title: Reversible switching from antiferro- to ferromagnetic behavior by solvent-mediated, thermally-induced phase transitions in a trimorphic MOF-based magnetic sponge system.
abstract: 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·0.5C6H14·0.5H2O (1), [Cu(tzc)(dpp)]n·4.5H2O (2), and [Cu(tzc)(dpp)]n·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·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·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.
authors: Department of Chemistry, Texas A&M University, 3255 TAMU College Station, Texas 77843-3255, USA.
authors: Mario
authors: M
authors: Wriedt
authors: Andrey A
authors: AA
authors: Yakovenko
authors: Gregory J
authors: GJ
authors: Halder
authors: Andrey V
authors: AV
authors: Prosvirin
authors: Kim R
authors: KR
authors: Dunbar
authors: Hong-Cai
authors: HC
authors: Zhou
mesh_terms: D003300:Copper / Q000737:chemistry; D018360:Crystallography, X-Ray; D005296:Ferrous Compounds / Q000737:chemistry*; D060526:Magnetic Fields; D008958:Models, Molecular; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D044367:Phase Transition; D012997:Solvents / Q000737:chemistry; D013696:Temperature
chemical_list: D005296:Ferrous Compounds; D009942:Organometallic Compounds; D012997:Solvents; D003300:Copper