Functionalization using biocompatible carboxylated cyclodextrins of iron-based nanoMIL-100

Here we report the first example of nanoMIL-100 particles modified with monomeric cyclodextrin derivatives of different length by exploiting strong interactions between non-saturated iron trimers at the external surface and carboxylate functionalities located at the end of biocompatible and flexible linkers of cyclodextrins. The main results revealed that, after the functionalization, the cyclodextrins are selectively located at the external surfaces covering the nanoparticles. Z potential measurements show that this functionalization induced changes respect to the bare nanoMIL-100 particles, however, the presence of the cyclodextrins does not modify the size neither porosity of the nanoparticles. The amount of cyclodextrins attached, investigated by thermogravimetry, increases with the length of the linker between CD cavity and nanoparticle surface, reaching up a 9 % wt. Auger spectroscopy suggested a clear predominant sp3 character after the functionalizations (vs. sp2 predominance in the unmodified nanoMIL-100). This study supposes the creation of an alternative family of hybrids based on carboxylated monomeric cyclodextrins

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

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

Metal Hydrides Form Halogen Bonds: Measurement of Energetics of Binding

The formation of halogen bonds from iodopentafluorobenzene and 1-iodoperfluorohexane to a series of bis(η5-cyclopentadienyl)metal hydrides (Cp2TaH3, 1; Cp2MH2, M = Mo, 2, M = W, 3; Cp2ReH, 4; Cp2Ta(H)CO, 5; Cp = η5-cyclopentadienyl) is demonstrated by 1H NMR spectroscopy. Interaction enthalpies and entropies for complex 1 with C6F5I and C6F13I are reported (ΔH° = −10.9 ± 0.4 and −11.8 ± 0.3 kJ/mol; ΔS° = −38 ± 2 and −34 ± 2 J/(mol·K), respectively) and found to be stronger than those for 1 with the hydrogen-bond donor indole (ΔH° = −7.3 ± 0.1 kJ/mol, ΔS° = −24 ± 1 J/(mol·K)). For the more reactive complexes 2–5, measurements are limited to determination of their low-temperature (212 K) association constants with C6F5I as 2.9 ± 0.2, 2.5 ± 0.1, <1.5, and 12.5 ± 0.3 M–1, respectively

Isoreticular two-dimensional magnetic coordination polymers prepared through pre-synthetic ligand functionalization

Chemical functionalization is a powerful approach to tailor the physical and chemical properties of two-dimensional 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 isoreticular 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

Magnetic and Photoluminescent Sensors Based on Metal-Organic Frameworks Built up from 2-aminoisonicotinate

Red Guipuzcoana de Ciencia, Tecnologia e Innovacion OF218/2018 University of Basque Country GIU 17/13 Basque Government IT1005-16 IT1291-19 IT1310-19 Junta de Andalucia FQM-394 Spanish Ministry of Science, Innovation and Universities (MCIU/AEI/FEDER, UE) PGC2018-102052-A-C22 PGC2018-102052-B-C21 MAT2016-75883-C2-1-P European Union (EU) ESFIn this work, three isostructural metal-organic frameworks based on frst row transition metal ions and 2-aminoisonicotinate (2ain) ligands, namely, {[M(μ-2ain)2]·DMF}n [MII=Co (1), Ni (2), Zn (3)], are evaluated for their sensing capacity of various solvents and metal ions by monitoring the modulation of their magnetic and photoluminescence properties. The crystal structure consists of an open diamond-like topological 3D framework that leaves huge voids, which allows crystallizing two-fold interpenetrated architecture that still retains large porosity. Magnetic measurements performed on 1 reveal the occurrence of feld-induced spin-glass behaviour characterized by a frequency-independent relaxation. Solvent-exchange experiments lead successfully to the replacement of lattice molecules by DMSO and MeOH, which, on its part, show dominating SIM behaviour with low blocking temperatures but substantially high energy barriers for the reversal of the magnetization. Photoluminescence studied at variable temperature on compound 3 show its capacity to provide bright blue emission under UV excitation, which proceeds through a ligand-centred charge transfer mechanism as confrmed by timedependent DFT calculations. Turn-of and/or shift of the emission is observed for suspensions of 3 in diferent solvents and aqueous solutions containing metal ions

Single-Crystal Epr Spectroscopy Of A Co(Ii) Single-Chain Magnet

An electron paramagnetic resonance (EPR) study of a single crystal of CoII-based single-chain magnets (SCM) is presented. Discrete resonant absorptions are associated to the presence of magnetic domains within the chains of finite lengths determined by a competition between intra-chain exchange interactions and thermally excited single spin fluctuations. The results are interpreted as a transition from single spin dynamics at high temperature (T ∼20 K), associated to the Kramers doublet ground state of the individual CoII ions, to archetypical SCM dynamics at low temperatures, where intra-chain correlations form long magnetic domains, whose average length is imposed by the concentration of defects in the sample. © 2013 Elsevier Ltd. All rights reserved

