The novel porous {M(F‐pymo)2}n⋅2.5n H2O coordination networks (M=Co, Zn; F‐pymo=5‐fluoropyrimidin‐2‐olate), possessing sodalitic topology, have been synthesised and structurally characterised by ...means of powder diffraction methods. Thermodiffractometry demonstrated their plasticity: when heated up to 363 K, they reversibly transform into three‐dimensional dehydrated {M(F‐pymo)2}n species, with significantly different lattice parameters. Further heating induces irreversible polymorphic transformations into layered phases, in which the original MN4 coordination sphere changes into an MN3O one. A mixed‐metal phase, {CoxZn1−x(F‐pymo)2}n⋅2.5n H2O, was also prepared, showing that zinc is preferentially inserted, when starting from a Co/Zn reagent ratio of 1:1. The solid–gas adsorption properties of the anhydrous 3D frameworks have been explored towards N2, H2 (77 K) and CH4, CO2 (273 K). These results show that these materials permit the diffusion of CO2 molecules only. Remarkably, the CO2 adsorption process for the {Co(F‐pymo)2}n network proceeds in two steps: the first step takes place at low pressures (<600 kPa) and the second one above a threshold pressure of 600 kPa. By contrast, the {Zn(F‐pymo)2}n network only permits CO2 diffusion by applying pressures above 900 kPa. This type of behaviour is typical of porous networks with gated channels. The high CO2 selectivity of these systems over the rest of the essayed probe gases is explained in terms of flexibility and polarity of the porous network. Finally, the magnetic studies on the CoII systems reveal that the as synthesised {Co(F‐pymo)2}n⋅2.5n H2O material behaves as an antiferromagnet with a TN of about 29 K. At variance, the {Co(F‐pymo)2}n layered phase shows an unusually weak ferromagnetic ordering below 17 K, arising from a spin‐canting phenomenon.
Flexible MOFs! Application of high‐pressure CO2 or exposure to moisture of a zeomimetic coordination network induces a reversible structural change from a non‐porous β‐phase to a porous α‐phase (see figure). An additional structural transformation into a layered γ‐phase is promoted by thermal treatment implying a concomitant modification of the physicochemical properties.
A novel approach toward the obtaining of a Pd (II) carbon-supported catalyst based on a statistical distributed polymer (hyperbranched polyethyleneimine) and its use as a highly efficient and ...sustainable catalyst for Sonogashira-type coupling reactions is presented. The heterogenous Pd (II)/HBPEI catalyst fabricated through a facile, cost-effective and scalable procedure provides an innovative catalyst structure based on statistical distributed singular catalytic centers with well-defined Pd-Polymer chemical interactions, highly resistant to suffer leaching processes and extensively and homogenously distributed across the whole carbon surface. The catalyst exhibited excellent catalytic and recycling activity for several cross-coupling reactions between different aryl halides and terminal alkynes, free of any undesired by-product and in excellent yields, under air atmosphere, using water as solvent, at moderate temperatures (65 °C) and avoiding the use of phosphine derivatives, Cu(I) as co-catalyst and excess of any of the reactant. Therefore, the reported Pd(II)-HBPEI carbon-supported material can be considered a truly competitive heterogeneous Pd(II) catalyst for large-scale under green chemistry conditions.
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•Hyperbranched polyethyleneimine Pd(II)-complexing properties•Heterogeneous polymer-based Sonogashira catalyst for large-scale applications•Pd (II) catalyst based on porous carbon supports•Phosphine-, and sulfur-free heterogeneous palladium catalyst•Cross-coupling reaction under mild, aerobic, green and co-catalyst free conditions
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•H2 plasma removes oxygen groups but not the sulfonyl and sulfonic groups.•Water treatment + H2 plasma treatment removes 60% of oxygen and 100% of sulfur.•This methodology removes as ...much oxygen as NaBH4 but is simpler, faster and cleaner.•The oxygen remaining after H2 plasma reduction forms labile surface groups.•Three GOs were tested rendering similar results.
