ABSTRACT
We report a synthesis of magnetic nanoparticles chemically immobilized onto reduced graphene oxide sheets (referred to as rGO-Fe3O4 NPs) as a gas and vapor sensing platform with precisely designed particle size of 5, 10 and 20â¯nm to explore their influence of particle size on sensing performance. The rGO-Fe3O4 NP sensors have been investigated their responses to different gases and volatile organic compounds (VOCs) at part-per-million (ppm) levels. Results show that the Fe3O4 NPs with smaller size (5 and 10â¯nm) on the rGO surface led to a lower sensitivity, while particles of a size of 20â¯nm have a significant enhancement of sensitivity compared to the bare rGO sensor. The rGO-Fe3O4 NP20 sensor can detect trace amounts of NO2 gas and ethanol vapor at the 1â¯ppm and is highly selective to the NO2 and ethanol among other tested gases and VOCs, respectively. The particle size causes different distribution behaviour of NPs over rGO surface and interspaced between them, which results in deceased or increased the surface interactions between gas and graphene. The NPs themselves contained different defects level and the charge depletion layer that affect their adsorption gas/vapor molecules, which are explained for different sensing responses.
ABSTRACT
Site-selective organic transformations are commonly required in the synthesis of complex molecules. By employing a bespoke metal-organic framework (MOF, 1·[Mn(CO)3N3]), in which coordinated azide anions are precisely positioned within 1D channels, we present a strategy for the site-selective transformation of dialkynes into alkyne-functionalized triazoles. As an illustration of this approach, 1,7-octadiyne-3,6-dione stoichiometrically furnishes the mono-"click" product N-methyl-4-hex-5'-ynl-1',4'-dione-1,2,3-triazole with only trace bis-triazole side-product. Stepwise insights into conversions of the MOF reaction vessel were obtained by X-ray crystallography, demonstrating that the reactive sites are "isolated" from one another. Single-crystal to single-crystal transformations of the Mn(I)-metalated material 1·[Mn(CO)3(H2O)]Br to the corresponding azide species 1·[Mn(CO)3N3] with sodium azide, followed by a series of [3+2] azide-alkyne cycloaddition reactions, are reported. The final liberation of the "click" products from the porous material is achieved by N-alkylation with MeBr, which regenerates starting MOF 1·[Mn(CO)3(H2O)]Br and releases the organic products, as characterized by NMR spectroscopy and mass spectrometry. Once the dialkyne length exceeds the azide separation, site selectivity is lost, confirming the critical importance of isolated azide moieties for this strategy. We postulate that carefully designed MOFs can act as physical protecting groups to facilitate other site-selective and chemoselective transformations.
ABSTRACT
The preparation of ruthenium complexes with novel 2,2'-bipyridine (bpy) ligands bearing four carboxylic acid groups was investigated with a view to creating dyes containing more than two potential anchoring groups per bpy unit for attachment to a titania surface. Synthetic challenges are encountered upon using the 2,2'-bipyridine-3,3',4,4'-tetracarboxylic acid ligand because it readily decarboxylates. The use of the methyl esterified derivative (3) proved to be more successful for complex preparation, with a robust preparation of the [Ru(3)2 Cl2 ] complex identified with diglyme as the solvent. This complex was further converted into the thiocyanato complex, [Ru(3)2 (NCS)2 ], which could not be completely de-esterified. X-ray analysis of crystals obtained from a mixture of isomers for this complex provided data for the S,S- and N,S-coordinated isomers; both showed a twisted arrangement of the pyridine rings in the 2,2'-bipyridine-3,3',4,4'-tetracarboxylic acid ligand, owing to steric hinderance. Conversely, the isosteric 2,2'-bipyridine-4,4',5,5'-tetracarboxylic acid ligand was easily converted into the desired [Ru(2)2 (NCS)2 ] complex through a standard one-pot procedure in N,N-dimethylformamide solvent. All of the complexes presented herein exhibit a significant redshift for the metal to ligand charge-transfer bands, relative to the benchmark ruthenium dye N719 and derivatives thereof. All complexes exhibit a quasi-reversible process for the ruthenium(II/III) couple at approximately 0.4â V versus the ferrocene couple, comparable to analogous ruthenium dyes.
