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1.
Chempluschem ; 85(5): 845-854, 2020 May.
Artigo em Inglês | MEDLINE | ID: mdl-32378813

RESUMO

In this Minireview we outline the development of cyclic aliphatic moieties as ligands in metal-organic frameworks (MOFs), with a focus on the relationship between ligand design and synthesis and the properties of the subsequent materials. Aliphatic ligands have received considerably less attention than aromatic analogues in MOF chemistry but offer advantages in their unique combinations of geometric and electronic properties which are unattainable from conventional ligands. Here, we focus on rigid and semi-rigid backbone moieties derived from monocyclic and fused polycyclic aliphatic backbones, including cyclohexane and adamantane, cubane and bicyclo[2.2.2]octane, and discuss the synthetic chemistry of these species along with their potential importance as the next generation of building blocks for microporous materials.

2.
Sci Adv ; 5(11): eaax9171, 2019 11.
Artigo em Inglês | MEDLINE | ID: mdl-31819904

RESUMO

CO2 accumulation in confined spaces represents an increasing environmental and health problem. Trace CO2 capture remains an unmet challenge because human health risks can occur at 1000 parts per million (ppm), a level that challenges current generations of chemisorbents (high energy footprint and slow kinetics) and physisorbents (poor selectivity for CO2, especially versus water vapor, and/or poor hydrolytic stability). Here, dynamic breakthrough gas experiments conducted upon the ultramicroporous material SIFSIX-18-Ni-ß reveal trace (1000 to 10,000 ppm) CO2 removal from humid air. We attribute the performance of SIFSIX-18-Ni-ß to two factors that are usually mutually exclusive: a new type of strong CO2 binding site and hydrophobicity similar to ZIF-8. SIFSIX-18-Ni-ß also offers fast sorption kinetics to enable selective capture of CO2 over both N2 (S CN) and H2O (S CW), making it prototypal for a previously unknown class of physisorbents that exhibit effective trace CO2 capture under both dry and humid conditions.

3.
Chem Commun (Camb) ; 55(88): 13271-13274, 2019 Oct 31.
Artigo em Inglês | MEDLINE | ID: mdl-31621761

RESUMO

Dinuclear [M2L2]n+ (M = Pd2+ or Pt2+) metallo-rectangles have a rich history, particularly in molecular recognition, including self-catenation events. These structures are mostly generated via a ligand-directed approach with cis-capped M2+ corners. We report here a symmetry interaction approach using 3 : 1 complementary denticity, giving a new route to [M2L2]4+ rectangles and their self-catenation.

4.
Chem Asian J ; 14(19): 3404-3408, 2019 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-31483940

RESUMO

The use of stimuli to induce reversible structural transformations in metallosupramolecular systems is of keen interest to chemists seeking to mimic the way that Nature effects conformational changes in biological machinery. While a wide array of stimuli have been deployed towards this end, stoichiometric changes have only been explored in a handful of examples. Furthermore, switching has generally been between only two distinct states. Here we use a simple 2-(1-(pyridine-4-methyl)-1H-1,2,3-triazol-4-yl)pyridine "click" ligand in combination with PdII in various stoichiometries and concentrations to quantitatively access and cycle between three distinct species: a [PdL2 ]2+ monomer, a [Pd2 L2 ]4+ dimer, and a [Pd9 L12 ]18+ cage.

5.
Chem Commun (Camb) ; 55(69): 10304-10307, 2019 Aug 22.
Artigo em Inglês | MEDLINE | ID: mdl-31397447

RESUMO

Herein, the synthesis of metal-organic tetrahedral cages featuring flexible thio- and selenophosphate-based ligands is described. The cages were prepared by sub-component self-assembly of A[double bond, length as m-dash]P(OC6H4NH2-4)3 (A = S, Se) or S[double bond, length as m-dash]P(SC6H4NH2-4)3, 2-pyridinecarboxaldehyde, and either Fe[BF4]2 or Co[BF4]2. Preliminary host-guest studies into the ability of the pendant P[double bond, length as m-dash]S and P[double bond, length as m-dash]Se groups to interact with suitable substrates will be discussed.

