Showing papers by "J. Fraser Stoddart published in 2014"
TL;DR: A new Hf-based metal-organic framework (Hf-NU-1000) incorporating Hf6 clusters is reported, demonstrating high catalytic efficiency for the activation of epoxides and facilitating the quantitative chemical fixation of CO2 into five-membered cyclic carbonates under ambient conditions, rendering this material an excellent catalyst.
Abstract: Porous heterogeneous catalysts play a pivotal role in the chemical industry. Herein a new Hf-based metal–organic framework (Hf-NU-1000) incorporating Hf6 clusters is reported. It demonstrates high catalytic efficiency for the activation of epoxides, facilitating the quantitative chemical fixation of CO2 into five-membered cyclic carbonates under ambient conditions, rendering this material an excellent catalyst. As a multifunctional catalyst, Hf-NU-1000 is also efficient for other epoxide activations, leading to the regioselective and enantioretentive formation of 1,2-bifuctionalized systems via solvolytic nucleophilic ring opening.
437 citations
TL;DR: The routes to chemically modified pillar[n]arenes are described by discussing the chemistry of their functionalization: monofunctionalization, difunctionalized, rim differentiation, perfunctionalization, and phenylene substitution and the synthetic complications of employing these functionalization procedures are assessed.
Abstract: ConspectusMacrocyclic chemistry has relied on the dominance of some key cavitands, including cyclodextrins, calixarenes, cyclophanes, and cucurbiturils, to advance the field of host–guest science. Very few of the many other cavitands introduced by chemists during these past few decades have been developed to near the extent of these four key players. A relatively new family of macrocycles that are becoming increasingly dominant in the field of macrocyclic chemistry are the pillar[n]arenes composed of n hydroquinone rings connected in their 2- and 5-positions by methylene bridges. This substitution pattern creates a cylindrical or pillar-like structure that has identical upper and lower rims. The preparation of pillar[n]arenes is facile, with pillar[5]- through pillar[7]arene being readily accessible and the larger macrocycles (n = 8–14) being accessible in diminishing yields. The rigid pillar[n]arene cavities are highly π-electron-rich on account of the n activated aromatic faces pointing toward their cen...
419 citations
TL;DR: It is emphasized how rotaxanes constitute a remarkably versatile platform for directing force and motion, owing to the wide range of stimuli that can be used to actuate them and their diverse modes of mechanical switching as dictated by the stereochemistry of their mechanical bonds.
Abstract: ConspectusMore than two decades of investigating the chemistry of bistable mechanically interlocked molecules (MIMs), such as rotaxanes and catenanes, has led to the advent of numerous molecular switches that express controlled translational or circumrotational movement on the nanoscale. Directed motion at this scale is an essential feature of many biomolecular assemblies known as molecular machines, which carry out essential life-sustaining functions of the cell. It follows that the use of bistable MIMs as artificial molecular machines (AMMs) has been long anticipated. This objective is rarely achieved, however, because of challenges associated with coupling the directed motions of mechanical switches with other systems on which they can perform work.A natural source of inspiration for designing AMMs is muscle tissue, since it is a material that relies on the hierarchical organization of molecular machines (myosin) and filaments (actin) to produce the force and motion that underpin locomotion, circulatio...
413 citations
TL;DR: The free primary hydroxyl groups in the metal-organic framework of CDMOF-2, an extended cubic structure containing units of six γ-cyclodextrin tori linked together in cube-like fashion by rubidium ions, has been shown to react with gaseous CO2 to form alkyl carbonate functions.
Abstract: The free primary hydroxyl groups in the metal–organic framework of CDMOF-2, an extended cubic structure containing units of six γ-cyclodextrin tori linked together in cube-like fashion by rubidium ions, has been shown to react with gaseous CO2 to form alkyl carbonate functions. The dynamic covalent carbon–oxygen bond, associated with this chemisorption process, releases CO2 at low activation energies. As a result of this dynamic covalent chemistry going on inside a metal–organic framework, CO2 can be detected selectively in the atmosphere by electrochemical impedance spectroscopy. The “as-synthesized” CDMOF-2 which exhibits high proton conductivity in pore-filling methanolic media, displays a ∼550-fold decrease in its ionic conductivity on binding CO2. This fundamental property has been exploited to create a sensor capable of measuring CO2 concentrations quantitatively even in the presence of ambient oxygen.
