Probing magnetic interactions in metal–organic frameworks and coordination polymers microscopically

Abstract

Materials with magnetic interactions between their metal centres play a tremendous role in modern technologies and can exhibit unique physical phenomena. In recent years, magnetic metal-organic frameworks and coordination polymers have attracted significant attention because their unique structural flexibility enables them to exhibit multifunctional magnetic properties or unique magnetic states not found in the conventional magnetic materials, such as metal oxides. Techniques that enable the magnetic interactions in these materials to be probed at the atomic scale, long established to be key for developing other magnetic materials, are not well established for studying metal-organic frameworks and coordination polymers. This review focuses on studies where metal-organic frameworks and coordination polymers have been examined using such microscopic probes, with a particular focus on neutron scattering and density-functional theory, the most-well established experimental and computational techniques for understanding magnetic materials in detail. This paper builds on a brief introduction to these techniques to describe how such probes have been applied to a variety of magnetic materials starting with select historical examples before discussing multifunctional, low dimensional and frustrated magnets. This review highlights the information that can be obtained from such microscopic studies, including the strengths and limitations of these techniques. The article then concludes with a brief perspective on the future of this area.

Emergent magnetic order and correlated disorder in formate metal-organic frameworks

“…There are much fewer detailed studies of the microscopic magnetic phases in MOFs, which typically require neutron based techniques to characterise in detail. [41] Examples of exotic magnetism in MOFs are present in the literature including chiral, 2D and 1D magnetic structures, in addition to long range magnetically ordered systems. [41] Frustrated magnetism has been experimentally studied in magnetic MOFs in materials such as Co 3 (OH) 2 (sq) 2 .3H 2 O and M(tca) 2 (tca = tricyanomide), using neutron scattering but these materials undergo phase transitions to 3D long-range ordered structures, at low temperature.…”

Ferromagnetic Ising chains in frustrated LnODCO3: the influence of magnetic structure in magnetocaloric frameworks

“…The utility of neutron diffraction for probing magnetic interactions is well known 25 but it has been highlighted recently for materials containing molecular building blocks. [26][27][28] To establish a clear understanding of how the microscopic interactions of LnOHCO 3 affect their magnetocaloric entropy change we have studied these compounds using neutron diffraction. We have established both the local magnetic correlations in these materials in their short ranged ordered phases, in which they exhibit their magnetocaloric properties, and in the case of HoOHCO 3 the long range ordered magnetic states they exhibit at low temperatures.…”

In situ observation of the magnetocaloric effect through neutron diffraction in the Tb(DCO2)3 and TbODCO3 frameworks

“…8,33 We have previously established the magnetic states that form in both Tb(HCO 2 ) 3 and TbOHCO 3 in the absence of applied magnetic fields. 9,35 Tb(HCO 2 ) 3 , which adopts R3m rhombohedral symmetry at all measured temperatures, 36 shows strong diffuse scattering indicative of short range order below 20 K, where its magnetocaloric effect begins to be significant. This short range order is formed of ferromagnetically coupled linear chains of Isinglike moments aligned along the c-axis, antiferromagnetically coupled in a triangular array within the ab plane.…”