Self-assembly of a novel macrotricyclic Pd(II) metallocage encapsulating a nitrate ion.
TL;DR: Complexation of the ligand 1 with Pd(NO3)2 leads to the self-assembly of a very stable M2L4 type macrotricyclic cage that encapsulates a nitrate ion inside its cavity.
About: This article is published in Chemical Communications.The article was published on 2001-01-01. It has received 117 citations till now. The article focuses on the topics: Ligand.
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TL;DR: In the early 1960s, the discovery of crown ethers and spherands by Pedersen, Lehn, and Cram3 led to the realization that small, complementary molecules can be made to recognize each other through non-covalent interactions such as hydrogen-bonding, charge-charge, donor-acceptor, π-π, van der Waals, hydrophilic and hydrophobic interactions to achieve these highly complex and often symmetrical architectures as mentioned in this paper.
Abstract: Fascination with supramolecular chemistry over the last few decades has led to the synthesis of an ever-increasing number of elegant and intricate functional structures with sizes that approach nanoscopic dimensions Today, it has grown into a mature field of modern science whose interfaces with many disciplines have provided invaluable opportunities for crossing boundaries both inside and between the fields of chemistry, physics, and biology This chemistry is of continuing interest for synthetic chemists; partly because of the fascinating physical and chemical properties and the complex and varied aesthetically pleasing structures that supramolecules possess For scientists seeking to design novel molecular materials exhibiting unusual sensing, magnetic, optical, and catalytic properties, and for researchers investigating the structure and function of biomolecules, supramolecular chemistry provides limitless possibilities Thus, it transcends the traditional divisional boundaries of science and represents a highly interdisciplinary field
In the early 1960s, the discovery of ‘crown ethers’, ‘cryptands’ and ‘spherands’ by Pedersen,1 Lehn,2 and Cram3 respectively, led to the realization that small, complementary molecules can be made to recognize each other through non-covalent interactions such as hydrogen-bonding, charge-charge, donor-acceptor, π-π, van der Waals, etc Such ‘programmed’ molecules can thus be self-assembled by utilizing these interactions in a definite algorithm to form large supramolecules that have different physicochemical properties than those of the precursor building blocks Typical systems are designed such that the self-assembly process is kinetically reversible; the individual building blocks gradually funnel towards an ensemble that represents the thermodynamic minimum of the system via numerous association and dissociation steps By tuning various reaction parameters, the reaction equilibrium can be shifted towards the desired product As such, self-assembly has a distinct advantage over traditional, stepwise synthetic approaches when accessing large molecules
It is well known that nature has the ability to assemble relatively simple molecular precursors into extremely complex biomolecules, which are vital for life processes Nature’s building blocks possess specific functionalities in configurations that allow them to interact with one another in a deliberate manner Protein folding, nucleic acid assembly and tertiary structure, phospholipid membranes, ribosomes, microtubules, etc are but a selective, representative example of self-assembly in nature that is of critical importance for living organisms Nature makes use of a variety of weak, non-covalent interactions such as hydrogen–bonding, charge–charge, donor–acceptor, π-π, van der Waals, hydrophilic and hydrophobic, etc interactions to achieve these highly complex and often symmetrical architectures In fact, the existence of life is heavily dependent on these phenomena The aforementioned structures provide inspiration for chemists seeking to exploit the ‘weak interactions’ described above to make scaffolds rivaling the complexity of natural systems
The breadth of supramolecular chemistry has progressively increased with the synthesis of numerous unique supramolecules each year Based on the interactions used in the assembly process, supramolecular chemistry can be broadly classified in to three main branches: i) those that utilize H-bonding motifs in the supramolecular architectures, ii) processes that primarily use other non-covalent interactions such as ion-ion, ion-dipole, π–π stacking, cation-π, van der Waals and hydrophobic interactions, and iii) those that employ strong and directional metal-ligand bonds for the assembly process However, as the scale and degree of complexity of desired molecules increases, the assembly of small molecular units into large, discrete supramolecules becomes an increasingly daunting task This has been due in large part to the inability to completely control the directionality of the weak forces employed in the first two classifications above Coordination-driven self-assembly, which defines the third approach, affords a greater control over the rational design of 2D and 3D architectures by capitalizing on the predictable nature of the metal-ligand coordination sphere and ligand lability to encode directionality Thus, this third strategy represents an alternative route to better execute the “bottom-up” synthetic strategy for designing molecules of desired dimensions, ranging from a few cubic angstroms to over a cubic nanometer For instance, a wide array of 2D systems: rhomboids, squares, rectangles, triangles, etc, and 3D systems: trigonal pyramids, trigonal prisms, cubes, cuboctahedra, double squares, adamantanoids, dodecahedra and a variety of other cages have been reported As in nature, inherent preferences for particular geometries and binding motifs are ‘encoded’ in certain molecules depending on the metals and functional groups present; these moieties help to control the way in which the building blocks assemble into well-defined, discrete supramolecules4
Since the early pioneering work by Lehn5 and Sauvage6 on the feasibility and usefulness of coordination-driven self-assembly in the formation of infinite helicates, grids, ladders, racks, knots, rings, catenanes, rotaxanes and related species,7 several groups - Stang,8 Raymond,9 Fujita,10 Mirkin,11 Cotton12 and others13,14 have independently developed and exploited novel coordination-based paradigms for the self-assembly of discrete metallacycles and metallacages with well-defined shapes and sizes In the last decade, the concepts and perspectives of coordination-driven self-assembly have been delineated and summarized in several insightful reviews covering various aspects of coordinationdriven self-assembly15 In the last decade, the use of this synthetic strategy has led to metallacages dubbed as “molecular flasks” by Fujita,16 and Raymond and Bergman,17 which due to their ability to encapsulate guest molecules, allowed for the observation of unique chemical phenomena and unusual reactions which cannot be achieved in the conventional gas, liquid or solid phases Furthermore, these assemblies found applications in supramolecular catalysis18,19 and as nanomaterials as developed by Hupp20 and others21,22
This review focuses on the journey of early coordination-driven self-assembly paradigms to more complex and discrete 2D and 3D supramolecular ensembles over the last decade We begin with a discussion of various approaches that have been developed by different groups to assemble finite supramolecular architectures The subsequent sections contain detailed discussions on the synthesis of discrete 2D and 3D systems, their functionalizations and applications
2,388 citations
TL;DR: This tutorial review deals with the design, synthesis and host-guest chemistry of discrete coordination cages built according to the combination of pyridyl ligands and square-planar Pd(ii) or Pt(II) cations for the realization of supramolecular self-assemblies.
