RESUMO
The majority of reported metallo-supramolecules are highly symmetric homoleptic assemblies of M x L y type, with a few reports on assemblies that are obtained using multicomponent self-assembly or using ambidentate ligands. Herein, we report the use of an unsymmetrical tetratopic ligand (Lun) containing pyridyl and imidazole donor sites in combination with a cis-protected Pd(ii) acceptor for the formation of a low-symmetry M8Lun 4 molecular barrel (UNMB). Four potential orientational isomeric (HHHH, HHHT, HHTT, and HTHT) molecular barrels can be anticipated for the M8Lun 4 type metallo-assemblies. However, the formation of an orientational isomer (HHTT) of the barrel was suggested from single-crystal X-ray diffraction and 1H NMR analysis of UNMB. Two large open apertures at terminals and the hydrophobic confined space surrounded by four aromatic panels of Lun make UNMB a potential host for bigger guests. UNMB encapsulates fullerenes C70 and C60 favoured by non-covalent interactions between the fullerenes and aromatic panels of the ligand molecules. Experimental and theoretical studies revealed that UNMB has the ability to bind C70 more strongly than its lower analogue C60. The stronger affinity of UNMB towards C70 was exploited to separate C70 from an equimolar mixture of C70 and C60. Moreover, C70 can be extracted from the C70âUNMB complex by toluene, and therefore, UNMB can be reused as a recyclable separating agent for C70 extraction.
RESUMO
Three nuclear weapons tests were conducted in the 1950s at the Montebello Islands, Western Australia. The detonations were of different yields and configurations (two tower tests, one ship test), and led to substantial radionuclide contamination within the surrounding terrestrial and marine ecosystems. The region possesses great ecological and recreational significance, particularly within the marine environment. However, studies conducted so far have largely neglected the marine ecosystem which makes up the majority of the Montebello Island Marine Park and in which most test fallout would have deposited. Here we investigated the distribution of the transuranic radionuclides 238Pu, 239,240Pu and 241Am in marine sediment from the Montebello Islands. Marine sediment samples near Operation Mosaic G2 and Operation Hurricane were collected and analysed by gamma and alpha spectrometry. Activity concentrations of 239,240Pu across both series ranged from 45 to 2900 Bq kg-1, while 241Am levels ranged from 2.8 to 70 Bq kg-1. Higher activity concentrations were observed in sediment near the land-based, higher yield Mosaic G2 test, compared with the ship-based, lower yield Hurricane test. Sediment samples located closer to the detonation site were also observed to have higher activity concentrations. Radioactive particles of 0.94 mm and 1.5 mm in diameter were identified by analysis of size-fractioned sediment via investigation of 152Eu levels, photostimulated autoradiography and point gamma spectroscopy. Particles were confirmed to have transuranic radionuclide interiors, with surface coatings which were dominated by vitrified CaCO3. Their long-term resistance to weathering and subsequent persistence in the marine environment can therefore be attributed to their coated structural form. Our study confirms the persistence of transuranic radionuclides in Montebello Island marine sediment and highlights the need for additional studies to improve our understanding of the nuclear legacy in this region.
Assuntos
Sedimentos Geológicos , Plutônio , Monitoramento de Radiação , Poluentes Radioativos da Água , Sedimentos Geológicos/química , Sedimentos Geológicos/análise , Austrália Ocidental , Plutônio/análise , Poluentes Radioativos da Água/análise , Amerício/análise , Ilhas , Armas NuclearesRESUMO
The structural dynamics involved in the mechanical flexibility of molecular crystals and the internal stress in such flexible materials remain obscure. Here, the study reports an elastically bending lipidated molecular crystal that shows systematic shifts in characteristic vibrational frequencies across the bent crystal region - revealing the nature of structural changes during bending and the local internal stress distribution. The blueshifts in the bond stretching modes (such as CâO and C-H modes) in the inner arc region and redshifts in the outer arc region of the bent crystals observed via micro-Raman mapping are counterintuitive to the bending models based on intermolecular hydrogen bonds. Correlating these shifts with the trends observed from high-pressure Raman studies on the crystal reveals the local stress difference between the inner arc and outer arc regions of the bent crystal to be ≈2 GPa, more than an order of magnitude higher than the previously proposed value in elastically bending crystals. High local internal stress can have direct ramifications on the properties of molecular piezoelectric energy harvesters, actuators, semiconductors, and flexible optoelectronic materials.