6.
ACS Nano ; 13(7): 8087-8098, 2019 Jul 23.
Artigo em Inglês | MEDLINE | ID: mdl-31244037

RESUMO

Atomically dispersed metal catalysts anchored on nitrogen-doped (N-doped) carbons demand attention due to their superior catalytic activity relative to that of metal nanoparticle catalysts in energy storage and conversion processes. Herein, we introduce a simple and versatile strategy for the synthesis of hollow N-doped carbon capsules that contain one or more atomically dispersed metals (denoted as H-M-Nx-C and H-Mmix-Nx-C, respectively, where M = Fe, Co, or Ni). This method utilizes the pyrolysis of nanostructured core-shell precursors produced by coating a zeolitic imidazolate framework core with a metal-tannic acid (M-TA) coordination polymer shell (containing up to three different metal cations). Pyrolysis of these core-shell precursors affords hollow N-doped carbon capsules containing monometal sites (e.g., Fe-Nx, CoNx, or Ni-Nx) or multimetal sites (Fe/Co-Nx, Fe/Ni-Nx, Co/Ni-Nx, or Fe/Co/Ni-Nx). This inventory allowed exploration of the relationship between catalyst composition and electrochemical activity for the oxygen reduction reaction (ORR) in acidic solution. H-Fe-Nx-C, H-Co-Nx-C, H-FeCo-Nx-C, H-FeNi-Nx-C, and H-FeCoNi-Nx-C were particularly efficient ORR catalysts in acidic solution. Furthermore, the H-Fe-Nx-C catalyst exhibited outstanding initial performance when applied as a cathode material in a proton exchange membrane fuel cell. The synthetic methodology introduced here thus provides a convenient route for developing next-generation catalysts based on earth-abundant components.

7.
Chem Asian J ; 14(13): 2225-2229, 2019 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-31090192

RESUMO

The synthesis and physico-chemical characterization of an FeII complex [Fe(L1)3 ](ClO4 )2 ⋅CH3 CN⋅0.5H2 O, 1, incorporating a bidentate imidazolylimine-based ligand are reported. Complex 1 crystallises as the mer-isomer and the crystal lattice is replete with hydrogen bonding interactions between ClO4 - anions, solvent molecules and imidazole N-H groups. Variable-temperature structural, magnetic, photomagnetic and optical reflectivity techniques have been deployed to fully characterise the spin-crossover (SCO) behaviour in 1 along with its desolvated phase, 1⋅desolv. Variable-temperature (1.8-300 K) magnetic-susceptibility measurements reveal a broad two-step full SCO for 1 (T1/2 =158 and 184 K) and photomagnetic experiments at 10 K under white-light irradiation revealed complete photo-induced SCO. 1⋅desolv displays considerably different magnetic behaviour with sharp single-step SCO accompanied by a thermal hysteresis (T1/2↑ =105 K, T1/2↓ =95 K) in addition to full photo-induced SCO at lower temperatures.

8.
Chemistry ; 25(7): 1781-1786, 2019 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-30481392

RESUMO

Structural changes to metallosupramolecular assemblies resulting in the release or uptake of guests are currently well established, whereas transformations turning on and off specific self-recognition are far less developed. We report a novel ligand (2,6-bis(1-(3-pyridin-4-yl)phenyl-1H-1,2,3-triazol-4-yl)pyridine) possessing a tridentate central metal-binding site flanked by two pendant pyridyl arms. In a 2:1 ratio with PdII metal ions, a spiro-type [PdL2 ]2+ "Figure-of-eight" complex forms with the central tridentate binding pocket unoccupied. The introduction of an additional one equivalent of PdII metal ion results in the conversion to a dimeric [Pd2 L2 ]4+ molecule with the tridentate pocket occupied. There is site-specific self-recognition between dimers in solution with strong NOE peaks between adjacent molecules. The self-recognition between dimers can be turned off in two ways: firstly, adding another equivalent of PdII metal ion brings about binding to the previously uncoordinated pyridyl arms that are key to the self-recognition event, and; secondly, addition of sufficient ligand to return the stoichiometry to 2:1 regenerates the [PdL2 ]2+ complex. Hence, the self-recognition event can be turned on or off through simple variation of L:PdII stoichiometry.

9.
Chem Commun (Camb) ; 54(95): 13391-13394, 2018 Nov 27.
Artigo em Inglês | MEDLINE | ID: mdl-30421754

RESUMO

The dinuclear mesocate [Fe2L3](BF4)4, 1, is a supramolecular building block for a microporous material. Structural analysis reveals that extensive noncovalent interactions in the solid state generate a 3D framework with microporous channels. These channels are permanently accessible to incoming guest molecules and adsorption isotherms demonstrate that the material has a high selectivity for CO2 over N2.

