Influence of the Surface Chemistry of Metal-Organic Polyhedra in Their Assembly into Ultrathin Films for Gas Separation

The formation of ultrathin films of Rh-based porous metal-organic polyhedra (Rh-MOPs) by the Langmuir-Blodgett method has been explored. Homogeneous and dense monolayer films were formed at the air-water interface either using two different coordinatively alkyl-functionalized Rh-MOPs (HRhMOP(diz)12 and HRhMOP(oiz)12) or by in situ incorporation of aliphatic chains to the axial sites of dirhodium paddlewheels of another Rh-MOP (OHRhMOP) at the air-liquid interface. All these Rh-MOP monolayers were successively deposited onto different substrates in order to obtain multilayer films with controllable thicknesses. Aliphatic chains were partially removed from HRhMOP(diz)12 films post-synthetically by a simple acid treatment, resulting in a relevant modification of the film hydrophobicity. Moreover, the CO2/N2 separation performance of Rh-MOP-supported membranes was also evaluated, proving that they can be used as selective layers for efficient CO2 separation. © 2022 The Authors. Published by American Chemical Society

Influence of the surface chemistry of metal-organic polyhedra in their assembly into ultrathin films for gas separation

The formation of ultrathin films of Rh-based porous metal–organic polyhedra (Rh-MOPs) by the Langmuir–Blodgett method has been explored. Homogeneous and dense monolayer films were formed at the air–water interface either using two different coordinatively alkyl-functionalized Rh-MOPs (HRhMOP(diz)12 and HRhMOP(oiz)12) or by in situ incorporation of aliphatic chains to the axial sites of dirhodium paddlewheels of another Rh-MOP (OHRhMOP) at the air–liquid interface. All these Rh-MOP monolayers were successively deposited onto different substrates in order to obtain multilayer films with controllable thicknesses. Aliphatic chains were partially removed from HRhMOP(diz)12 films post-synthetically by a simple acid treatment, resulting in a relevant modification of the film hydrophobicity. Moreover, the CO2/N2 separation performance of Rh-MOP-supported membranes was also evaluated, proving that they can be used as selective layers for efficient CO2 separation.This work was funded by MCIN/AEI/10.13039/501100011033 and ERDF “A way of making Europe” (grant PID2019-105881RB-I00). The authors also acknowledge the support from the Spanish MINECO (project RTI2018-095622-B-I00) and the Catalan AGAUR (project 2017 SGR 238). It was also funded by the CERCA Programme/Generalitat de Catalunya and through a fellowship (LCF/BQ/PR20/11770011) from “la Caixa” Foundation (ID 100010434). ICN2 is supported by the Severo Ochoa programme from the Spanish MINECO (grant no. SEV-2017-0706). I.T. and M.P.-M. gratefully acknowledge their DGA PhD fellowship from Government of Aragon. The microscopy work was carried out in the Laboratorio de Microscopias Avanzadas at the Instituto de Nanociencia y Materiales de Aragon (LMA-INMA). This work benefited from the use of the SasView application, originally developed under NSF award DMR-0520547. SasView contains code developed with funding from the European Union’s Horizon 2020 research and innovation programme under the SINE2020 project, grant agreement no. 654000. The authors thank the synchrotron SOLEIL for beamtime provision under projects 20190435 and 20191874.Peer reviewe

Supporting information for the manuscript Influence of the Surface Chemistry of Metal–Organic Polyhedra in Their Assembly into Ultrathin Films for Gas Separation

