Showing papers in "Accounts of Chemical Research in 2005"
TL;DR: The structures of all 1127 three-periodic extended metal-organic frameworks reported in the Cambridge Structure Database have been analyzed, and their underlying topology has been determined, leading to a system of classification "taxonomy" for interpreting and rationalizing known MOF structures.
Abstract: The structures of all 1127 three-periodic extended metal−organic frameworks (MOFs) reported in the Cambridge Structure Database have been analyzed, and their underlying topology has been determined. It is remarkable that among the almost infinite number of net topologies that are available for MOFs to adopt, only a handful of nets are actually observed. The discovery of this inversion between expected and observed nets led us to deduce a system of classification “taxonomy” for interpreting and rationalizing known MOF structures, as well as those that will be made in future. The origin of this inversion is attributed to the different modes with which MOF synthesis has been approached. Specifically, three levels of complexity are defined that embody rules “grammar” for the design of MOFs and other extended structures. This system accounts for the present proliferation of MOF structures of high symmetry nets, but more importantly, it provides the basis for designing a building block that “codes” for a specif...
2,079 citations
TL;DR: Recent progress in wettability on functional surfaces is reviewed through the cooperation between the chemical composition and the surface micro- and nanostructures, which may bring great advantages in a wide variety of applications in daily life, industry, and agriculture.
Abstract: Biomimetic research indicates that many phenomena regarding wettability in nature, such as the self-cleaning effect on a lotus leaf and cicada wing, the anisotropic dewetting behavior on a rice leaf, and striking superhydrophobic force provided by a water strider's leg, are all related to the unique micro- and nanostructures on the surfaces. It gives us much inspiration to realize special wettability on functional surfaces through the cooperation between the chemical composition and the surface micro- and nanostructures, which may bring great advantages in a wide variety of applications in daily life, industry, and agriculture. This Account reviews recent progress in these aspects.
1,931 citations
TL;DR: The last 15 years of work with the Pd(II)-cornered unit is summarized in this Account, from the spontaneous formation of a Pd4 square metal complex to a family of architectures such as cages, bowls, boxes, tubes, catenanes, and spheres.
Abstract: The [enPd(II)]2+ (en = ethylenediamine) unit has emerged as a versatile building block in molecular self-assembly. In particular, the 90° coordination angle of the metal has been judiciously used in the design of new discrete two- and three-dimensional structures. Our last 15 years of work with the Pd(II)-cornered unit is summarized in this Account, from the spontaneous formation of a Pd4 square metal complex to a family of architectures such as cages, bowls, boxes, tubes, catenanes, and spheres.
1,797 citations
TL;DR: The main features of the interaction are given, and the close similarity with the hydrogen bonding will become apparent, and some heuristic principles are presented to develop a rational crystal engineering based on halogen bonding.
Abstract: Halogen bonding is the noncovalent interaction between halogen atoms (Lewis acids) and neutral or anionic Lewis bases. The main features of the interaction are given, and the close similarity with the hydrogen bonding will become apparent. Some heuristic principles are presented to develop a rational crystal engineering based on halogen bonding. The focus is on halogen-bonded supramolecular architectures given by halocarbons. The potential of the interaction is shown by useful applications in the field of synthetic chemistry, material science, and bioorganic chemistry.
1,673 citations
TL;DR: The combination of mastered chemistry and of computer simulations pushes forward the limits of the classical approach and allows the full determination from powder diffraction data of architectures with cells of several hundred thousand cubic angstroms with hierarchies of giant pores and unprecedented Langmuir surfaces.
Abstract: In the domain of porous solids with inorganic or hybrid frameworks, the combination of mastered chemistry and of computer simulations pushes forward the limits of the classical approach and allows the full determination from powder diffraction data of architectures with cells of several hundred thousand cubic angstroms with hierarchies of giant pores and unprecedented Langmuir surfaces. The different limits induced by this new approach are analyzed.
1,228 citations
TL;DR: This Account details the work on directing the assembly of open-framework structures based on molecules and investigating how the response of nanoporous examples of such materials to guests differs from classical rigid porous systems.