RESUMO
In order to bind guest molecules with exquisite selectivity, biological host molecules often employ low symmetry binding pockets. The majority of metallosupramolecular assemblies, however, rely on symmetrical ligands to form high-symmetry assemblies that enclosing similarly symmetrical cavities. Here we employ an unsymmetrical quaterpyridine ligand in combination with cobalt(II) to form a mixture of low-symmetry [M2L3] helicates and [M4L6] tetrahedra and their subsequent oxidation to Co(III)-containing assemblies.
RESUMO
In biological systems, enzymes and transport proteins can bind anions in aqueous media solely by forming hydrogen bonds with charge-neutral motifs. Reproducing this functionality in synthetic systems presents challenges and incurs high costs, particularly when targeting strongly hydrated anions such as sulfate. Here we report a [2.2.2]urea cryptand (cage), synthesized in one pot, that selectively binds sulfate in a mixture of dimethyl sulfoxide and water and in water with affinities in the micromolar to millimolar range. The neutral cage bearing six urea groups donates 12 strong hydrogen bonds to encapsulate a sulfate anion, showing favourable enthalpy even in pure water. Sulfate binding can be further enhanced by using micelles to provide a low-polarity microenvironment. The cage finds utility in analysing divalent anions in water and beverage samples or in removing sulfate. The work demonstrates the achievability of robust and selective anion binding in water with minimal synthetic efforts, by using neutral NH hydrogen bonds akin to those found in biology.
RESUMO
Embracing complexity in design, metallo-supramolecular self-assembly presents an opportunity for fabricating materials of economic significance. The array of accessible supramolecules is alluring, along with favourable energy requirements. Implementation is hampered by an inability to efficiently characterise complex mixtures. The stoichiometry, size, shape, guest binding properties and reactivity of individual components and combinations thereof are inherently challenging to resolve. A large combinatorial library of four transition metals (Fe, Cu, Ni and Zn), and six ß-diketonate ligands at different molar ratios and pH was robotically prepared and directly analysed over multiple timepoints with electrospray ionisation travelling wave ion mobility-mass spectrometry. The dataset was parsed for self-assembling activity without first attempting to structurally assign individual species. Self-assembling systems were readily categorised without manual data-handling, allowing efficient screening of self-assembly activity. This workflow clarifies solution phase supramolecular assembly processes without manual, bottom-up processing. The complex behaviour of the self-assembling systems was reduced to simpler qualities, which could be automatically processed.
RESUMO
Through coordination-driven self-assembly, aesthetically captivating structures can be formed by tuning the length or flexibility of various components. The self-assembly of an elongated rigid terphenyl-based tetra-pyridyl ligand (L1) with a cis-Pd(II) acceptor produces an [M12 L16 ]24+ triangular orthobicupola structure (1). When flexibility is introduced into the ligand by the incorporation of a -CH2 - group between the dipyridylamine and terphenyl rings in the ligand (L2), anunique [M8 L24 ]16+ water-soluble 'intertwined cubic structure' (2) results. The inherent flexibility of ligand L2 might be the key factor behind the formation of the thermodynamically stable and 'intertwined cubic structure' in this scenario. This research showcases the ability to design and fabricate novel, topologically distinctive molecular structures by a straightforward and efficient approach.