We report the reduction of GO by hydrogen cold plasma as an effective alternative to the usual chemical (with harsh reducing agents) or physical (through high-temperature treatments) methods. The hydrogen plasma is generated through microwave radiation and the reduction is performed barely above room temperature, avoiding structural degradation of the graphene oxide. Three commercial GOs, with several oxygen and sulfur contents, have been used in this study. As a consequence of the exposure to the hydrogen plasma, the oxygen content is decreased in large extent while sulfur is scarcely removed. Thus a two-stage methodology consisting of a simple water treatment under reflux conditions of GO (to remove sulfur) and further treatment with H2 plasma is proposed. The combination of both steps allows the total elimination of sulfur while achieving very high degrees of reduction, lowering the initial oxygen content by more than 60%. These degrees of reduction are comparable to those obtained when the reduction is carried out by using the standard procedure with NaBH4 on the same materials. The reduction with hydrogen plasma clearly shows advantages over the conventional reduction procedures due to its simplicity: no chemicals or high temperatures are needed, and the procedure is very fast.
A stable, extensive amine functionalization was introduced on the surface of an activated carbon (AC) through very effective grafting of a polyethyleneimine layer onto the AC surface. The procedures ...used are simple, sustainable and easily scalable. Among the large variety of possible applications that the polyamine functionality confers to the AC, its outstanding properties as Pd(II) adsorbent are here presented.
Photo-induced darkening of red cinnabar (HgS) has attracted the interest of many researchers as it drastically impacts the visual perception of artworks. Darkening has commonly been related to ...metallic mercury (Hg
) formation in the presence of chlorides. Based on the study of UV-aged cinnabar pigment and tempera paint we propose an alternative pathway for the blackening reaction of cinnabar, considering its semiconductor properties and pigment-binder interactions. We demonstrate that darkening is caused by the oxidation of cinnabar to mercury sulfates and subsequent reduction to Hg
via photo-induced electron transfer without the involvement of chlorides, and provide direct evidence for the presence of Hg
on UV-aged tempera paint. Photooxidation also affects the organic binder, causing a competing depletion of photo-generated holes and consequently limiting but not impeding mercury sulfate formation and subsequent reduction to Hg
. In addition, organics provide active sites for Hg
sorption, which is ultimately responsible for the darkening of cinnabar-based paint.
Due to the fast, emerging development of antibiotic-resistant bacteria, the need for novel, efficient routes to battle these pathogens is crucial; in this scenario, metal-organic frameworks (MOFs) ...are promising materials for combating them effectively. Herein, a novel Cu-MOF-namely
-that displays the formula Cu
L
(DMF)
(DMF =
,
-dimethylformamide) is described, synthesized by the combination of copper(II) and 3,4-dihydroxybenzoic acid (H
L)-both having well-known antibacterial properties. The resulting three-dimensional structure motivated us to study the antibacterial activity, adsorptive capacity and processability of the MOF in the form of pellets and membranes as a proof-of-concept to evaluate its future application in devices.
The novel coordination polymers Cu(Hoxonic)(H2O)n (1) and Cu(Hoxonic)(bpy)0.5n⋅1.5 n H2O (2⊂H2O) (H3oxonic: 4,6‐dihydroxy‐1,3,5‐triazine‐2‐carboxylic acid; bpy: 4,4′‐bipyridine) have been isolated ...and structurally characterised by ab initio X‐ray powder diffraction. The dense phase 1 contains 1D zig‐zag chains in which Hoxonic dianions bridge square‐pyramidal copper(II) ions, apically coordinated by water molecules. On the contrary, 2⊂H2O, prepared by solution and solventless methods, is based on 2D layers of octahedral copper(II) ions bridged by Hoxonic ligands, further pillared by bpy spacers. The resulting pro‐porous 3D network possesses small hydrated cavities. The reactivity, thermal, magnetic and adsorptive properties of these materials have been investigated. Notably, the adsorption studies on 2 show that this material possesses unusual adsorption behaviour. Indeed, guest uptake is facilitated by increasing the thermal energy of both the guest and the framework. Thus, neither N2 at 77 K nor CO2 at 195 K are incorporated, and CH4 is only minimally adsorbed at 273 K and high pressures (0.5 mmol g−1 at 2500 kPa). By contrast, CO2 is readily incorporated at 273 K (up to 2.5 mmol g−1 at 2500 kPa). The selectivity of 2 towards CO2 over CH4 has been investigated by means of variable‐temperature zero coverage adsorption experiments and measurement of breakthrough curves of CO2/CH4 mixtures. The results show the highly selective incorporation of CO2 in 2, which can be rationalised on the basis of the framework flexibility and polar nature of its voids.
Flexible MOFs: The unusual adsorption behaviour and guest selectivity of a pro‐porous flexible copper(II) coordination network have been rationalised on the basis of thermal XRPD and variable‐temperature adsorption experiments of probe gases (N2, CH4, CO2) of environmental interest (see figure).