211 citations
TL;DR: This report illustrates the principles of enzyme catalysis (first proposed by Pauling and Jencks) through a well-defined model system that has been fully characterized crystallographically, computationally and kinetically.
Abstract: Stereoelectronic complementarity between the active site of an enzyme and the transition state of a reaction is one of the tenets of enzyme catalysis. This report illustrates the principles of enzyme catalysis (first proposed by Pauling and Jencks) through a well-defined model system that has been fully characterized crystallographically, computationally and kinetically. Catalysis of the bowl-to-bowl inversion processes that pertain to corannulene is achieved by combining ground-state destabilization and transition-state stabilization within the cavity of an extended tetracationic cyclophane. This synthetic receptor fulfils a role reminiscent of a catalytic antibody by stabilizing the planar transition state for the bowl-to-bowl inversion of (ethyl)corannulene (which accelerates this process by a factor of ten at room temperature) by an induced-fit mechanism first formulated by Koshland.
122 citations
TL;DR: Two azobenzene α-cyclodextrin based nanovalves are designed, synthesized and assembled on mesoporous silica nanoparticles and demonstrated to be reversible and capable of multiuse.
Abstract: Two azobenzene α-cyclodextrin based nanovalves are designed, synthesized and assembled on mesoporous silica nanoparticles. Under aqueous conditions, the cyclodextrin cap is tightly bound to the azobenzene moiety and capable of holding back loaded cargo molecules. Upon irradiation with a near-UV light laser, trans to cis-photoisomerization of azobenzene initiates a dethreading process, which causes the cyclodextrin cap to unbind followed by the release of cargo. The addition of a bulky stopper to the end of the stalk allows this design to be reversible; complete dethreading of cyclodextrin as a result of unbinding with azobenzene is prevented as a consequence of steric interference. As a result, thermal relaxation of cis- to trans-azobenzene allows for the rebinding of cyclodextrin and resealing of the nanopores, a process which entraps the remaining cargo. Two stalks were designed with different lengths and tested with alizarin red S and propidium iodide. No cargo release was observed prior to light irradiation, and the system was capable of multiuse. On/off control was also demonstrated by monitoring the release of cargo when the light stimulus was applied and removed, respectively.
120 citations
TL;DR: In this paper, an enantiomeric pair of doubly-bridged naphthalene-1,8:4,5-bis(dicarboximide) cyclophanes and the characterization of four of their electronic states, namely 1) the ground state, 2) the exciton coupled singlet excited state, 3) the radical anion with strong through-space interactions between the redox-active NDI molecules, and 4) the diamagnetic diradical dianion using UV/Vis/NIR, EPR and END
Abstract: Investigating through-space electronic communication between discrete cofacially oriented aromatic π-systems is fundamental to understanding assemblies as diverse as double-stranded DNA, organic photovoltaics and thin-film transistors. A detailed understanding of the electronic interactions involved rests on making the appropriate molecular compounds with rigid covalent scaffolds and π-π distances in the range of ca. 3.5 A. Reported herein is an enantiomeric pair of doubly-bridged naphthalene-1,8:4,5-bis(dicarboximide) (NDI) cyclophanes and the characterization of four of their electronic states, namely 1) the ground state, 2) the exciton coupled singlet excited state, 3) the radical anion with strong through-space interactions between the redox-active NDI molecules, and 4) the diamagnetic diradical dianion using UV/Vis/NIR, EPR and ENDOR spectroscopies in addition to X-ray crystallography. Despite the unfavorable Coulombic repulsion, the singlet diradical dianion dimer of NDI shows a more pronounced intramolecular π-π stacking interaction when compared with its neutral analog.
111 citations
TL;DR: The one-pot synthesis and electrochemical switching mechanism of a family of electrochemically bistable 'daisy chain' rotaxane switches based on a derivative of the so-called 'blue box' (BB(4+)) tetracationic cyclophane cyclobis(paraquat-p-phenylene) is reported.
Abstract: We report the one-pot synthesis and electrochemical switching mechanism of a family of electrochemically bistable ‘daisy chain’ rotaxane switches based on a derivative of the so-called ‘blue box’ (BB4+) tetracationic cyclophane cyclobis(paraquat-p-phenylene). These mechanically interlocked molecules are prepared by stoppering kinetically the solution-state assemblies of a self-complementary monomer comprising a BB4+ ring appended with viologen (V2+) and 1,5-dioxynaphthalene (DNP) recognition units using click chemistry. Six daisy chains are isolated from a single reaction: two monomers (which are not formally ‘chains’), two dimers, and two trimers, each pair of which contains a cyclic and an acyclic isomer. The products have been characterized in detail by high-field 1H NMR spectroscopy in CD3CN—made possible in large part by the high symmetry of the novel BB4+ functionality—and the energies associated with certain aspects of their dynamics in solution are quantified. Cyclic voltammetry and spectroelectro...
111 citations
TL;DR: How a class of metallosupramolecular cages known as M12L24 polyhedra have been adapted to serve as nanometer-scale containers for solutions of a pseudorotaxane host-guest complex based on a tetracationic cyclophane host, cyclobis(paraquat-p-phenylene) (CBPQT), and a 1,5-dioxynaphthalene (DNP) guest is reported.
Abstract: “Molecular flasks” are well-defined supramolecular cages that can encapsulate one or more molecular guests within their cavities and, in so doing, change the physical properties and reactivities of the guests. Although molecular flasks are powerful tools for manipulating matter on the nanoscale, most of them are limited in their scope because of size restrictions. Recently, however, increasingly large and diverse supramolecular cages have become available with enough space in their cavities for larger chemical systems such as polymers, nanoparticles, and biomolecules. Here we report how a class of metallosupramolecular cages known as M12L24 polyhedra have been adapted to serve as nanometer-scale containers for solutions of a pseudorotaxane host–guest complex based on a tetracationic cyclophane host, cyclobis(paraquat-p-phenylene) (CBPQT4+), and a 1,5-dioxynaphthalene (DNP) guest. Remarkably, the hierarchical integration of pseudorotaxanes and M12L24 superhosts causes the system to express stimulus-respons...
84 citations
TL;DR: The subtle interplay of noncovalent bonding interactions, resulting from the tiny structural variations involving the DXE guests, is responsible for the diverse and highly specific assembly of NDI-Δ.
Abstract: Precise control of molecular assembly is a challenging goal facing supramolecular chemists. Herein, we report the highly specific assembly of a range of supramolecular nanotubes from the enantiomeric triangular naphthalenediimide-based macrocycles (RRRRRR)- and (SSSSSS)-NDI-Δ and a class of similar solvents, namely, the 1,2-dihalo-ethanes and -ethenes (DXEs). Three kinds of supramolecular nanotubes are formed from the columnar stacking of NDI-Δ units with a 60° mutual rotation angle as a result of cooperative [C–H···O] interactions, directing interactions of the [X···X]-bonded DXE chains inside the nanotubes and lateral [X···π] or [π···π] interactions. They include (i) semiflexible infinite nanotubes formed in the gel state from NDI-Δ and (E)-1,2-dichloroethene, (ii) rigid infinite nonhelical nanotubes produced in the solid state from NDI-Δ and BrCH2CH2Br, ClCH2CH2Br, and ClCH2CH2I, and (iii) a pair of rigid tetrameric, enantiomeric single-handed (P)- and (M)-helical nanotubes formed in the solid state fr...
79 citations
TL;DR: While a single pillar[6]arene ring, nestling between two cucurbit[7]uril rings in a series of three hetero[4]rotaxanes, is conformationally mobile in solution, it adopts the energetically most favourable conformation with local C3V symmetry in the solid state.
TL;DR: Enantiopure struts containing pillar[5]arenes incorporating planar chirality have been linked together with Zn4O clusters in order to create metal-organic frameworks that include homochiral active domains and so have the potential to act as a solid support in chiral chromatography.
TL;DR: The template-directed synthesis of BlueCage(6+), a macrobicyclic cyclophane composed of six pyridinium rings fused with two central triazines and bridged by three paraxylylene units, is reported, which makes it a powerful receptor for polycyclic aromatic hydrocarbons (PAHs).
Abstract: We report the template-directed synthesis of BlueCage(6+), a macrobicyclic cyclophane composed of six pyridinium rings fused with two central triazines and bridged by three paraxylylene units. These moieties endow the cage with a remarkably electron-poor cavity, which makes it a powerful receptor for polycyclic aromatic hydrocarbons (PAHs). Upon forming a 1:1 complex with pyrene in acetonitrile, however, BlueCage⋅6 PF6 exhibits a lower association constant Ka than its progenitor ExCage⋅6 PF6. A close inspection reveals that the six PF6(-) counterions of BlueCage(6+) occupy the cavity in a fleeting manner as a consequence of anion-π interactions and, as a result, compete with the PAH guests. This conclusion is supported by a one order of magnitude increase in the Ka value for pyrene in BlueCage(6+) when the PF6(-) counterions are replaced by much bulkier anions. The presence of anion-π interactions is supported by X-ray crystallography, and confirms the presence of a PF6(-) counterion inside its cavity.