RESUMO
Spin crossover (SCO) complexes can reversibly switch between low spin (LS) and high spin (HS) states, affording possible applications in sensing, displays, and molecular electronics. Dinuclear SCO complexes with access to [LS-LS], [LS-HS], and [HS-HS] states may offer increased levels of functionality. The nature of the SCO interconversion in dinuclear complexes is influenced by the local electronic environment. We report the synthesis and characterization of [{FeIII(tpa)}2spiro](PF6)2 (1), [{FeIII(tpa)}2Br4spiro](PF6)2 (2), and [{FeIII(tpa)}2thea](PF6)2 (3) (tpa = tris(2-pyridylmethyl)amine, spiroH4 = 3,3,3',3'-tetramethyl-1,1'-spirobi(indan)-5,5',6,6'-tetraol, Br4spiroH4 = 3,3,3',3'-tetramethyl-1,1'-spirobi(indan)-4,4',7,7'-tetrabromo-5,5',6,6'-tetraol, theaH4 = 2,3,6,7-tetrahydroxy-9,10-dimethyl-9,10-dihydro-9,10-ethanoanthracene), utilizing non-conjugated bis(catecholate) bridging ligands. In the solid state, magnetic and structural analysis shows that 1 remains in the [HS-HS] state, while 2 and 3 undergo a partial SCO interconversion upon cooling from room temperature involving the mixed [LS-HS] state. In solution, all complexes undergo SCO from [HS-HS] at room temperature, via [LS-HS] to mixtures including [LS-LS] at 77 K, with the extent of SCO increasing in the order 1 < 2 < 3. Gas phase density functional theory calculations suggest a [LS-LS] ground state for all complexes, with the [LS-HS] and [HS-HS] states successively destabilized. The relative energy separations indicate that ligand field strength increases following spiro4- < Br4spiro4- < thea4-, consistent with solid-state magnetic and EPR behavior. All three complexes show stabilization of the [LS-HS] state in relation to the midpoint energy between [LS-LS] and [HS-HS]. The relative stability of the [LS-HS] state increases with increasing ligand field strength of the bis(catecholate) bridging ligand in the order 1 < 2 < 3. The bromo substituents of Br4spiro4- increase the ligand field strength relative to spiro4-, while the stronger ligand field provided by thea4- arises from extension of the overlapping π-orbital system across the two catecholate units. This study highlights how SCO behavior in dinuclear complexes can be modulated by the bridging ligand, providing useful insights for the design of molecules that can be interconverted between more than two states.
RESUMO
Despite the use of achiral ligands, the vast majority of metallosupramolecular assemblies containing octahedral tris-bidentate metal centres show strong stereochemical communication between metal centres, generally resulting in homochiral assemblies even though they are statistically disfavoured. Here we show that when resolved stereocentres are attached to the central part of a quaterpyridine ligand, the stereochemical coupling from this centre is insufficient to disrupt the strong stereochemical communication between metal centres in both [M2L3] helicates and [M4L6] tetrahedra.
RESUMO
Artificial molecular machines have captured the full attention of the scientific community since Jean-Pierre Sauvage, Fraser Stoddart, and Ben Feringa were awarded the 2016 Nobel Prize in Chemistry. The past and current developments in molecular machinery (rotaxanes, rotors, and switches) primarily rely on organic-based compounds as molecular building blocks for their assembly and future development. In contrast, the main group chemical space has not been traditionally part of the molecular machine domain. The oxidation states and valency ranges within the p-block provide a tremendous wealth of structures with various chemical properties. Such chemical diversityâwhen implemented in molecular machinesâcould become a transformative force in the field. Within this context, we have rationally designed a series of NH-bridged acyclic dimeric cyclodiphosphazane species, [(µ-NH){PE(µ-NtBu)2PE(NHtBu)}2] (E = O and S), bis-PV2N2, displaying bimodal bifurcated R21(8) and trifurcated R31(8,8) hydrogen bonding motifs. The reported species reversibly switch their topological arrangement in the presence and absence of anions. Our results underscore these species as versatile building blocks for molecular machines and switches, as well as supramolecular chemistry and crystal engineering based on cyclophosphazane frameworks.