10.
Dalton Trans ; 47(24): 7965-7974, 2018 Jun 19.
Artigo em Inglês | MEDLINE | ID: mdl-29862409

RESUMO

Dinuclear triple-helicate complexes of the formula [Fe2L3](BF4)4·solv (solv = CH3CN, CHCl3, H2O) have been synthesised and structurally characterised. The bis-bidentate ligands, L, present either strong-field 2-pyridylimine (1) or weaker-field 2-imidazolylimine (2) and 4-imidazolylimine (3) coordination spheres about Fe(ii) centres in an octahedral geometry. Whereas 1 is pervasively diamagnetic, spin crossover (SCO) behaviour is observed in 2 and 3 and has been studied using variable-temperature structural, UV-visible spectroscopic, magnetic and photo-magnetic techniques. Variable-temperature (1.8-400 K) magnetic-susceptibility measurements reveal the T1/2 values of 2 and 3 to be strongly dependent upon the solvent and degree of solvation. Photomagnetic studies at 10 K under white-light irradiation revealed an inefficient photo-induced SCO in 2, but full switching in 3.

11.
ACS Nano ; 12(5): 4594-4604, 2018 05 22.
Artigo em Inglês | MEDLINE | ID: mdl-29667838

RESUMO

Nanoparticles comprising three or more different metals are challenging to prepare. General methods that tackle this challenge are highly sought after as multicomponent metal nanoparticles display favorable properties in applications such as catalysis, biomedicine, and imaging. Herein, we report a practical and versatile approach for the synthesis of nanoparticles composed of up to four different metals. This method relies on the thermal decomposition of nanostructured composite materials assembled from platinum nanoparticles, a metal-organic framework (ZIF-8), and a tannic acid coordination polymer. The controlled integration of multiple metal cations (Ni, Co, Cu, Mn, Fe, and/or Tb) into the tannic acid shell of the precursor material dictates the composition of the final multicomponent metal nanoparticles. Upon thermolysis, the platinum nanoparticles seed the growth of the multicomponent metal nanoparticles via coalescence with the metallic constituents of the tannic acid coordination polymer. The nanoparticles are supported in the walls of hollow nitrogen-doped porous carbon capsules created by the decomposition of the organic components of the precursor. The capsules prevent sintering and detachment of the nanoparticles, and their porosity allows for efficient mass transport. To demonstrate the utility of producing a broad library of supported multicomponent metal nanoparticles, we tested their electrocatalytic performance toward the hydrogen evolution reaction and oxygen evolution reaction. We discovered functional relationships between the composition of the nanoparticles and their electrochemical activity and identified the PtNiCu and PtNiCuFe nanoparticles as particularly efficient catalysts. This highlights how to generate diverse libraries of multicomponent metal nanoparticles that can be synthesized and subsequently screened to identify high-performance materials for target applications.

12.
Dalton Trans ; 47(3): 783-790, 2018 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-29243746

RESUMO

We have investigated the hydrogen bond-driven assembly of nickel and freebase tetra(carboxyphenyl) and tetra(carboxylatophenyl) porphyrins. When the tetracarboxylates were crystallized with bis(amidinium) species, their crystal structures contained a range of hydrogen bond geometries, and we did not obtain well-ordered networks. Use of a tetrahedral tetra(amidinium) building block yielded a 3D framework material with a PtS topology, which contains only a "paired" hydrogen bonding arrangement. This framework is highly porous, with ∼3/4 of the unit cell volume occupied by disordered solvent molecules, although it loses crystallinity upon removal from solvent. Favourable interactions between porphyrin carboxylic acid hydrogen bond donors and bipyridine nitrogen atoms were then used to prepare a stable 2D porphyrin grid-like network.

13.
Inorg Chem ; 56(20): 12224-12231, 2017 Oct 16.
Artigo em Inglês | MEDLINE | ID: mdl-28945078

RESUMO

An isoreticular family of seven microporous metal-organic frameworks of the general form [ZnL] have been synthesized, where L is a 4'-substituted 2,2':6',2″-terpyridine-4,4″-dicarboxylate ligand. Each framework adopts an interpenetrated zeolitic gismondine (gis-c) topology and possesses one-dimensional square channels with ca. 9.0 Šapertures running down the crystallographic c axis. Gas adsorption measurements with N2, H2, CH4, and CO2 confirm their permanent porosity. The ligand functional groups, which include phenyl, 2-tolyl, 4-chlorophenyl, 4-nitrophenyl, 2-thienyl, 3-thienyl, and 4-pyridyl, line the channel walls and tune the gas adsorption properties of these materials.