TL;DR: The design and production of a supramolecular flashing energy ratchet capable of processing chemical fuel generated by redox changes to drive a ring in one direction relative to a dumbbell toward an energetically uphill state is reported on.
Abstract: A challenge in contemporary chemistry is the realization of artificial molecular machines that can perform work in solution on their environments. Here, we report on the design and production of a supramolecular flashing energy ratchet capable of processing chemical fuel generated by redox changes to drive a ring in one direction relative to a dumbbell toward an energetically uphill state. The kinetics of the reaction pathway juxtapose a low energy [2]pseudorotaxane that forms under equilibrium conditions with a high energy, metastable [2]pseudorotaxane which resides away from equilibrium.
TL;DR: The Golden Jubilee of the introduction by Gottfried Schill and Arthur L tringhaus in 1964 of the newest of (strong) bonds in chemistry at the time is being celebrated this year as the mechanical bond makes its transition from adolescence to adulthood.
Abstract: The Golden Jubilee of the introduction by Gottfried Schill and Arthur L ttringhaus in 1964 of the newest of (strong) bonds in chemistry at the time is being celebrated this year as the mechanical bond makes its transition from adolescence to adulthood. Molecules, of which the catenanes and rotaxanes are the archetypal examples, with mechanical bonds have emerged during their 50year lifespan with ever-increasing frequency—after an induction period that lasted almost two decades—from being little more than intellectual curiosities to all but a small esoteric band of academic outliers and a few fancy-free researchers in the forward-looking industrial corporate laboratories of the day, to becoming one of the cornerstones of molecular nanotechnology.
TL;DR: A cyclic daisy chain dimer based on π-associated donor-acceptor interactions, which can be actuated with either thermal or electrochemical stimuli, is reported herein.
Abstract: Although motor proteins are essential cellular components that carry out biological processes by converting chemical energy into mechanical motion, their functions have been difficult to mimic in artificial synthetic systems. Daisy chains are a class of rotaxanes which have been targeted to serve as artificial molecular machines because their mechanically interlocked architectures enable them to contract and expand linearly, in a manner that is reminiscent of the sarcomeres of muscle tissue. The scope of external stimuli that can be used to control the musclelike motions of daisy chains remains limited, however, because of the narrow range of supramolecular motifs that have been utilized in their templated synthesis. Reported herein is a cyclic daisy chain dimer based on π-associated donor-acceptor interactions, which can be actuated with either thermal or electrochemical stimuli. Molecular dynamics simulations have shown the daisy chain's mechanism of extension/contraction in the ground state in atomistic detail.
TL;DR: The research reported here introduces an innovative design, termed LASO-lock-arm supramolecular ordering-in the form of a modular approach for the development of responsive organic cocrystals, which relies on the use of aromatic electronic donor and acceptor building blocks, carrying complementary rigid and flexible arms, capable of forming hydrogen bonds to amplify the cocrystallization processes.
Abstract: Organic charge transfer cocrystals are inexpensive, modular, and solution-processable materials that are able, in some instances, to exhibit properties such as optical nonlinearity, (semi)conductivity, ferroelectricity, and magnetism. Although the properties of these cocrystals have been investigated for decades, the principal challenge that researchers face currently is to devise an efficient approach which allows for the growth of high-quality crystalline materials, in anticipation of a host of different technological applications. The research reported here introduces an innovative design, termed LASO—lock-arm supramolecular ordering—in the form of a modular approach for the development of responsive organic cocrystals. The strategy relies on the use of aromatic electronic donor and acceptor building blocks, carrying complementary rigid and flexible arms, capable of forming hydrogen bonds to amplify the cocrystallization processes. The cooperativity of charge transfer and hydrogen-bonding interactions ...
TL;DR: A new method of functionalizing pillar[5]arene is developed in which one of the five hydroquinone units is converted into a diaminobenzoquinone analogue, which can be chemically modified yet further in a direction that is orthogonal to the plane of its methylene bridging carbons through the formation of oxazole heterocycles.
