figure 1, the clusters adopt a face-centered-cubic geometry, in which eight Tp -capped Fe ions are arranged in a cube and linked through cyanide to six Cu ions located just above the center of each cube face. Here, each octahedral [(Tp)Fe(CN)3] unit uses the three cyanide groups to connect with three Cu ions, which are further ligated by water to give [*] Dr. S. Wang, Prof. Dr. J.-L. Zuo, Prof. X. -Z. You Coordination Chemistry Institute State Key Laboratory of Coordination Chemistry Nanjing University Nanjing 210093 (China) Fax: (+86)25-8331-7761 E-mail: zuojl@nju.edu. cn xyz@nju.edu. cn