Abstract: Scientific and technological interest in porous materials with molecule-sized channels and cavities has led to an intense search for controlled chemical routes to systems with specific properties. This Account details our work on directing the assembly of open-framework structures based on molecules and investigating how the response of nanoporous examples of such materials to guests differs from classical rigid porous systems. The stabilization of chiral nanoporosity by a hierarchy of interactions that both direct and maintain a helical open-framework structure exemplifies the approach.
1,170 citations
TL;DR: In this paper, a chiral self-assembled M4L6 supramolecular tetrahedron can encapsulate a variety of cationic guests with varying degrees of stereoselectivity.
Abstract: Supramolecular chemistry represents a way to mimic enzyme reactivity by using specially designed container molecules. We have shown that a chiral self-assembled M4L6 supramolecular tetrahedron can encapsulate a variety of cationic guests with varying degrees of stereoselectivity. Reactive iridium guests can be encapsulated, and the C−H bond activation of aldehydes occurs with the host cavity controlling the ability of substrates to interact with the metal center based upon size and shape. In addition, the host container can act as a catalyst by itself. By restricting reaction space and preorganizing the substrates into reactive conformations, it accelerates the sigmatropic rearrangement of enammonium cations.
864 citations
TL;DR: An overview of the rational behind molecular tectonics is presented and a variety of molecular networks based on van der Waals interactions and hydrogen and coordination bonding possessing diverse connectivity and topology are discussed.
Abstract: Molecular networks in the crystalline phase are infinite periodic molecular assemblies formed under self-assembly conditions between self-complementary or complementary tectons. These millimeter-size structures may be regarded as hypermolecules formed by supramolecular synthesis using reversible intertecton interactions. Molecular tectonics, based on molecular recognition events and their iteration, is the approach dealing with design and preparation of molecular networks in the solid state. In this Account, an overview of the rational behind this approach is presented. A variety of molecular networks based on van der Waals interactions and hydrogen and coordination bonding possessing diverse connectivity and topology are discussed.
704 citations
TL;DR: A series of macrocyclic receptors designed to probe the influence of four factors, hydrogen bonding, charge, dimensionality, and topology, on anion binding indicate a number of corollaries with transition-metal coordination chemistry in terms of binding concepts such as the chelate effect and dual valencies.
Abstract: A series of macrocyclic receptors were designed to probe the influence of four factors, hydrogen bonding, charge, dimensionality, and topology, on anion binding. Monocyclic and bicyclic polyammonium and polyamide receptors were synthesized from either 2,2‘-diaminodiethylamine derivatives (dien) or 2,2‘,2‘ ‘-aminoethylamine (tren) building blocks, plus aromatic or heterocyclic spacers. Supramolecular complexes of these hosts with three simple anion topologies were probed: spherical (halides), trigonal planar (nitrate), and tetrahedral (sulfate). Results indicate a number of corollaries with transition-metal coordination chemistry in terms of binding concepts such as the chelate effect and dual valencies, as well as geometries for anion complexes that are strikingly similar to those observed in transition-metal coordination chemistry.
627 citations
TL;DR: This Account focuses on the application of multivalency to supramolecular chemistry in particular and the nanosciences in general.
Abstract: Multivalent interactions, which rely upon noncovalent bonds, are essential ingredients in the mediation of biological processes, as well as in the construction of complex (super)structures for materials applications. A fundamental understanding of multivalency in supramolecular chemistry is necessary not only to construct motors and devices on the nanoscale but also to synthesize model systems to provide insight into how biological processes work. This Account focuses on the application of multivalency to supramolecular chemistry in particular and the nanosciences in general.
563 citations
TL;DR: This strategy is based on the visualization of the structures as combinations of interconnected layered 2-D sheets or subnet tectons and allows ready identification and interpretation of some of the most highly connected and complex architectures yet observed in materials chemistry.
Abstract: Coordination framework polymers derived from lanthanide metal ions with N,N‘-dioxide ligands (4,4‘-bipyridine-N,N‘-dioxide, pyrazine-N,N‘-dioxide, 1,2-bis(pyridin-4-yl)ethane-N,N‘-dioxide, trans-1,2-bis(pyridin-4-yl)ethene-N,N‘-dioxide) exhibit such intricate architectures that a new strategy is required to appreciate and understand their structures. Rather than analyzing the overall structure in terms of the connectivity of individual metal nodes, which can lead in some cases to extremely complex topological treatments, our new strategy is based on the visualization of the structures as combinations of interconnected layered 2-D sheets or subnet tectons. Despite the diversity and relative complexities of many of the structures discussed here, they can all be described by the interconnection of just two types of 2-D subnet tectons, 44 square grids or 63 hexagonal grids. The interconnection of these layered sheets with bridging N,N‘-dioxide molecules gives rise to both 2-D bilayer and 3-D network extended ...