Abstract: The recently introduced pillar[n]arenes have provided chemists with receptors that, when incorporated into materials, confer unique properties upon them. The symmetrical rims and cylindrical shape of pillar[5]arene begs the question--can these pillar-like receptors be linked covalently end-to-end in order to create tubular structures by a growth-from-template approach? In our efforts to produce these one-dimensional extended structures, we have developed a new method of functionalizing pillar[5]arene in which one of the five hydroquinone units is converted into a diaminobenzoquinone analogue. The resulting diaminopillar[5]arene derivative, which undergoes a stereochemical inversion process that is slow on the (1)H NMR timescale, can be chemically modified yet further in a direction that is orthogonal to the plane of its methylene bridging carbons through the formation of oxazole heterocycles. This strategy has been employed to create rigid oligomers that resemble one-dimensional tubular arrays. As a proof-of-principle, a rigid pillar[5]arene dimer has been isolated and characterized in the solution state as a 1:1 complex with an extended viologen for which it acts as a receptor.
TL;DR: Thermally driven motions between the neighboring NDI units in the oligorotaxanes influence the passage of electrons through the NDI stacks in a manner reminiscent of the conformationally gated charge transfer observed in DNA.
Abstract: The controlled self-assembly of well-defined and spatially ordered π-systems has attracted considerable interest because of their potential applications in organic electronics. An important contemporary pursuit relates to the investigation of charge transport across noncovalently coupled components in a stepwise fashion. Dynamic oligorotaxanes, prepared by template-directed methods, provide a scaffold for directing the construction of monodisperse one-dimensional assemblies in which the functional units communicate electronically through-space by way of π-orbital interactions. Reported herein is a series of oligorotaxanes containing one, two, three and four naphthalene diimide (NDI) redox-active units, which have been shown by cyclic voltammetry, and by EPR and ENDOR spectroscopies, to share electrons across the NDI stacks. Thermally driven motions between the neighboring NDI units in the oligorotaxanes influence the passage of electrons through the NDI stacks in a manner reminiscent of the conformationally gated charge transfer observed in DNA.
TL;DR: The electrochemical behavior of these three radically configurable isomers demonstrates that a fundamental relationship exists between topology and redox properties.
Abstract: While mechanical bonding stabilizes tetrathiafulvalene (TTF) radical dimers, the question arises: what role does topology play in catenanes containing TTF units? Here, we report how topology, together with mechanical bonding, in isomeric [3]- and doubly interlocked [2]catenanes controls the formation of TTF radical dimers within their structural frameworks, including a ring-in-ring complex (formed between an organoplatinum square and a {2+2} macrocyclic polyether containing two 1,5-dioxynaphthalene (DNP) and two TTF units) that is topologically isomeric with the doubly interlocked [2]catenane. The separate TTF units in the two {1+1} macrocycles (each containing also one DNP unit) of the isomeric [3]catenane exhibit slightly different redox properties compared with those in the {2+2} macrocycle present in the [2]catenane, while comparison with its topological isomer reveals substantially different redox behavior. Although the stabilities of the mixed-valence (TTF2)•+ dimers are similar in the two catenanes...
TL;DR: This review summarizes the work carried out in the laboratory on the second-sphere coordination chemistry of transition metal complexes in the past three decades and significant advances of relevance to theSecond-Sphere coordination Chemistry of square-planar gold complex anions with cyclodextrins are presented.
Abstract: Since the concept of second-sphere coordination of transition metal complexes was introduced by Alfred Werner in 1913, the investigation of the phenomenon has emerged as a major thrust area - a significant part of which is based on the use of transition metal complexes as first coordination spheres as well as macrocycles as second-sphere ligands in promoting the assembly and dictating the main structural features of the second-sphere adducts. In this review, we first of all summarize the work carried out in our laboratory on the second-sphere coordination chemistry of transition metal complexes in the past three decades. Significant advances of relevance to the second-sphere coordination chemistry of square-planar gold complex anions with cyclodextrins are presented as the second part of this review.
TL;DR: This investigation is an investigation of an alternate, through-bond intramolecular electron-transfer pathway involving ExBox(4+) using a combination of transient absorption and femtosecond stimulated Raman spectroscopy (FSRS).