19 pages. -- Figure S1. Absorption spectra (450-650 nm range) of OHRhMOP dissolved in methanol/chloroform (1:5) and the product formed after the addition of ca. 3.8×10- 3 mmol of diz to a dispersion of ca. 1.5×10-4 mmol OHRhMOP in 2 mL of THF. The maximum absorption at ca. 552 nm after diz addition indicates that all the dirhodium paddlewheels of OHRhMOP are coordinated to one diz, obtaining OHRhMOP(diz)12. -- Figure S2. Raw GIXD data for C12RhMOP (left), HRhMOP(diz)12 (middle) and OHRhMOP (right), at the indicated pressures. The water subphase data are shown as grey lines. Insets highlight the q range exhibiting the Bragg peak of alkyl chains ordering, in the case of C12RhMOP and HRhMOP(diz)12. -- Figure S3. Top: high q portion of GIXD data for C12RhMOP (left, collapsed) and HRhMOP(diz)12 (right, 10 mN/m), integrated over only the bottom half, top half, bottom first quarter or the whole detector, as indicated. The Bragg peak at ca. 1.51 Å-1 characteristic of alkyl chain interdigitation/order is not present in the data at higher qz. Bottom: intensity of the alkyl chains Bragg rod vs. qz, C12RhMOP. -- Figure S4. GIXD data for OHRhMOP at the gas-water interface at 10 mN/m, after correction for the water subphase. The red line is the diffusion form factor of coreshell spheres with an empty (SLD = 0) core of 5 Å radius and a dense shell of 11.5 Å thickness (SLD = 2x10-6 Å-2), considering a pinhole instrumental smearing dQ/Q of 5 %, that can only account for the two stronger peaks at 0.63 and 0.87 Å–1. (left), HRhMOP(diz)12 (right) at 10 mN/m. -- Scheme S1. LS sequential deposition of MOP monolayers onto PTMSP supports. One MOP monolayer is deposited each time that the support contacts the film formed at the air-liquid interface. After each transfer, the film is dried with N2 at ambient temperature and the transference is repeated as many times as necessary to obtain films with the desired number of Rh-MOP monolayers. -- Figure S5. UV-Vis spectra for the three Rh-MOPs studied. Solution spectra and LS films deposited onto quartz substrates are compared for each Rh-MOP. -- Figure S6. Representative AFM topography images from HRhMOP(oiz)12 and HRhMOP(diz)12 LS films transferred onto quartz substrates at 20 mN/m used to evaluate the film thickness. -- Figure S7. Representative AFM topography image of quartz, left, and a Si(100), right, substrates before MOP film deposition. -- Figure S8. Representative AFM topography and phase images from a OHRhMOP LS film transferred at 2 mN/m and evaluation of film thickness and defects dimensions. -- Figure S9. Linear increase of the absorbance at 214 nm vs. the number of Rh- MOP LS layers transferred at 20 mN/m onto quartz substrates (● HRhMOP(oiz)12;■: HRhMOP(diz)12). -- Figure S10. Rh-MOP mass deposited onto QCM disks at 20 mN/m versus the number of LS layers transferred (■: C12RhMOP;▲: HRhMOP(oiz)12, ●: HRhMOP(diz)12). -- Figure S11. Brewster Angle Microscope (BAM) images obtained during OHRhMOP + diz film compression at indicated surface pressures and the corresponding areas per molecule. OHRhMOP + diz different ratios were used in the experiments (1:25 in top images, and 1:50 in bottom images, respectively). -- Figure S12. Characterization of the films obtained from OHRhMOP + diz (1:25) reaction at the air-liquid interface: a) UV-Vis spectra from sequential deposition of LS films transferred onto quartz at 20 mN/m. Inset: Linear increase of the absorbance at 221nm vs. the number of LS layers transferred. b) Mass deposited onto QCM disks vs. the number of LS layers transferred (red line: OHRhMOP +diz; blue line: HRhMOP(diz)12, green line: C12RhMOP). -- Figure S13: UV-Vis spectra from HRhMOP(diz)12 LS films deposited onto quartz at 20 mN/m before and after the acid treatment: 1 layer (continuous line) and 3 layers (dashed line). -- Figure S14. Representative AFM topography and phase images from a HRhMOP(diz)12 LS film (1 layer) deposited onto Si (100) before and after acid treatment with HCl vapors. -- Table S1: Parameters of the components used to simulate the Rh 3d high resolution XPS spectra (see Figure 9) of OHRhMOP (powder), 1 LS film deposited at 20 mN/m after OHRhMOP + diz (1:25) reaction at the air-liquid interface and drop-cast film obtained after OHRhMOP + diz (1:25) reaction in THF. -- Table S2: Comparison of the performance of MOP and PIM ultrathin films (30 LS monolayers deposited onto PTMSP membranes) in CO2/N2 (10/90 in volume) separation at 35 ºC. At least 2 different samples were fabricated and measured to provide the corresponding error estimations.The formation of ultrathin films of Rh-based porous metal–organic polyhedra (Rh-MOPs) by the Langmuir–Blodgett method has been explored. Homogeneous and dense monolayer films were formed at the air–water interface either using two different coordinatively alkyl-functionalized Rh-MOPs (HRhMOP­(diz)12 and HRhMOP­(oiz)12) or by in situ incorporation of aliphatic chains to the axial sites of dirhodium paddlewheels of another Rh-MOP (OHRhMOP) at the air–liquid interface. All these Rh-MOP monolayers were successively deposited onto different substrates in order to obtain multilayer films with controllable thicknesses. Aliphatic chains were partially removed from HRhMOP­(diz)12 films post-synthetically by a simple acid treatment, resulting in a relevant modification of the film hydrophobicity. Moreover, the CO2/N2 separation performance of Rh-MOP-supported membranes was also evaluated, proving that they can be used as selective layers for efficient CO2 separation.Peer reviewe