TL;DR: This Account describes some lessons that have been learned about aspects of ligand design and recommends the incorporation of a diverse range of heterocyclic rings and arene cores within the ligands, as well as attention to symmetry considerations.
Abstract: Metallosupramolecular chemistry involves the use of combinations of organic ligands and metals for the construction of both discrete and polymeric aggregates. This Account describes some lessons that we have learned about aspects of ligand design in the course of our work in this area. Specifically, we recommend the incorporation of a diverse range of heterocyclic rings and arene cores within the ligands, as well as attention to symmetry considerations, and offer suggestions for the introduction of chirality and flexibility within the ligands and the exploitation of other weak interactions to assist self-assembly processes.
TL;DR: The course of investigations in this area is described, beginning with the development of a chemical tool kit of building blocks consisting of multiple metals and ligands, which can be rationally mixed and matched to provide structures with a wide range of properties.
Abstract: The weak-link approach (WLA) to supramolecular assemblies allows for the design of multimetallic two- and three-dimensional arrays, host-guest architectures, sensors, catalysts, switches, and signal amplification devices. This Account describes the course of our investigations in this area beginning with the development of a chemical tool kit of building blocks consisting of multiple metals and ligands. These building blocks can be rationally mixed and matched to provide structures with a wide range of properties that have been used to develop functional supramolecular architectures, including chemical sensors and allosteric catalysts.
TL;DR: The potential applications of crystalline chalcogenide superlattices extend beyond traditional areas such as acid catalysis or adsorption-based separation to include shape- or size-selective photocatalysis, solid-state ionics, and electrochemistry.
Abstract: One of the most exciting recent developments concerning molecular architectures is the emerging field of crystalline chalcogenide superlattices that bridges two traditional but distinct areas of research: chalcogenide clusters and porous materials. By combining synthetic and structural concepts in these two areas, many crystalline solids containing spatially organized chalcogenide clusters have been created that exhibit varied properties ranging from microporosity, fast ion conductivity, and photoluminescence to narrow and tunable electronic band gaps. The potential applications of these materials extend beyond traditional areas such as acid catalysis or adsorption-based separation to include shape- or size-selective photocatalysis, solid-state ionics, and electrochemistry.
TL;DR: The fullerene-porphyrin interaction underlies successful chromatographic separations of fullerenes, and there are promising applications in the areas of porous framework solids and photovoltaic devices.
Abstract: Porphyrins and fullerenes are spontaneously attracted to each other. This new supramolecular recognition element can be used to construct discrete host−guest complexes, as well as ordered arrays of interleaved porphyrins and fullerenes. The fullerene−porphyrin interaction underlies successful chromatographic separations of fullerenes, and there are promising applications in the areas of porous framework solids and photovoltaic devices.
TL;DR: The multiple ferritin functions combine pore, channel, and catalytic functions in compact protein structures required for life and disease response.
Abstract: Ferritins are spherical, cage-like proteins with nanocavities formed by multiple polypeptide subunits (four-helix bundles) that manage iron/oxygen chemistry. Catalytic coupling yields diferric oxo/hydroxo complexes at ferroxidase sites in maxi-ferritin subunits (24 subunits, 480 kDa; plants, animals, microorganisms). Oxidation occurs at the cavity surface of mini-ferritins/Dps proteins (12 subunits, 240 kDa; bacteria). Oxidation products are concentrated as minerals in the nanocavity for iron-protein cofactor synthesis (maxi-ferritins) or DNA protection (mini-ferritins). The protein cage and nanocavity characterize all ferritins, although amino acid sequences diverge, especially in bacteria. Catalytic oxidation/di-iron coupling in the protein cage (maxi-ferritins, 480 kDa; plants, bacteria and animal cell-specific isoforms) or on the cavity surface (mini-ferritins/Dps proteins, 280 kDa; bacteria) initiates mineralization. Gated pores (eight or four), symmetrically arranged, control iron flow. The multiple ferritin functions combine pore, channel, and catalytic functions in compact protein structures required for life and disease response.