Abstract: Molecules capable of accepting and storing multiple electrons are crucial components of artificial photosynthetic systems designed to drive catalysts, such as those used to reduce protons to hydrogen. ExBox4+, a boxlike cyclophane comprising two π-electron-poor extended viologen units tethered at both ends by two p-xylylene linkers, has been shown previously to accept an electron through space from a photoexcited guest. Herein is an investigation of an alternate, through-bond intramolecular electron-transfer pathway involving ExBox4+ using a combination of transient absorption and femtosecond stimulated Raman spectroscopy (FSRS). Upon photoexcitation of ExBox4+, an electron is transferred from one of the p-xylylene linkers to one of the extended viologen units in ca. 240 ps and recombines in ca. 4 ns. A crystal structure of the doubly reduced species ExBox2+ was obtained.
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TL;DR: In this article, a donor-acceptor cyclophane was synthesized using a template-directed protocol and alkene metathesis as the ring-closing step, which can act as a push-button molecular switch where the co-conformations of the [2] catenane can be controlled either chemically or electrochemically.
Abstract: A donor–acceptor [2]catenane, in which an extended tetracationic cyclophane is mechanically interlocked by a porphyrin-containing macrocycle, was synthesised using a template-directed protocol and alkene metathesis as the ring-closing step. In the ground state of this [2]catenane, the porphyrin ring resides inside the cavity of the cyclophane on account of favourable charge-transfer interactions between the electron-rich porphyrin and the electron-deficient cyclophane. The [2]catenane can act as a push-button molecular switch where the co-conformations of the [2]catenane can be controlled either chemically or electrochemically. Addition of acid protonates the porphyrin ring and a relative circumrotational motion of the macrocycle positions the charged porphyrin ring outside the cavity of the cyclophane. The switch can be reset to its ground-state co-conformation by the addition of base. Electrochemical reduction of the extended bipyridinium units of the cyclophane decreases the strength of the donor–acceptor interactions in the [2]catenane, leading to a loss of recognition between the mechanically interlocked rings. The chemical and electrochemical switching mechanisms are both reversible.
TL;DR: An octacationic homo[2]catenane comprised of two mechanically interlocked cyclobis(paraquat-p-phenylene) rings has been obtained from the oxidation of the septacations monoradical with nitrosonium hexafluoroantimonate.
Abstract: An octacationic homo[2]catenane comprised of two mechanically interlocked cyclobis(paraquat-p-phenylene) rings has been obtained from the oxidation of the septacationic monoradical with nitrosonium hexafluoroantimonate The nanoconfinement of normally repulsive bipyridinium units results in the enforced π-overlap of eight positively charged pyridinium rings in a volume of <125 nm3 In the solid state, the torsional angles around the C–C bonds between the four pairs of pyridinium rings range between 16 and 30°, while the π–π stacking distances between the bipyridinium units are extended for the inside pair and contracted for the pairs on the outside—a consequence of Coulombic repulsion between the inner bipyridinium subunits In solution, irradiation of the [2]catenane at 275 nm results in electron transfer from one of the paraphenylene rings to the inner bipyridinium dimer, leading to the generation of a temporary mixed-valence state within the rigid and robust homo[2]catenane
TL;DR: It is demonstrated that a titanium-oxo cluster, which possesses a unique edge-sharing Ti4O17 octahedron tetramer core, is stabilized by the constraints produced by two orthogonal 1,1'-ferrocenedicarboxylato (fdc) ligands.
Abstract: By introducing steric constraints into molecular compounds, it is possible to achieve atypical coordination geometries for the elements. Herein, we demonstrate that a titanium-oxo cluster [{Ti4(μ4-O)(μ2-O)2}(OPr(i))6(fdc)2], which possesses a unique edge-sharing Ti4O17 octahedron tetramer core, is stabilized by the constraints produced by two orthogonal 1,1'-ferrocenedicarboxylato (fdc) ligands. As a result, a square-planar tetracoordinate oxygen (ptO) can be generated. The bonding pattern of this unusual anti-van't Hoff/Le Bel oxygen, which has been probed by theoretical calculations, can be described by two horizontally σ-bonded 2p(x) and 2p(y) orbitals along with one perpendicular nonbonded 2p(z) orbital. While the two ferrocene units are separated spatially by the ptO with an Fe⋅⋅⋅Fe separation of 10.4 A, electronic communication between them still takes place as revealed by the cluster's two distinct one-electron electrochemical oxidation processes.
TL;DR: In this paper, the synthesis of 3,6-dichloro-, -dibromo-, and -diiodopyromellitic diimides (ACl, ABr, and AI, respectively) has been achieved.