RESUMO
Coordination cages can be used for enantio- and regioselective catalysis and for the selective sensing and separation of isomeric guest molecules. Here, stereoisomers of a family of coordination cages are resolved using ultra-high-resolution cyclic ion-mobility mass spectrometry (cIM-MS). The observed ratio of diastereomers is dependent on both the metal ion and counter ion. Moreover, the point groups can be assigned through complementary NMR experiments. This method enables the identification and interrogation of the individual isomers in complex mixtures of cages which cannot be performed in solution. Furthermore, these techniques allow the stability of individual isomers within the mixture to be probed, with the T-symmetric isomers in this case shown to be more robust than the C3 and S4 analogues.
RESUMO
Two isomorphous fluorescent (FL) lantern-shaped metal-organic cages 1 and 2 were prepared by coordination-directed self-assembly of Co(II) centers with a new aza-crown macrocyclic ligand bearing pyridine pendant arms (Lpy). The cage structures were determined using single-crystal X-ray diffraction analysis, thermogravimetric, elemental microanalysis, FT-IR spectroscopy, and powder X-ray diffraction. The crystal structures of 1 and 2 show that anions (Cl- in 1 and Br- in 2) are encapsulated within the cage cavity. 1 and 2 bear two coordinated water molecules that are directed inside the cages, surrounded by the eight pyridine rings at the "bottom" and the "roof" of the cage. These hydrogen bond donors, π systems, and the cationic nature of the cages enable 1 and 2 to encapsulate the anions. FL experiments revealed that 1 could detect nitroaromatic compounds by exhibiting selective and sensitive fluorescence quenching toward p-nitroaniline (PNA), recommending a limit of detection of 4.24 ppm. Moreover, the addition of 50 µL of PNA and o-nitrophenol to the ethanolic suspension of 1 led to a significant large FL red shift, namely, 87 and 24 nm, respectively, which were significantly higher than the corresponding values observed in the presence of other nitroaromatic compounds. The titration of the ethanolic suspension of 1, with various concentrations of PNA (>12 µM) demonstrated a concentration-dependent emission red shift. Hence, the efficient FL quenching of 1 was capable of distinguishing the dinitrobenzene isomers. Meanwhile, the observed red shift (10 nm) and quenching of this emission band under the influence of a trace amount of o- and p-nitrophenol isomers also showed that 1 could discriminate between o- and p-nitrophenol. Replacement of the chlorido with a bromido ligand in 1 generated cage 2 which was a more electron-donating cage than 1. The FL experiments showed that 2 was partially more sensitive and less selective toward NACs than 1.
RESUMO
CX-ASAP is a new open-source software project designed to greatly reduce the time required to analyse crystallographic data collected under varying conditions. Scripted in Python3, CX-ASAP can automatically refine, finalize and analyse data collections with wide-ranging temperatures, pressures etc. This is achieved using a reference structure, allowing for quick identification of problems, phase changes and even model comparison. The modular design means that new features and customized scripts can be easily added, tailoring the capabilities to the specific needs of the user. It is envisioned that CX-ASAP will help to close the growing gap between fast collection times and slow data finalization.
RESUMO
Molecular crystals displaying elastic flexibility have important applications in the fields of optoelectronics and nanophotonic technologies. Understanding the mechanisms by which these materials bend is critical to the design of future materials incorporating these properties. Based on the known elastic properties of bis(acetylacetonato)copper(II), a series of 14 aliphatic derivatives are synthesized and crystallized. All those which grew in a needle morphology display noticeable elasticity, with 1D chains of π-stacked molecules parallel to the long metric length of the crystal a consistent crystallographic feature. Crystallographic mapping is used to measure the mechanism of elasticity at an atomic-scale. Symmetric derivatives with ethyl and propyl side chains are found to have different mechanisms of elasticity, which are further distinguished from the previously reported mechanism of bis(acetylacetonato)copper(II). While crystals of bis(acetylacetonato)copper(II) are known to bend elastically via a molecular rotation mechanism, the elasticity of the compounds presented is facilitated by expansion of their π-stacking interactions.