Spatiotemporal control of supramolecular polymerization and gelation of metal-organic polyhedra

In coordination-based supramolecular materials such as metallogels, simultaneous temporal and spatial control of their assembly remains challenging. Here, we demonstrate that the combination of light with acids as stimuli allows for the spatiotemporal control over the architectures, mechanical properties, and shape of porous soft materials based on metal–organic polyhedra (MOPs). First, we show that the formation of a colloidal gel network from a preformed kinetically trapped MOP solution can be triggered upon addition of trifluoroacetic acid (TFA) and that acid concentration determines the reaction kinetics. As determined by time-resolved dynamic light scattering, UV–vis absorption, and 1H NMR spectroscopies and rheology measurements, the consequences of the increase in acid concentration are (i) an increase in the cross-linking between MOPs; (ii) a growth in the size of the colloidal particles forming the gel network; (iii) an increase in the density of the colloidal network; and (iv) a decrease in the ductility and stiffness of the resulting gel. We then demonstrate that irradiation of a dispersed photoacid generator, pyranine, allows the spatiotemporal control of the gel formation by locally triggering the self-assembly process. Using this methodology, we show that the gel can be patterned into a desired shape. Such precise positioning of the assembled structures, combined with the stable and permanent porosity of MOPs, could allow their integration into devices for applications such as sensing, separation, catalysis, or drug release

Evolution of form in metal-organic frameworks

Self-assembly has proven to be a widely successful synthetic strategy for functional materials, especially for metal-organic materials (MOMs), an emerging class of porous materials consisting of metal-organic frameworks (MOFs) and metal-organic polyhedra (MOPs). However, there are areas in MOM synthesis in which such self-assembly has not been fully utilized, such as controlling the interior of MOM crystals. Here we demonstrate sequential self-assembly strategy for synthesizing various forms of MOM crystals, including double-shell hollow MOMs, based on single-crystal to single-crystal transformation from MOP to MOF. Moreover, this synthetic strategy also yields other forms, such as solid, core-shell, double and triple matryoshka, and single-shell hollow MOMs, thereby exhibiting form evolution in MOMs. We anticipate that this synthetic approach might open up a new direction for the development of diverse forms in MOMs, with highly advanced areas such as sequential drug delivery/release and heterogeneous cascade catalysis targeted in the foreseeable future.ope