14.
Chem Asian J ; 12(13): 1649-1658, 2017 Jul 04.
Artigo em Inglês | MEDLINE | ID: mdl-28503856

RESUMO

Electrochemiluminescence (ECL) based on [Ru(bpy)3 ]2+ systems is widely utilized for immunoassays. In order to extend the promising potential of ECL-based applications, IrIII complexes have recently attracted attention as probes because of their excellent luminescent properties and tunable emission wavelength. Here we describe a series of Ir complexes using a large π-conjugated ligand and different ancillary chelates. The complexes synthesized have been chemically and spectroscopically characterized and used for ECL measurements with annihilation and co-reactant methods. One of the IrIII complexes investigated exhibits the brightest, ever reported, ECL efficiency in acetonitrile employing the benzoyl peroxide (BPO) co-reactant method.

15.
Chemistry ; 23(29): 7052-7065, 2017 May 23.
Artigo em Inglês | MEDLINE | ID: mdl-28474778

RESUMO

A family of halogen-substituted Schiff base iron(II) complexes, [FeII (qsal-X)2 ], (qsal-X=5-X-N-(8-quinolyl)salicylaldimines)) in which X=F (1), Cl (2), Br (3) or I (4) has been investigated in detail. Compound 1 shows a temperature invariant high spin state, whereas the others all show abrupt spin transitions, at or above room temperature, namely, 295 K (X=I) up to 342 K (X=Br), these being some of the highest T1/2 values obtained, to date, for FeII N/O species. We have recently reported subtle symmetry breaking in [FeII (qsal-Cl)2 ] 2 with two spin transition steps occurring at 308 and 316 K. A photomagnetic study reveals almost full HS conversion of [FeII (qsal-I)2 ] 4 at low temperature (T(LIESST)=54 °K). The halogen substitution effects on the magnetic properties, as well as the crystal packing of the [FeII (qsal-X)2 ] compounds and theoretical calculations, are discussed in depth, giving important knowledge for the design of new spin crossover materials. In comparison to the well known iron(III) analogues, [FeIII (qsal-X)2 ]+ , the two extra π-π and P4AE interactions found in [FeII (qsal-X)2 ] compounds, are believed to be accountable for the spin transitions occurring at ambient temperatures.

16.
Chem Commun (Camb) ; 53(8): 1374-1377, 2017 Jan 24.
Artigo em Inglês | MEDLINE | ID: mdl-28074968

RESUMO

[Fe(qsal-Cl)2] is one of the few known Fe(ii) spin crossover compounds with an N4O2 donor atom environment. It shows an abrupt two-step spin transition at 308 and 316 K and importantly, symmetry breaking at the highest temperature reported, to date, in spin crossover compounds.

17.
J Am Chem Soc ; 138(36): 11872-81, 2016 09 14.
Artigo em Inglês | MEDLINE | ID: mdl-27575666

RESUMO

We report a new methodology for producing monometallic or bimetallic nanoparticles confined within hollow nitrogen-doped porous carbon capsules. The capsules are derived from metal-organic framework (MOF) crystals that are coated with a shell of a secondary material comprising either a metal-tannic acid coordination polymer or a resorcinol-formaldehyde polymer. Platinum nanoparticles are optionally sandwiched between the MOF core and the shell. Pyrolysis of the MOF-shell composites produces hollow capsules of porous nitrogen-doped carbon that bear either monometallic (Pt, Co, and Ni) or alloyed (PtCo and PtNi) metal nanoparticles. The Co and Ni components of the bimetallic nanoparticles are derived from the shell surrounding the MOF crystals. The hollow capsules prevent sintering and detachment of the nanoparticles, and their porous walls allow for efficient mass transport. Alloyed PtCo nanoparticles embedded in the capsule walls are highly active, selective, and recyclable catalysts for the hydrogenation of nitroarenes to anilines.

18.
Inorg Chem ; 54(19): 9483-90, 2015 Oct 05.
Artigo em Inglês | MEDLINE | ID: mdl-26365676

RESUMO

We report a strategy that employs metal-organic framework (MOF) crystals in two roles for the fabrication of hollow nanomaterials. In the first role the MOF crystals provide a template on which a shell of material can be deposited. Etching of the MOF produces a hollow structure with a predetermined size and morphology. In combination with this strategy, the MOF crystals, including guest molecules in their pores, can provide the components of a secondary material that is deposited inside the initially formed shell. We used this approach to develop a straightforward and reproducible method for constructing well-defined, nonspherical hollow and exceptionally porous titania and titania-based composite nanomaterials. Uniform hollow nanostructures of amorphous titania, which assume the cubic or polyhedral shape of the original template, are delivered using nano- and microsized ZIF-8 and ZIF-67 crystal templates. These materials exhibit outstanding textural properties including hierarchical pore structures and BET surface areas of up to 800 m(2)/g. As a proof of principle, we further demonstrate that metal nanoparticles such as Pt nanoparticles, can be encapsulated into the TiO2 shell during the digestion process and used for subsequent heterogeneous catalysis. In addition, we show that the core components of the ZIF nanocrystals, along with their adsorbed guests, can be used as precursors for the formation of secondary materials, following their thermal decomposition, to produce hollow and porous metal sulfide/titania or metal oxide/titania composite nanostructures.

19.
Inorg Chem ; 54(16): 7735-41, 2015 Aug 17.
Artigo em Inglês | MEDLINE | ID: mdl-26222397

RESUMO

The tripodal terpyridine ligand, L, forms 1D helical supramolecular polymers/gels in H2O-CH3OH solution mediated through hydrogen bonding and π-π interactions. These gels further cross-link into 3D supramolecular metallogels with a range of metal ions (M) such as Fe(II), Ni(II), Cu(II), Zn(II), and Ru(III); the cross-linking resulting in the formation of colored or colorless gels. The fibrous morphology of these gels was confirmed using scanning electron microscopy (SEM); while the self-assembly processes between L and M were investigated by absorbance and emission spectroscopy from which their binding constants were determined by using a nonlinear regression analysis.


Assuntos
Metais Pesados/química , Piridinas/química , Géis , Ligantes
20.
Dalton Trans ; 44(19): 9269-80, 2015 May 21.
Artigo em Inglês | MEDLINE | ID: mdl-25913411

RESUMO

The synthesis, structural and thermal characterisation of a number of coordination complexes featuring the N,O-heteroditopic ligand 4-(3,5-dimethyl-1H-pyrazol-4-yl)benzoate, HL are reported. The reaction of H2L with cobalt(II) and nickel(II) nitrates at room temperature in basic DMF/H2O solution gave discrete mononuclear coordination complexes with the general formula {[M(HL)2(H2O)4]·2DMF} (M = Co (1), Ni (2)), whereas the reaction with zinc(II) nitrate gave [Zn(HL)2]∞, 3, a coordination polymer with distorted diamondoid topology and fourfold interpenetration. Coordination about the tetrahedral Zn(II) nodes in 3 are furnished by two pyrazolyl nitrogen atoms and two carboxylate oxygen atoms to give a mixed N2O2 donor set. Isotopological coordination polymers of zinc(II), {[Zn(HL)2]·2CH3OH·H2O}∞, 4, and cobalt(II), [Co(HL)2]∞, 5, are formed when the reactions are carried out under solvothermal conditions in methanol (80 °C) and water (180 °C), respectively. The reaction of H2L with cadmium(II) nitrate at room temperature in methanol gives {[Cd(HL)2(MeOH)2]·1.8MeOH}∞6, a 2-D (4,4)-connected coordination polymer, whereas with copper(II) the formation of green crystals that transform into purple crystals is observed. The metastable green phase [Cu3(HL)4(µ2-SO4)(H2O)3]∞, 7, crystallises with conserved binding domains of the heteroditopic ligand and contains two different metal nodes: a dicopper carboxylate paddle wheel motif, and, a dicopper unit bridged by sulfate ions and coordinated by ligand pyrazolyl nitrogen atoms. The resultant purple phase {[Cu(HL)2]·4CH3OH·H2O}∞, 8, however, has single copper ion nodes coordinated by mixed N2O2 donor sets with trans-square planar geometry and is threefold interpenetrated. The desolvation of 8 was followed by powder X-ray diffraction and single crystal X-ray diffraction which show desolvation induces the transition to a more closely packed structure while the coordination geometry about the copper ions and the network topology is retained. Powder X-ray diffraction and microanalysis were used to characterise the bulk purity of the coordination materials 1­6 and 8. The thermal characteristics of 1­2, 4­6 and 8 were studied by TG-DTA. This led to the curious observation of small exothermic events in networks 4, 6, and 8 that appear to be linked to their decomposition. In addition, the solid state structures of H2L and that of its protonated salt, H2L·HNO3, were also determined and revealed that H2L forms a 2-D hydrogen bonded polymer incorporating helical chains formed through N­HO and O­HN interactions, and that [H3L]NO3 forms a 1-D hydrogen-bonded polymer.

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