RESUMO
Organic materials are promising candidates for the development of efficient sensors for many medicinal and materials science applications. Single crystals of a small molecule, 4-trifluoromethyl phenyl isothiocyanate (4CFNCS), exhibit plastic deformation when bent, twisted, or coiled. Synchrotron micro-focus X-ray diffraction mapping of the bent region of the crystal confirms the mechanism of deformation. The crystals are incorporated into a flexible piezoresistive sensor using a composite constituting PEDOT: PSS/4CFNCS, which shows an impressive performance at high-pressure ranges (sensitivity 0.08 kPa-1 above 44 kPa).
RESUMO
Polycyclic aromatic hydrocarbons (PAHs) find multiple applications ranging from fabric dyes to optoelectronic materials. Hydrogenation of PAHs is often employed for their purification or derivatization. However, separation of PAHs from their hydrogenated analogues is challenging because of their similar physical properties. An example of such is the separation of 9,10-dihydroanthracene from phenanthrene/anthracene which requires fractional distillation at high temperature (â¼340 °C) to obtain pure anthracene/phenanthrene in coal industry. Herein we demonstrate a new approach for this separation at room temperature using a water-soluble interlocked cage (1) as extracting agent by host-guest chemistry. The cage was obtained by self-assembly of a triimidazole donor L·HNO3 with cis-[(tmeda)Pd(NO3)2] (M) [tmeda = N,N,N',N'-tetramethylethane-1,2-diamine]. 1 has a triply interlocked structure with an inner cavity capable of selectively binding planar aromatic guests.
RESUMO
The interplay of many factors influences the outcomes of self-assembly reactions. Using an acetylene-appended quaterpyridine ligand we show that both the size of the metal ion and the presence of steric repulsion between the acetylene groups result in the exclusive formation of [M2L3] helicates rather than a helicate/tetrahedron equilibrium.
RESUMO
A detailed study of the two-dimensional (2-D) Hofmann-like framework [Fe(furpy)2Pd(CN)4]·nG (furpy: N-(pyridin-4-yl)furan-2-carboxamide, G = H2O,EtOH (A·H2O,Et), and H2O (A·H2O)) is presented, including the structural and spin-crossover (SCO) implications of subtle guest modification. This 2-D framework is characterized by undulating Hofmann layers and an array of interlayer spacing environmentsâthis is a strategic approach that we achieve by the inclusion of a ligand with multiple host-host and host-guest interaction sites. Variable-temperature magnetic susceptibility studies reveal an asymmetric multistep SCO for A·H2O,Et and an abrupt single-step SCO for A·H2O with an upshift in transition temperature of â¼75 K. Single-crystal analyses show a primitive orthorhombic symmetry for A·H2O,Et characterized by a unique FeII centerâthe multistep SCO character is attributed to local ligand orientation. Counterintuitively, A·H2O shows a triclinic symmetry with two inequivalent FeII centers that undergo a cooperative single-step high-spin (HS)-to-low-spin (LS) transition. We conduct detailed structure-function analyses to understand how the guest ethanol influences the delicate balance between framework communication and, therefore, the local structure and spin-state transition mechanism.
RESUMO
Inclusion of an angular bridging ligand, 4,2':6',4''-terpyridine (TPy), into a Hofmann-type framework produces an irregular network in which six- and five-coordinate FeII species co-exist. The octahedral sites show thermally-induced spin-crossover (SCO) and the rare five-coordinate FeII sites are high-spin.
RESUMO
Anthracene crude oil is a common source of phenanthrene for its industrial use. The isolation of phenanthrene from this source is a challenging task due to very similar physical properties to its isomer anthracene. We report here a water-soluble Pd(II) molecular boat (MB1) with unusual structural topology that was obtained by assembling a flexible tetrapyridyl donor (L) with a cis-Pd(II) acceptor. The flexible backbone of the boat enabled it to breathe in the presence of a guest optimizing the fit within the cavity. The boat binds phenanthrene more strongly than anthracene, which enabled separation of phenanthrene with an >98% purity from an equimolar mixture of the two isomers using MB1 as an extracting agent. MB1 represents a unique example of a coordination receptor suitable for selective aqueous extraction of phenanthrene from anthracene with reusability of several cycles.