Highly Anisotropic Rhenium(IV) Complexes: New Examples of Mononuclear Single-Molecule Magnets

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• 作者：Jos茅 Mart铆nez-Lillo ; Teresa F. Mastropietro ; Elsa Lhotel ; Carley Paulsen ; Joan Cano ; Giovanni De Munno ; Juan Faus ; Francesc Lloret ; Miguel Julve ; Saritha Nellutla ; J. Krzystek
• 刊名：Journal of the American Chemical Society
• 出版年：2013
• 出版时间：September 18, 2013
• 年：2013
• 卷：135
• 期：37
• 页码：13737-13748
• 全文大小：553K
• 年卷期：v.135,no.37(September 18, 2013)
• ISSN：1520-5126

文摘

The rhenium(IV) complex (NBu₄)₂[ReBr₄(ox)] (1) (ox = oxalate and NBu₄⁺ = tetra-n-butylammonium cation) has been prepared and its crystal structure determined by X-ray diffraction. The structure is made up of discrete [ReBr₄(ox)]^{2鈥?/sup> anions and bulky NBu₄+ cations. Each [ReBr₄(ox)]2鈥?/sup> anion is surrounded by six NBu₄+ cations, which preclude any significant intermolecular contact between the anionic entities, the shortest rhenium路路路rhenium distance being 9.373(1) 脜. Variable temperature dc and ac magnetic susceptibility measurements and field-dependent magnetization experiments on polycrystalline samples of 1 reveal the occurrence of highly anisotropic magnetically isolated Re(IV) centers (S_Re = 3/2), which exhibit slow relaxation of the magnetization at very low temperatures in a dc field. Ac measurements conducted on a polycrystalline sample of the complex (NBu₄)₂[ReCl₄(ox)] (2) [compound isostructural to 1 whose structure and dc magnetic susceptibility study were previously reported in Tomkiewicz, A.; Bartczak, T. J.; Kruszy艅ski, R.; Mrozi艅ski, J. J. Mol. Struct. 2001, 595, 225] show a similar behavior, both complexes thus constituting new examples of mononuclear single-molecule magnets. High-frequency and -field electron paramagnetic resonance on polycrystalline samples of 1 and 2 and on single crystals of 2 allowed for the determination for the first time of the negative sign and confirmed a significant magnitude and rhombicity (E/D) of the zero-field splitting tensor of the [ReCl₄(ox)]2鈥?/sup> and [ReBr₄(ox)]2鈥?/sup> centers, originating from a combination of spin鈥搊rbit coupling and low molecular symmetry. D and E values of 1 and 2 were estimated through magnetization measurements and theoretically calculated through complete active space and density functional theory methodologies.}