Single-Molecule Magnetism in a Family of {CoIII2DyIII2} Butterfly Complexes: Effects of Ligand Replacement on the Dynamics of Magnetic Relaxation

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• 作者：Stuart K. Langley ; Liviu Ungur ; Nicholas F. Chilton ; Boujemaa Moubaraki ; Liviu F. Chibotaru ; Keith S. Murray
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：May 5, 2014
• 年：2014
• 卷：53
• 期：9
• 页码：4303-4315
• 全文大小：859K
• 年卷期：v.53,no.9(May 5, 2014)
• ISSN：1520-510X

文摘

The synthesis and structural characterization of four related heterometallic complexes of formulas [Dy<sup>IIIsup><sub>2sub>Co<sup>IIIsup><sub>2sub>(OMe)<sub>2sub>(teaH)<sub>2sub>(O<sub>2sub>CPh)<sub>4sub>(MeOH)<sub>4sub>](NO<sub>3sub>)<sub>2sub>路MeOH路H<sub>2sub>O (1a) and [Dy<sup>IIIsup><sub>2sub>Co<sup>IIIsup><sub>2sub>(OMe)<sub>2sub>(teaH)<sub>2sub>(O<sub>2sub>CPh)<sub>4sub>(MeOH)<sub>2sub>(NO<sub>3sub>)<sub>2sub>]路MeOH路H<sub>2sub>O (1b), [Dy<sup>IIIsup><sub>2sub>Co<sup>IIIsup><sub>2sub>(OMe)<sub>2sub>(dea)<sub>2sub>(O<sub>2sub>CPh)<sub>4sub>(MeOH)<sub>4sub>](NO<sub>3sub>)<sub>2sub> (2), [Dy<sup>IIIsup><sub>2sub>Co<sup>IIIsup><sub>2sub>(OMe)<sub>2sub>(mdea)<sub>2sub>(O<sub>2sub>CPh)<sub>4sub>(NO<sub>3sub>)<sub>2sub>] (3), and [Dy<sup>IIIsup><sub>2sub>Co<sup>IIIsup><sub>2sub>(OMe)<sub>2sub>(bdea)<sub>2sub>(O<sub>2sub>CPh)<sub>4sub>(MeOH)<sub>4sub>](NO<sub>3sub>)<sub>2sub>路0.5MeOH路H<sub>2sub>O (4a) and [Dy<sup>IIIsup><sub>2sub>Co<sup>IIIsup><sub>2sub>(OMe)<sub>2sub>(bdea)<sub>2sub>(O<sub>2sub>CPh)<sub>4sub>(MeOH)<sub>2sub>(NO<sub>3sub>)<sub>2sub>]路MeOH路1.5H<sub>2sub>O (4b) are reported (teaH<sub>3sub> = triethanolamine, deaH<sub>2sub> = diethanolamine, mdeaH<sub>2sub> = N-methyldiethanolamine, and bdeaH<sub>2sub> = N-n-butyldiethanolamine). Compounds 1 (鈮?1a and 1b) and 4 (鈮?4a and 4b) both display two unique molecules within the same crystal and all compounds display a butterfly type core, with the Dy<sup>IIIsup> ions occupying the central body positions and the diamagnetic Co<sup>IIIsup> ions the outer wing-tip sites. Compounds 1鈥?b>4 were investigated via direct current and alternating current magnetic susceptibility measurements, and it was found that each complex displayed single-molecule magnet (SMM) behavior. All four compounds display unique coordination and geometric environments around the Dy<sup>IIIsup> ions and it was found that each displays a different anisotropy barrier. Ab initio calculations were performed on 1鈥?b>4 and these determined the low lying electronic structure of each Dy<sup>IIIsup> ion and the magnetic interactions for each cluster. It was found that there was a strong correlation between the calculated energy gap between the ground and first excited states of the single-ion ligand-field split Dy<sup>IIIsup> levels and the experimentally observed anisotropy barrier. Furthermore, the transverse g factors found for the Dy<sup>IIIsup> ions, defining the tunnelling rates within the ground Kramers doublets, are largest for 1, which agrees with the experimental observation of the shortest relaxation time in the high-temperature domain for this complex. The magnetic exchange between the Dy<sup>IIIsup> ions revealed overall antiferromagnetic interactions for each compound, derived from the dominant dipolar exchange resulting in nonmagnetic ground states for 1鈥?b>4. The diamagnetic ground states coupled with small tunneling gaps resulted in quantum tunneling time scales at zero field of between 0.1 and >1.5 s.