Chemical Design and Magnetic Ordering in Thin Layers of 2D Metal-Organic Frameworks (MOFs).

Javier López-Cabrelles,Peter G Steeneken,Guillermo Mínguez Espallargas,Makars Šiškins,Samuel Mañas-Valero,Martin Lee,Herre S J Van Der Zant,Eugenio Coronado,Iñigo J Vitórica-Yrezábal

doi:10.1021/jacs.1c07802

Abstract

Through rational chemical design, and thanks to the hybrid nature of metal–organic frameworks (MOFs), it is possible to prepare molecule-based 2D magnetic materials stable at ambient conditions. Here, we illustrate the versatility of this approach by changing both the metallic nodes and the ligands in a family of layered MOFs that allows the tuning of their magnetic properties. Specifically, the reaction of benzimidazole-type ligands with different metal centers (MII = Fe, Co, Mn, Zn) in a solvent-free synthesis produces a family of crystalline materials, denoted as MUV-1(M), which order antiferromagnetically with critical temperatures that depend on M. Furthermore, the incorporation of additional substituents in the ligand results in a novel system, denoted as MUV-8, formed by covalently bound magnetic double layers interconnected by van der Waals interactions, a topology that is very rare in the field of 2D materials and unprecedented for 2D magnets. These layered materials are robust enough to be mechanically exfoliated down to a few layers with large lateral dimensions. Finally, the robustness and crystallinity of these layered MOFs allow the fabrication of nanomechanical resonators that can be used to detect—through laser interferometry—the magnetic order in thin layers of these 2D molecule-based antiferromagnets.

Highlights

The isolation of atomically thin single or few-layer crystals has given rise to the emergence of the so-called twodimensional (2D) materials
At the intersection between the fields of molecular magnetism and 2D materials, we have exploited the chemical design of layered magnetic coordination polymers based on benzimidazole derivatives with the aim of producing novel 2D molecularbased magnets with novel topologies and tunable magnetic properties
Using a solvent-free synthetic route, we have prepared an isoreticular series of layered materials formed by van der Waals layers with a square 2D magnetic lattice, in which the magnetic properties can be tuned by changing the metallic nodes (from Fe(II) to Co(II) and Mn(II)), while preserving the same crystal structure

Summary

■ INTRODUCTION

The isolation of atomically thin single or few-layer crystals has given rise to the emergence of the so-called twodimensional (2D) materials These low-dimensional materials have shown a wide range of electronic and magnetic properties (from insulators to superconductors; from ferromagnets to antiferromagnets and quantum spin liquids) that can be affected by the dimensionality.[1−5] Most of these materials derive from well-known layered inorganic materials,[6] formed by covalently bound layers interconnected by weak van der Waals interactions, allowing the isolation of monolayers by exfoliation. The two-dimensional units are composed of covalently bound double layers held together through coordination bonds and interconnected by weak van der Waals interactions, instead of being formed by covalently bound monolayers This novel structural arrangement opens the way to isolate unprecedented 2D magnetic networks using a coordination chemistry approach. The mechanical dissipation Q 1(T) exhibits a local maximum near TN, as displayed in Figure 6j−l, that can be related to thermoelastic or other more intricate magnetomotive damping mechanism.[28]

■ CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES