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.

Magnetic functionalities in MOFs: from the framework to the pore

“…9. 39 The parent compound, [Cu(tzc)(dpp)]Á2H 2 O, can lose one equivalent of water to form the monohydrate phase, [Cu(tzc)(dpp)]ÁH 2 O, or can also transform into an anhydrous phase [Cu(tzc)(dpp)], which can exist in three different polymorphs. The dihydrate phase shows antiferromagnetic exchange interactions, whereas ferromagnetic properties are observed for the trimorphic anhydrate system.…”

Pressure inverse solubility and polymorphism of an edible γ-cyclodextrin-based metal–organic framework

“…However, it is characteristic of transforming MOFs that some transport of guest molecules will be involved, and such different MOF structures are treated as polymorphs. 24,25 The cubic form a of the space group I432 is retained during the compression up to at least 1.76 GPa, when the crystal dissolves (Fig. 7).…”

Crystalline central-metal transformation in metal-organic frameworks

“…Host-guest interactions can cause perturbations that lead to a switch in the spin state at constant (ideally ambient) temperature, but without disrupting the framework structure [50]. Alterations of guest molecules significantly change intermolecular cooperative interactions, which play important roles in the tuning of SCO behaviors [51][52][53][54][55].…”