ABSTRACT
Single-crystal X-ray crystallography is employed to characterize the reaction species of a full catalytic carbonylation cycle within a MnII -based metal-organic framework (MOF) material. The structural insights explain why the Rh metalated MOF is catalytically competent toward the carbonylation of MeBr but only affords stoichiometric turn-over in the case of MeI. This work highlights the capability of MOFs to act as platform materials for studying single-site catalysis in heterogeneous systems.
ABSTRACT
Post-synthetic modification of metal-organic frameworks (MOFs) facilitates a strategic transformation of potentially inert frameworks into functionalized materials, tailoring them for specific applications. In particular, the post-synthetic incorporation of transition-metal complexes within MOFs, a process known as 'metalation', is a particularly promising avenue towards functionalizing MOFs. Herein, we describe the post-synthetic metalation of a microporous MOF with various transition-metal nitrates. The parent framework, 1: , contains free-nitrogen donor chelation sites, which readily coordinate metal complexes in a single-crystal to single-crystal transformation which, remarkably, can be readily monitored by X-ray crystallography. The presence of an open void surrounding the chelation site in 1: prompted us to investigate the effect of the MOF pore environment on included metal complexes, particularly examining whether void space would induce changes in the coordination sphere of chelated complexes reminiscent of those found in the solution state. To test this hypothesis, we systematically metalated 1: with first-row transition-metal nitrates and elucidated the coordination environment of the respective transition-metal complexes using X-ray crystallography. Comparison of the coordination sphere parameters of coordinated transition-metal complexes in 1: against equivalent solid- and solution-state species suggests that the void space in 1: does not markedly influence the coordination sphere of chelated species but we show notably different post-synthetic metalation outcomes when different solvents are used.This article is part of the themed issue 'Coordination polymers and metal-organic frameworks: materials by design'.
ABSTRACT
The precise tuning of the structural and chemical features of microporous metal-organic frameworks (MOFs) is a crucial endeavour for developing materials with properties that are suitable for specific applications. In recent times, techniques for preparing frameworks consisting of mixed-metal or ligand compositions have emerged. However, controlled spatial organisation of the components within these structures at the molecular scale is a difficult challenge, particularly when species possessing similar geometries or chemical properties are used. Here, we describe the synthesis of mixed-metal and ligand variants possessing the Mn3L3 (Mn-MOF-1; H2L = bis(4-(4'-carboxyphenyl)-3,5-dimethylpyrazolyl)methane) structure type. In the case of mixed-ligand synthesis using a mixture of L and its trifluoromethyl-functionalised derivative (H2L' = bis(4-(4'-carboxyphenyl)-3,5-di(trifluoromethyl)pyrazolyl)methane), a mixed-ligand product in which the L' species predominanantly occupies the pillar sites lining the pores is obtained. Meanwhile, post-synthetic metal exchange of the parent Mn3L3 compound using Fe(2+) or Fe(3+) ions results in a degree of cation exchange at the trinuclear carboxylate-based clusters and metalation at the pillar bispyrazolate sites. The results demonstrate the versatility of the Mn3L3 structure type toward both metal and ligand substitutions, and the potential utility of site-specific functionalisations in achieving even greater precision in the tuning of MOFs.
ABSTRACT
Defect concentrations and their compensating groups have been systematically tuned within UiO-66 frameworks by using modified microwave-assisted solvothermal methods. Both of these factors have a pronounced effect on CO2 and H2O adsorption at low and high pressure.