Snapshots of a solid-state transformation: Coexistence of three phases trapped in one crystal

Crystal-to-crystal transformations have been crucial in the understanding of solid-state processes, since these may be studied in detail by means of single crystal X-ray diffraction (SCXRD) techniques. The description of the mechanisms and potential intermediates of those processes remains very challenging. In fact, solid-state transient states have rarely been observed, at least to a sufficient level of detail. We have investigated the process of guest extrusion from the non-porous molecular material Fe(bpp)(H2L)](ClO4)2·1.5C3H6O (bpp = 2,6-bis(pyrazol-3-yl)pyridine; H2L = 2,6-bis(5-(2-methoxyphenyl)-pyrazol-3-yl)pyridine; C3H6O = acetone), which occurs through ordered diffusion of acetone in a crystal-to-crystal manner, leading to dramatic structural changes. The slow kinetics of the transition allows thermal trapping of the system at various intermediate stages. The transiting single crystal can be then examined at these points through synchrotron SCXRD, offering a window upon the mechanism of the transformation at the molecular scale. These experiments have unveiled the development of an ordered intermediate phase, distinct from the initial and the final states, coexisting as the process advances with either of these two phases or, at a certain moment with both of them. The new intermediate phase has been structurally characterized in full detail by SCXRD, providing insights into the mechanism of this diffusion triggered solid-state phenomenon. The process has been also followed by calorimetry, optical microscopy, local Raman spectroscopy and powder X-ray diffraction. The discovery and description of an intermediate ordered state in a molecular solid-state transformation is of great interest and will help to understand the mechanistic details and reaction pathways underlying these transformations

Snapshots of a solid-state transformation: coexistence of three phases trapped in one crystal

Crystal-to-crystal transformations have been crucial in the understanding of solid-state processes, since these may be studied in detail by means of single crystal X-ray diffraction (SCXRD) techniques. The description of the mechanisms and potential intermediates of those processes remains very challenging. In fact, solid-state transient states have rarely been observed, at least to a sufficient level of detail. We have investigated the process of guest extrusion from the non-porous molecular material [Fe(bpp)(H2L)](ClO4)2$1.5C3H6O (bpp ¼ 2,6-bis(pyrazol-3-yl)pyridine; H2L ¼ 2,6-bis(5-(2- methoxyphenyl)-pyrazol-3-yl)pyridine; C3H6O ¼ acetone), which occurs through ordered diffusion of acetone in a crystal-to-crystal manner, leading to dramatic structural changes. The slow kinetics of the transition allows thermal trapping of the system at various intermediate stages. The transiting single crystal can be then examined at these points through synchrotron SCXRD, offering a window upon the mechanism of the transformation at the molecular scale. These experiments have unveiled the development of an ordered intermediate phase, distinct from the initial and the final states, coexisting as the process advances with either of these two phases or, at a certain moment with both of them. The new intermediate phase has been structurally characterized in full detail by SCXRD, providing insights into the mechanism of this diffusion triggered solid-state phenomenon. The process has been also followed by calorimetry, optical microscopy, local Raman spectroscopy and powder X-ray diffraction. The discovery and description of an intermediate ordered state in a molecular solid-state transformation is of great interest and will help to understand the mechanistic details and reaction pathways underlying these transformations

Snapshots of a solid-state transformation: coexistence of three phases trapped in one crystal

Crystal-to-crystal transformations have been crucial in the understanding of solid-state processes, since these may be studied in detail by means of single crystal X-ray diffraction (SCXRD) techniques. The description of the mechanisms and potential intermediates of those processes remains very challenging. In fact, solid-state transient states have rarely been observed, at least to a sufficient level of detail. We have investigated the process of guest extrusion from the non-porous molecular material [Fe(bpp)(H2L)](ClO4)2$1.5C3H6O (bpp ¼ 2,6-bis(pyrazol-3-yl)pyridine; H2L ¼ 2,6-bis(5-(2- methoxyphenyl)-pyrazol-3-yl)pyridine; C3H6O ¼ acetone), which occurs through ordered diffusion of acetone in a crystal-to-crystal manner, leading to dramatic structural changes. The slow kinetics of the transition allows thermal trapping of the system at various intermediate stages. The transiting single crystal can be then examined at these points through synchrotron SCXRD, offering a window upon the mechanism of the transformation at the molecular scale. These experiments have unveiled the development of an ordered intermediate phase, distinct from the initial and the final states, coexisting as the process advances with either of these two phases or, at a certain moment with both of them. The new intermediate phase has been structurally characterized in full detail by SCXRD, providing insights into the mechanism of this diffusion triggered solid-state phenomenon. The process has been also followed by calorimetry, optical microscopy, local Raman spectroscopy and powder X-ray diffraction. The discovery and description of an intermediate ordered state in a molecular solid-state transformation is of great interest and will help to understand the mechanistic details and reaction pathways underlying these transformations