TL;DR: In this article, it was shown that the [HIPTN3N]Mo system can reduce dinitrogen to ammonia in the presence of protons and electrons at room temperature and pressure.
Abstract: As far as we are aware, the [HIPTN3N]Mo system and some of its variations are the only nonenzymatic systems that will reduce dinitrogen catalytically and selectively to ammonia in the presence of protons and electrons at room temperature and pressure. We now can be relatively certain that reduction is accomplished at a single Mo center in a manner that so far appears to be analogous (approximately) to that proposed by Chatt and his group, with an important difference being that the highest possible oxidation states are involved (Mo(III) to Mo(VI)) in the cycle. Conversion of Mo(NH3) to Mo(N2) appears to be one of the slow steps in the successful reductions, in part because ammonia is an inhibitor. Although the catalytic system we have developed does not involve biologically relevant ligands, reduction of dinitrogen to ammonia in such a simple “artificial” Mo system suggests that Mo is exceptional, as Chatt suspected, in its ability to reduce dinitrogen, although it probably is not unique. Whether dinitrogen is reduced at molybdenum in FeMo nitrogenase is still speculative, although it is attractive to propose that it is. It is possible that dinitrogen is reduced at V or Fe when they substitute for Mo. It may prove to be considerably more difficult to design non-enzymatic V or Fe systems that reduce dinitrogen catalytically under conditions similar to those used in the [HIPTN3N]Mo reactions, primarily because V and Fe are less efficient than Mo. One also cannot state that dinitrogen must be reduced at low temperature and pressure only in the manner found in [HIPTN3N]Mo systems. However, at the same time one should ponder whether the sheer complexity of catalytic dinitrogen reduction to ammonia with protons and electrons automatically severely limits mechanistic alternatives under mild conditions. Finally, it is also interesting to speculate what other “high oxidation state” chemistry and what other catalytic reactions can be developed with complexes that contain the [HIPTN3N]3− ligand system.
TL;DR: Using various polyfunctionalized porphyrins, this work has created porous solids that are thermally robust and that retain their internal porosity upon loss of solvates.
Abstract: Metalloporphyrins are exceedingly useful building blocks for the design and synthesis of molecularly based solids. The use of hydrogen bonding or metal ion coordination provides a wide range of framework solids. Using various polyfunctionalized porphyrins, we have created porous solids that are thermally robust and that retain their internal porosity upon loss of solvates. Their pore dimensions are comparable to zeolites, and they show shape and size selectivity in sorption of guest molecules and in epoxidation of alkenes.
TL;DR: The ultimate goal of using these systems to prepare practical photoelectrochemical devices is discussed, and a cell with a monochromatic efficiency of 8.5% conversion of light into current is illustrated.
Abstract: This Account presents recent advances in the design, synthesis, characterization, and potential applications of new hybrid materials based on carbon nanotube and electron donors. Fast charge separation and slow charge recombination are consistently observed in a variety of composites that contain porphyrin derivatives. The ultimate goal of using these systems to prepare practical photoelectrochemical devices is discussed, and a cell with a monochromatic efficiency of 8.5% conversion of light into current is illustrated.
TL;DR: This Account shows how comparative studies aiming at modulating the coordinating properties of functional ligands for a metal, such as nickel, which is used in industrial processes, lead to beneficial effects in catalytic ethylene oligomerization.
Abstract: Catalytic ethylene oligomerization represents a topic of considerable current academic and industrial interest, in particular for the production of linear α-olefins in the C4−C10 range, whose demand is growing fast. Identifying and fine-tuning the parameters that influence the activity and selectivity of metal catalysts constitute major challenges at the interface between ligand design, coordination/organometallic chemistry, and homogeneous catalysis. In this Account, we show how comparative studies aiming at modulating the coordinating properties of functional ligands for a metal, such as nickel, which is used in industrial processes, lead to beneficial effects in catalytic ethylene oligomerization.
TL;DR: The fact that, as in the natural system, after self-assembly, concentration quenching is not operating due to the very orderly manner in which the chromophores are positioned lends hope for applications in artificial devices, such as hybrid solar cells.