Ultrathin films of porous metal–organic polyhedra for gas separation

Ultrathin films of a robust RhII‐based porous metal–organic polyhedra (MOP) have been obtained. Homogeneous and compact monolayer films (ca. 2.5 nm thick) were first formed at the air–water interface, deposited onto different substrates and characterized using spectroscopic methods, scanning transmission electron microscopy and atomic force microscopy. As a proof of concept, the gas separation performance of MOP‐supported membranes has also been evaluated. Selective MOP ultrathin films (thickness ca. 60 nm) exhibit remarkable CO2 permeance and CO2/N2 selectivity, demonstrating the great combined potential of MOP and Langmuir‐based techniques in separation technologies.This work was supported by the Spanish MINECO (projects RTI2018‐095622‐B‐I00, MAT2016‐78257‐R, MAT2016‐77290‐R and MAT2017‐86826‐R), the Catalan AGAUR (project 2017 SGR 328), the ERC under the EU‐FP7 (ERC‐Co 615954), the CERCA Program/Generalitat de Catalunya and the Aragon Government (T43_17R and E31_17R research groups). ICN2 is supported by the Severo Ochoa program from Spanish MINECO (SEV‐2017‐0706). A.C.‐S. thanks the Spanish MINECO for Juan de la Cierva fellowship (IJCI‐2016‐29802), J. S.‐L. and M.A.A thank the Spanish Education Ministry Program FPU2014 for their Ph.D. grants.Peer reviewe

A Coordinative Solubilizer Method to Fabricate Soft Porous Materials from Insoluble Metal-Organic Polyhedra

Porous molecular cages have a characteristic processability arising from their solubility, which allows their incorporation into porous materials. Attaining solubility often requires covalently bound functional groups that are unnecessary for porosity and which ultimately occupy free volume in the materials, decreasing their surface areas. Here, a method is described that takes advantage of the coordination bonds in metal–organic polyhedra (MOPs) to render insoluble MOPs soluble by reversibly attaching an alkyl‐functionalized ligand. We then use the newly soluble MOPs as monomers for supramolecular polymerization reactions, obtaining permanently porous, amorphous polymers with the shape of colloids and gels, which display increased gas uptake in comparison with materials made with covalently functionalized MOPs

Photoactive carbon monoxide-releasing coordination polymer particles

We report the synthesis of photoactive carbon monoxide-releasing coordination polymer particles through the assembly of Mn(i) carbonyl complexes with bis(imidazole) ligands. The use of Mn(i) carbonyl complexes as metallic nodes in the coordination network avoids the potential for aggregation-induced self-quenching, favouring their use in the solid state

Phase transfer of rhodium(II)-based metal-organic polyhedra bearing coordinatively bound cargo enables molecular separation

The transfer of nanoparticles between immiscible phases can be driven by externally triggered changes in their surface composition. Interestingly, phase transfers can enhance the processing of nanoparticles and enable their use as vehicles for transporting molecular cargo. Herein we report extension of such phase transfers to encompass porous metal-organic polyhedra (MOPs). We report that a hydroxyl-functionalized, cuboctahedral Rh(II)-based MOP can be transferred between immiscible phases by pH changes or by cation-exchange reactions. We demonstrate use of this MOP to transport coordinatively bound cargo between immiscible layers, including into solvents in which the cargo is insoluble. As proof-of-concept that our phase-transfer approach could be used in chemical separation, we employed Rh(II)-based MOPs to separate a challenging mixture of structurally similar cyclic aliphatic (tetrahydrothiophene) and aromatic (thiophene) compounds. We anticipate that transport of coordinatively bound molecules will open new avenues for molecular separation based on the relative coordination affinity that the molecules have for the Rh(II) sites of MOP.Thais Grancha, Arnau Carné-Sánchez, Laura Hernández-López, Jorge Albalad, Inhar Imaz, Judith Juanhuix, and Daniel Maspoc