ABSTRACT
Recent studies have demonstrated that metal-organic frameworks can be employed as protective coatings for enzymes. Two efficient strategies have been reported for the synthesis of such composite materials: biomimetic mineralisation and controlled co-precipitation using polyvinylpyrrolidone. We assessed the relative efficacy of each approach by comparing the thermal stability of encapsulated urease. The resulting data shows that over a range of temperatures biomimetic mineralisation offers superior protection than the co-precipitation method.
Subject(s)
Biomimetics , Capsules/chemistry , Chemical Precipitation , Imidazoles/chemistry , Organometallic Compounds/chemistry , Urease/chemistry , Zeolites/chemistry , Biomimetics/methods , Drug Stability , TemperatureABSTRACT
Porous metal-organic polyhedra (MOPs), constructed from heterometallic Pd(II)-M(II) (M = Cu, Ni, Zn) paddlewheel nodes and 5-tert-butyl-1,3-benzenedicarboxylate organic links, were prepared in which the Pd(II) ions preferentially line the inner surface of the cage molecules. Careful activation produces co-ordinatively unsaturated 3d transition metal sites on the external MOP surfaces giving rise to H2 adsorption enthalpies in excess of -12 kJ mol(-1).
ABSTRACT
Post-synthetic metallation is employed strategically to imbue metal-organic frameworks (MOFs) with enhanced performance characteristics. However, obtaining precise structural information for metal-centred reactions that take place within the pores of these materials has remained an elusive goal, because of issues with high symmetry in certain MOFs, lower initial crystallinity for some chemically robust MOFs, and the reduction in crystallinity that can result from carrying out post-synthetic reactions on parent crystals. Here, we report a new three-dimensional MOF possessing pore cavities that are lined with vacant di-pyrazole groups poised for post-synthetic metallation. These metallations occur quantitatively without appreciable loss of crystallinity, thereby enabling examination of the products by single-crystal X-ray diffraction. To illustrate the potential of this platform to garner fundamental insight into metal-catalysed reactions in porous solids we use single-crystal X-ray diffraction studies to structurally elucidate the reaction products of consecutive oxidative addition and methyl migration steps that occur within the pores of the Rh-metallated MOF, 1·[Rh(CO)2][Rh(CO)2Cl2].
ABSTRACT
This study describes the determination of the adsorption isotherms and binding kinetics of tagged recombinant proteins using a recently developed IMAC cassette system and employing automated robotic liquid handling procedures for IMAC resin screening. These results confirm that these new IMAC resins, generated from a variety of different metal-charged binuclear 1,4,7-triaza-cyclononane (tacn) ligands, interact with recombinant proteins containing a novel N-terminal metal binding tag, NT1A, with static binding capacities similar to those obtained with conventional hexa-His tagged proteins, but with significantly increased association constants. In addition, higher kinetic binding rates were observed with these new IMAC systems, an attribute that can be positively exploited to increase process productivity. The results from this investigation demonstrate that enhancements in binding capacities and affinities were achieved with these new IMAC resins and chosen NT1A tagged protein. Further, differences in the binding performances of the bis(tacn) xylenyl-bridged ligands were consistent with the distance between the metal binding centres of the two tacn moieties, the flexibility of the ligand and the potential contribution from the aromatic ring of the xylenyl group to undergo π/π stacking interactions with the tagged proteins.
Subject(s)
Aza Compounds/chemistry , Chromatography, Affinity/instrumentation , Metals/chemistry , Piperidines/chemistry , Recombinant Proteins/chemistry , Adsorption , Automation , Indicators and Reagents , Kinetics , Ligands , Protein BindingABSTRACT
The effect of pore functionalisation (-I, -OH, -OCH3) on a series of topologically equivalent, interpenetrated metal-organic frameworks (MOFs) was assessed by both simulation and experiment. Counter-intuitively, a decreased affinity for CO2 was observed in the functionalised materials, compared to the non-functionalised material. This result highlights the importance of considering the combined effects of network topology and chemical functionality in the design of MOFs for enhanced CO2 adsorption.