Abstract: There is much diversity in the way in which photosynthetic organisms harvest sunlight. In chromophore−protein complexes, an exact orientation of pigments by the protein matrix ensures an efficient stepwise energy transfer to the reaction center where charge separation occurs. The charge separation and subsequent electron transfer steps are, however, very similar in all organisms, proving that there must exist a common ancestor. The architectural principle of chromophore−protein complexes is too complicated to be replicated in artificial light-harvesting devices. A simpler principle employs self-assembling chromophores that early green photosynthetic bacteria use in their chlorosomal antenna systems. Efforts in mimicking this self-assembly algorithm with fully synthetic pigments are presented. The fact that, as in the natural system, after self-assembly, concentration quenching is not operating due to the very orderly manner in which the chromophores are positioned lends hope for applications in artificial...
TL;DR: The combined results of NMR spectroscopy, X-ray crystallography, and various biochemical tools provide incontrovertible evidence that dinuclear complexes are favorably poised to bind to purine nucleobases, DNA fragments, and double-stranded DNA.
Abstract: This Account summarizes the DNA binding properties of anticancer active dinuclear Rh, Re, and Ru compounds. The combined results of NMR spectroscopy, X-ray crystallography, and various biochemical tools provide incontrovertible evidence that dinuclear complexes are favorably poised to bind to purine nucleobases, DNA fragments, and double-stranded DNA. Moreover, direct DNA photocleavage in vitro is effected by dirhodium compounds in the presence of electron acceptors in solution or directly attached to the dirhodium core. This research has provided valuable insight in the interactions of dinuclear compounds with DNA, knowledge that is an excellent backdrop for rational design of promising dinuclear drugs.
TL;DR: Periodic mesoporous organosilicas (PMOs) represent an exciting new class of organic−inorganic nanocomposites targeted for a broad range of applications such as catalysis and sensing, separations, and microelectronics.
Abstract: Periodic mesoporous organosilicas (PMOs) represent an exciting new class of organic−inorganic nanocomposites targeted for a broad range of applications such as catalysis and sensing, separations, and microelectronics. Their hallmark is the presence of organic bridging groups incorporated into the channel walls of an ordered nanoporous structure, which represents a useful tool to finely tune the chemical and physical properties of the materials. We discuss the history of the discovery and development of the PMOs emphasizing the most important recent advancements regarding compositions and structures, morphologies, and properties. Furthermore, we present an outlook about the promising future perspectives of PMOs that result from the latest developments in this field.
TL;DR: The simple, well-understood coordination chemistry of the cyanide ligand is of significant utility in the design of new single-molecule magnets, facilitating creation of high-spin ground states with axial magnetic anisotropy.
Abstract: The simple, well-understood coordination chemistry of the cyanide ligand is of significant utility in the design of new single-molecule magnets. Its preference for bridging two transition metals in a linear M‘−CN−M geometry permits the use of multidentate blocking ligands in directing the assembly of specific molecular architectures. This approach has been employed in the synthesis of numerous high-nuclearity constructs, including simple cubic M4M‘4(CN)12 and face-centered cubic M8M‘6(CN)24 coordination clusters, as well as some unexpected cluster geometries featuring as many as 27 metal centers. The ability to substitute a range of different transition metal ions into these structures enables adjustment of their magnetic properties, facilitating creation of high-spin ground states with axial magnetic anisotropy. To date, at least four different cyano-bridged single-molecule magnets have been characterized, exhibiting spin-reversal barriers as high as 25 cm-1. Ultimately, it is envisioned that this strate...
TL;DR: The present Account pertains to the recent developments in the materials chemistry of squaraines, highlighting the contributions to the study ofSquaraine-based near-IR dyes, low band gap polymers, and cation sensors.
Abstract: Squaraines belong to an important class of organic dyes with intense absorption and emission properties in the visible to near-IR wavelength range. The optical properties of squaraines, which are sensitive to the surrounding medium, make them ideal candidates to photophysists to study the excited-state properties and to material chemists for designing a variety of materials that are useful for wide-ranging applications. The present Account pertains to the recent developments in the materials chemistry of squaraines, highlighting our contributions to the study of squaraine-based near-IR dyes, low band gap polymers, and cation sensors.
TL;DR: Continuous and batch microwave reactors were constructed for efficient, "green" synthesis with low-boiling solvents at high temperature in closed vessels and complementary interactive software for calculating optimal conditions was developed.