Abstract: The syntheses of 3,6-dichloro-, -dibromo-, and -diiodopyromellitic diimides—ACl, ABr, and AI, respectively—have been achieved. X-Ray crystallography of single crystals of ACl and ABr unveils the formation of extensive halogen-bonding networks in the solid state as a consequence of interactions between the lone pairs on the carbonyl oxygen atoms with the σ-holes of the halogen atoms. Further, the solid-state superstructure of diiodopyromellitic diimide is characterised by the formation of associated halogen-π dimers. The co-crystallisation of ACl or ABr with a 1,5-diaminonaphthalene derivative DN yields co-crystals of a mixed-stack charge-transfer (CT) complex which are supported by an expansive hydrogen-bonded network in addition to halogen-bonded belts that bring adjacent mixed-stacks into association with each other. 2,6-Dimethoxynaphthalene (DO) proved to be an effective CT complement to AI, yielding solvent-free co-crystals with superstructures which are comprised of a 1:2 ratio of AI to DO. This dimeric halogen-bonding motif is reminiscent of the formation of hydrogen-bonded dimers between carboxylic acids.
TL;DR: Acid-catalysed scrambling of the mechanically interlocked components between two different homo[3]rotaxanes affords a statistical mixture of a hetero-rotaxane along with the two homo-3] rotaxanes, indicating that neither selectivity nor cooperativity is operating during the assembly process.
TL;DR: This communication describes a mechanically interlocked molecule (MIM), capable of switchable and reversible linear molecular motion, and its role in drug discovery and drug discovery is described.
Abstract: Artificial muscles are an essential component for the development of next-generation prosthetic devices, minimally invasive surgical tools, and robotics. This communication describes the design, synthesis, and characterisation of a mechanically interlocked molecule (MIM), capable of switchable and reversible linear molecular motion in aqueous solution that mimics muscular contraction and extension. Compatibility with aqueous solution was achieved in the doubly bistable palindromic [3]rotaxane design by using radical-based molecular recognition as the driving force to induce switching.
TL;DR: In this paper, the authors reflect upon the serendipitous discovery of two classes of extended crystalline materials, referred to as cyclodextrin metal-organic frameworks (CD-MOFs) and CD-Bamboo, which offer opportunities for potential applications in the world of industry and commerce.
Abstract: Abstract Cyclodextrins (CDs) – a family of cyclic oligosaccharides – are ideal building blocks for the construction of environmentally benign materials. Herein, we reflect upon the serendipitous discovery of two classes of extended crystalline materials – referred to as cyclodextrin metal-organic frameworks (CD-MOFs) and CD-Bamboo – based on CDs which offer opportunities for potential applications in the world of industry and commerce all the way from sequestering carbon dioxide to extracting gold in an eco-friendly manner. The crucial role of serendipity in scientific research expresses itself two times over at the boundaries between coordination chemistry with materials science.
TL;DR: The synthesis of a donor-acceptor dyad comprising a zinc porphyrin donor and a tetracationic cyclobis(paraquat-p-phenylene) (CBPQT(4+) ) acceptor is described, which reveals the formation of a dimeric motif through the intermolecular coordination between the triazole nitrogen and the central Zn metal of two adjacent units of the dyad.
Abstract: Understanding the mechanism of efficient photoinduced electron-transfer processes is essential for developing molecular systems for artificial photosynthesis. Towards this goal, we describe the synthesis of a donor-acceptor dyad comprising a zinc porphyrin donor and a tetracationic cyclobis(paraquat-p-phenylene) (CBPQT(4+) ) acceptor. The X-ray crystal structure of the dyad reveals the formation of a dimeric motif through the intermolecular coordination between the triazole nitrogen and the central Zn metal of two adjacent units of the dyad. Photoinduced electron transfer within the dyad in MeCN was investigated by femtosecond and nanosecond transient absorption spectroscopy, as well as by transient EPR spectroscopy. Photoexcitation of the dyad produced a weakly coupled ZnP(+.) -CBPQT(3+.) spin-correlated radical-ion pair having a τ=146 ns lifetime and a spin-spin exchange interaction of only 0.23 mT. The long radical-ion-pair lifetime results from weak donor-acceptor electronic coupling as a consequence of having nine bonds between the donor and the acceptor, and the reduction in reorganization energy for electron transfer caused by charge dispersal over both paraquat units within CBPQT(3+.) .