Chemical functionalization is a powerful approach to tailor the physical and chemical properties of two-dimensional (2D) materials, increase their processability and stability, tune their functionalities and, even, create new 2D materials. This is typically achieved through post-synthetic functionalization by anchoring molecules on the surface of an exfoliated 2D crystal, but it inevitably alters the long-range structural order of the material. Here we present a pre-synthetic approach that allows the isolation of crystalline, robust and magnetic functionalized monolayers of coordination polymers. A series of five isostructural layered magnetic coordination polymers based on Fe(ii) centres and different benzimidazole derivatives (bearing a Cl, H, CH3, Br or NH2 side group) were first prepared. On mechanical exfoliation, 2D materials are obtained that retain their long-range structural order and exhibit good mechanical and magnetic properties. This combination, together with the possibility to functionalize their surface at will, makes them good candidates to explore magnetism in the 2D limit and to fabricate mechanical resonators for selective gas sensing.
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The authors acknowledge financial support from the European Comission (COST Action MOLSPIN CA15128, FET-OPEN 2D-INK 664878, ERC-2016-CoG 724681-S-CAGE and ERC-2018-AdG 788222 Mol-2D), the Spanish MINECO (Structures of Excellence María de Maeztu MDM-2015–0538 and Severo Ochoa SEV-2012-0267, projects CTQ2014-59209-P, CTQ2017-89528-P, MAT2017-89993-R, MAT2015-68200-C2-2-P and MAT2015-71842-P), the Generalitat Valenciana (Prometeo programme) and the VLC/Campus Program. G.M.E. thanks the Spanish MINECO for a Ramón y Cajal Fellowship. S.M.V. thanks MINECO for a predoctoral FPU grant (FPU14/04407). J.L.C. acknowledges the University of Valencia for an ‘Atracció de Talent’ grant. The C2TN/IST authors acknowledge the Portuguese Foundation for Science and Technology (FCT, contract UID/Multi/04349/2013). D.D., P.G.S. and H.S.J.v.d.Z. acknowledge the support of the Netherlands Organisation for Scientific Research (NWO/OCW), as part of the Frontiers of Nanoscience (NanoFront) programme and the European Union Seventh Framework Programme under grant agreement no. 604391 Graphene Flagship. The authors thank the Spanish CRG-D1B at Institut Laue-Langevin for allocated beamtime (project CRG-2402).
Additional synthesis and characterization data; Supplementary Figures 1–45; Supplementary references 1–17
CIF for compound MUV-1-Cl; CCDC reference: 1582350
CIF for compound MUV-1-H; CCDC reference: 1582348
CIF for compound MUV-1-CH3; CCDC reference: 1582347
CIF for compound MUV-1-Br; CCDC reference: 1849147
CIF for compound MUV-1-NH2; CCDC reference: 1582349
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Nature Reviews Materials (2018)