Reversible Switching from Antiferro- to Ferromagnetic Behavior by Solvent-Mediated, Thermally-Induced Phase Transitions in a Trimorphic MOF-Based Magnetic Sponge System

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• 作者：Mario Wriedt ; Andrey A. Yakovenko ; Gregory J. Halder ; Andrey V. Prosvirin ; Kim R. Dunbar ; Hong-Cai Zhou
• 刊名：The Journal of the American Chemical Society
• 出版年：2013
• 出版时间：March 13, 2013
• 年：2013
• 卷：135
• 期：10
• 页码：4040-4050
• 全文大小：669K
• 年卷期：v.135,no.10(March 13, 2013)
• ISSN：1520-5126

文摘

Hydrothermal reactions of copper(II) acetate, tetrazolate-5-carboxylate (tzc), and the neutral N-donor spacer ligand 1,3-di(4-pyridyl)propane (dpp) lead in a single reaction vial to the simultaneous formation of three different single-crystalline solvates [Cu(tzc)(dpp)]_n路0.5C₆H₁₄路0.5H₂O (1), [Cu(tzc)(dpp)]_n路4.5H₂O (2), and [Cu(tzc)(dpp)]_n路1.25C₆H₁₄ (3). All three structures were characterized by single crystal X-ray diffraction. None of these solvates can be prepared as phase-pure bulk materials, but reaction conditions similar to those used for single crystal synthesis yield a phase-pure polycrystalline bulk material of an additional forth solvate phase [Cu(tzc)(dpp)]_n路2H₂O (4). Investigations of its thermal properties by in situ temperature-dependent synchrotron-based powder diffraction experiments have shown interesting phase transitions upon heating in a helium stream. Initially, the precursor dihydrate 4 transforms to an anhydrous phase [Cu(tzc)(dpp)]_n (6I) via the intermediate monohydrate phase [Cu(tzc)(dpp)]_n路H₂O (5). Upon further heating, phase 6I transforms to a new anhydrous polymorph 6II, which transforms upon cooling to a further new phase 6III. Thermogravimetric measurements performed in tandem with differential scanning calorimetry as well as infrared spectroscopic investigations are in agreement with these findings. The de/resolvation behavior is accompanied by a dramatic change in their magnetic properties: The dihydrate phase shows antiferromagnetic exchange interactions, whereas ferromagnetic properties are observed for the trimorphic anhydrate system. This magnetic sponge-like behavior can be reversibly cycled upon de/resolvation of the material.