Single‐Molecule Magnet Behavior of Individual Polyoxometalate Molecules Incorporated within Biopolymer or Metal–Organic Framework Matrices

Abstract

The chemically and structurally highly stable polyoxometalate (POM) single-molecule magnet (SMM) [(FeW9 O34 )2 Fe4 (H2 O)2 ](10-) (Fe6 W18 ) has been incorporated by direct or post-synthetic approaches into a biopolymer gelatin (Gel) matrix and two crystalline metal-organic frameworks (MOFs), including one diamagnetic (UiO-67) and one magnetic (MIL-101(Cr)). Integrity of the POM in the Fe6 W18 @Gel, Fe6 W18 @UiO-67 and Fe6 W18 @MIL-101(Cr) composites was confirmed by a set of complementary techniques. Magnetic studies indicate that the POMs are magnetically well isolated. Remarkably, in Fe6 W18 @Gel, the SMM properties of the embedded molecules are close to those of the crystals, with clear quantum tunneling steps in the hysteresis loops. For the Fe6 W18 @UiO-67 composite, the molecules retain their SMM properties, the energy barrier being slightly reduced in comparison to the crystalline material and the molecules exhibiting a tunneling rate of magnetization significantly faster than for Fe6 W18 @Gel. When Fe6 W18 is introduced into MIL-101(Cr), the width of the hysteresis loops is drastically reduced and the quantum tunneling steps are smeared out because of the magnetic interactions between the antiferromagnetic matrix and the SMM guest molecules.

A Multifunctional Dual-Luminescent Polyoxometalate@Metal-Organic Framework EuW10@UiO-67 Composite as Chemical Probe and Temperature Sensor

“…Such materials have shown their efficiency for catalytic reactions ranging from the oxidation of alkylbenzene (Sun et al, 2016 ) to the C-H activation of nitrile (Shi et al, 2016 ) and water oxidation (Mukhopadhyay et al, 2018 ; Paille et al, 2018 ). Interestingly, it has also been shown that a single-molecule magnet iron POM isolated in the cavities of a diamagnetic MOF preserves its magnetic properties (Salomon et al, 2016 ). Besides, while Ln-MOFs and Ln-doped MOFs have been largely studied, the encapsulation of a well-defined inorganic luminescent compound in MOFs for sensing and detection has been rarely described (Cui et al, 2015 ; Wu et al, 2017 ).…”

Zinc‐Substituted Polyoxotungstate@amino‐MIL‐101(Al) – An Efficient Catalyst for the Sustainable Desulfurization of Model and Real Diesels

“…In general, heterogeneous catalytic processes are preferred, as they allow easier catalyst recovery and recycling, which is of significant industrial interest. One well‐explored strategy to convert homogeneous POM catalysts to heterogeneous ones revolves around their encapsulation within porous solid supports, such as porous oxides and metal–organic frameworks (MOFs) . MOFs are particularly well‐suited as host materials for POMs owing to their crystalline open structures, varying pore volumes and surface areas, tunable functionality, and, in certain cases, high thermal, chemical, and hydrolytic stabilities.…”

Magnetic functionalities in MOFs: from the framework to the pore

“…116 Thus, the internal magnetic field created by the long-range magnetic ordering of the MOF seems to have an influence on the slow magnetic relaxation of the SIM leading to an attenuation of the quantum tunneling of the magnetization in the mononuclear complex. Non-magnetic MOFs have also been used to accommodate the magnetic molecules with 118 In the diamagnetic matrix the SMM behavior is retained because the magnetic anisotropy of the POMs is not altered by their interaction with the host. Differently, in the antiferromagnetic matrix the SMM character is clearly reduced because the magnetic interactions lead to faster relaxation of the magnetization.…”