Abstract: Continuous and batch microwave reactors were constructed for efficient, "green" synthesis with low-boiling solvents at high temperature in closed vessels. Capabilities for rapid heating and cooling, concurrent heating and cooling, and differential heating facilitated novel chemical reactions and processes. Commercial microwave systems based on these developments are available. Times required for conventional reactions typically are decreased by 2-3 orders of magnitude. Green processes also have resulted through use of less or no catalyst, readily recyclable solvents, or media and yields that are often higher than normal. Complementary interactive software for calculating optimal conditions was developed.
TL;DR: This Account looks at the birth of a new generation of silica nanocomposites using polyhedral oligomeric silsesquioxanes, a promising nanoscale silica particle with particular use in cardiovascular interventional devices.
Abstract: The unique properties of nanocomposites have seen them creating the next revolution in materials science. Their quantal properties as a result of their size have given them unique physical characteristics, previously not possible because of classical physical laws. There is now evidence that these may also extend into the world of biology and medicine. In this Account, we look at the birth of a new generation of silica nanocomposites using polyhedral oligomeric silsesquioxanes, a promising nanoscale silica particle with particular use in cardiovascular interventional devices.
TL;DR: P pH-dependent micellization and pH- dependent micelle-hollow-sphere transition are realized in water-soluble graft copolymers driven by complexation and decomplexation between the main chain and grafts.
Abstract: We succeeded recently in developing a series of new pathways to polymeric micelles and hollow spheres via intermolecular specific interactions. A new micellization mechanism of block copolymers was realized by using the specific interaction between a low molecular weight compound and one of the blocks in low-polarity solvents. Many more successes have been achieved by our "block copolymer-free" strategies. We are now able to use homopolymers, random copolymers, oligomers, etc. as building blocks to construct noncovalently connected micelles (NCCM), in which the core and shell are connected by hydrogen bonding. Some of such NCCMs are readily converted further into hollow spheres by cross-linking the shell and then switching the medium to one that dissolves the core. Rigid polymer chains and their complementary homopolymers can directly assemble into large hollow spheres thanks to the propensity to parallel packing of the rigid chains. In addition, some of the NCCMs show perfect stimuli-responsive properties. pH-dependent micellization and pH-dependent micelle-hollow-sphere transition are realized in water-soluble graft copolymers driven by complexation and decomplexation between the main chain and grafts.
TL;DR: Urea-based ligands have been developed that create rigid organic frameworks when bonded to metal ions that position hydro-gen bond donors proximal to metal ion(s) to form specific chem-ical microenvironments.
Abstract: Hydrogen bonds influence secondary coordination spheres around metal ions in many proteins. To duplicate these features of molecular architecture in synthetic systems, urea-based ligands have have been developed that create rigid organic frameworks when bonded to metal ions. These frameworks position hydro-gen bond donors proximal to metal ion(s) to form specific chem-ical microenvironments. Iron(II) and manganese(II) complexes with constrained cavities activate O2, yielding MIII (MIII = Fe and Mn) complexes with terminal oxo ligands. Installation of anionic sites within the cavity assists the formation of complexes with MII/III−OH and MIII−O units derived directly from water. Opening the cavity promotes M(μ-O)2M rhombs, as illustrated by isolation of a cobalt(III) analogue, the stability of which is promoted by the hydrogen bonds surrounding the bridging oxo ligands.
TL;DR: A theoretical model based on the generalized Langevin equation (GLE) treatment of Kramers' barrier crossing problem for chemical reactions accounts naturally for the observation of dynamic disorder and highly dispersed kinetics.
Abstract: Recent single-molecule enzymology measurements with improved statistics have demonstrated that a single enzyme molecule exhibits large temporal fluctuations of the turnover rate constant at a broad range of time scales (from 1 ms to 100 s). The rate constant fluctuations, termed as dynamic disorder, are associated with fluctuations of the protein conformations observed on the same time scales. We discuss the unique information extractable from these experiments and the reconciliation of these observations with ensemble-averaged Michaelis−Menten equation. A theoretical model based on the generalized Langevin equation (GLE) treatment of Kramers' barrier crossing problem for chemical reactions accounts naturally for the observation of dynamic disorder and highly dispersed kinetics.