Abstract: The combination of pyridyl ligands and square-planar Pd(II) or Pt(II) cations has proven to be a very reliable recipe for the realization of supramolecular self-assemblies. This tutorial review deals with the design, synthesis and host–guest chemistry of discrete coordination cages built according to this strategy. The focus is set on structures obeying the formula [PdnL2n] (n = 2–4). The most discussed ligands are bent, bis-monodentate bridges having their two donor sites pointing in the same direction. The structures of the resulting cages range from simple globules over intertwined knots to interpenetrated dimers featuring three small pockets instead of one large cavity. The cages have large openings that allow small guest molecules to enter and leave the cavities. Most structures are cationic and thus favour the uptake of anionic guests. Some examples of host–guest complexes are discussed with emphasis on coencapsulation and allosteric binding phenomena. Aside from cages in which the ligands have only a structural role, some examples of functional ligands based on photo- and redox-active backbones are presented.
560 citations
TL;DR: Three angular ditopic ligands (1,3-bis(benzimidazol-1-ylmethyl)-4,6-dimethylbenzene L(1), 1,3/2, and 1,4/2 are shape-specific designed ligands, representing an alternative strategy to assembling a trigonal prism, and three structures assembled from three linearly coordinated Ag(+) or Cu(+) ions and two tripodal ligands are presented.
Abstract: Three angular ditopic ligands (1,3-bis(benzimidazol-1-ylmethyl)-4,6-dimethylbenzene L1, 1,3-bis(benzimidazol-1-ylmethyl)-2,4,6-trimethylbenzene L2, and 1,4-bis(benzimidazol-1-ylmethyl)-2,3,5,6-tetramethylbenzene L3) and one tripodal ligand 1,3,5-tris(benzimidazol-1-ylmethyl)-2,4,6-trimethylbenzene L4 have been prepared. Reaction of these shape-specific designed ligands with different metal salts affords a series of discrete molecular architectures: [Ag2L12](BF4)2 1, [Ag2L22](CF3SO3)2 2, [CF3SO3- ⊂ Ag2L32]CF3SO3 3, [CF3SO3- ⊂ Ag2L33]CF3SO3 4, [ClO4- ⊂ Cu2L24](ClO4)3 5, [4H2O ⊂ Ni2L24Cl4]·6H2O 6, [BF4- ⊂ Ag3L42](BF4)2 7, [ClO4- ⊂ Ag3L42](ClO4)2 8, and [CuI32- ⊂ Cu3L42]2[Cu2I4] 9. The compounds were characterized by elemental analysis, ESI-MS, IR, and NMR spectroscopy, and X-ray crystallography. 1 is a dinuclear metallacycle with 2-fold rotational symmetry in which two syn-conformational L1ligands are connected by two linearly coordinated Ag+ ions. 2 and 3 are structurally related, consisting of rectangular...
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1,231 citations
TL;DR: In this article, a hollow, roughly spherical supramolecular framework by selfassembly was constructed from ten species: four organic ligands held together by six metal ions, and four adamantyl carboxylate ions can be encapsulated within this selfassembling cage.
Abstract: THE synthesis of hollow, nanometrescale molecular "container compounds1,2 makes possible the creation of localized chemical microenvironments with properties different from those of the bulk phases; such compounds can be used, for example, to encapsulate otherwise unstable molecular species3. Container compounds have previously been prepared by conventional chemical synthesis1,2. Here we report the construction of a hollow, roughly spherical supramolecular framework by selfassembly4–8. The framework, which is ∼2–5 nm in diameter, is constructed from ten species: four organic ligands held together by six metal ions. It has tetrahedral symmetry, and has a large central void, in which guest molecules can be accommodated. We show that four adamantyl carboxylate ions can be encapsulated within this selfassembling cage.
823 citations
TL;DR: In this paper, the preparation and crystal structure of a three-dimensional supramolecular complex that is stabilized by an intricate array of non-covalent interactions involving contributions from solvent water clusters, most notably a water decamer ((H2O) with an ice-like molecular arrangement.
Abstract: Chemical self-assembly is the process by which ‘programmed’ molecular subunits spontaneously form complex supramolecular frameworks1,2. This approach has been applied to many model systems, in which hydrogen bonds3,4, metal–ligand coordination5 or other non-covalent interactions6 typically control the self-assembly process. In biology, self-assembly is generally dynamic and depends on the cooperation of many such non-covalent interactions. Water can play an important role in these biological self-assembly processes, for example by stabilizing the native conformation of biopolymers7,8,9. Hydrogen-bonded (H2O)n clusters10,11 can play an important role in stabilizing some supramolecular species, both natural and synthetic, in aqueous solution. