Low-Dimensional Magnetism in Multivariate Copper/Zinc MOF-74 Materials Formed via Different Mechanochemical Methods

Abstract

MOF-74 is an archetypal magnetic metal−organic framework (MOF) family, with metal nodes bridged by 2,5dioxido-1,4-benzenedicarboxylic acid (H 4 dobdc) and arranged into one of the simplest representations of the 1D Ising magnetic model. Recently, a novel mechano-synthetic approach opened a pathway toward a series of bimetallic multivariate (1:1) M1M2-MOF-74 materials, with the uniform distribution of metal cations in the oxometallic chains, offering a unique opportunity to investigate low-dimensional magnetism in these heterometallic MOFs. We explore here how different mechanochemical procedures affect the interaction between the metal nodes of the model system of three multivariate copper(II)/zinc(II)-MOF-74 materials, two of which were obtained through a template-controlled procedure, and the third one was obtained by recently developed mechanical MOF-alloying combined with subsequent accelerated aging. While the three Cu/Zn-MOF-74 products have almost identical powder X-ray diffraction (PXRD) diffractograms and Fourier transform infrared spectra, they differ significantly in their magnetic properties, as revealed through detailed magnetization and X-band and multifrequency high-field electron spin resonance measurements. The magnetic results of the three multivariate Cu/Zn-MOF-74s were compared to the properties of the monometallic Cu-MOF-74, which shows antiferromagnetic intrachain and weaker ferromagnetic interchain interactions. Energy-dispersive X-ray spectroscopy/scanning electron microscopy and solid-state nuclear magnetic resonance spectroscopy helped rationalize the observed differences in magnetization, and in situ synchrotron PXRD monitoring of template-controlled MOF formation revealed different reaction pathways when using the zinc or copper intermediates, involving even the fleeting occurrence of a rare MOF-74 polymorph.

Fixing CO2 under Atmospheric Conditions and Dual Functional Heterogeneous Catalysis Employing Cu MOFs: Polymorphism, Single-Crystal-to-Single-Crystal (SCSC) Transformation and Magnetic Studies

“…The χ M T value at room temperature is found to be 0.80 cm 3 mol –1 , which is higher than the expected value for one Cu­(II) center (0.37 cm 3 mol –1 for g = 2.0). Comparable values have been reported for the other copper-containing compounds in the literature. − It may be noted that all of the copper centers in the compounds are connected by organic linkers, which are conjugated. This suggests that the copper centers may interact with each other, which would be expected to give a greater-than-expected value of 0.37 cm 3 mol –1 for the isolated Cu­(II) center.…”

Simplifying the Synthesis of Metal–Organic Frameworks

“…Previously reported mechanochemical syntheses of M 2 (dobdc) analogs have primarily involved LAG of a basic metal oxide or acetate salt and the organic linker H 4 dobdc in the presence of a small amount of solvent such as DMF, water, or methanol . Among these frameworks, only the mechanochemical synthesis of Zn 2 (dobdc) has been studied in detail . In traditional solvothermal syntheses, the role of the amide solvent is to decompose at high temperatures (>100 °C) to produce amines (e.g., N , N -dimethylamine) that deprotonate the conjugate acid of the linker prior to MOF formation.…”

“…36 Among these frameworks, only the mechanochemical synthesis of Zn 2 (dobdc) has been studied in detail. 37 In traditional solvothermal syntheses, the role of the amide solvent is to decompose at high temperatures (>100 °C) to produce amines (e.g., N,N-dimethylamine) that deprotonate the conjugate acid of the linker prior to MOF formation. Thus, we envisioned that disentangling the metal salt and base via the use of an exogenous liquid base could enable access to higher-quality materials by improving their reversible self-assembly.…”

Magnetic and optoelectronic modulation of Cu-MOF-74 films by quantum dots

“…25,26 Son et al found that the magnetic state of MOF-74 changed from ferromagnetic (FM) or antiferromagnetic (AFM) to superparamagnetic by exchanging Fe, Co and Ni in the metal clusters. 27 Megumi et al systematically studied different ratios of mixed metal Co x Ni 1− x –MOF-74 [Co 2 x Ni 2(1− x ) (dhtp), where H 4 dhtp = 2,5-dihydroxyterephthalic acid] and confirmed that their mixed-metal MOF exhibited weak ferromagnetic (tilted antiferromagnetic) behavior. 28 Besides, because of the formation of planar π-d conjugation and π–π stacking in the MOF-74 molecule, the highly delocalized π-electrons lead to local spin interactions, which result in long-range magnetic ordering and good charge mobility.…”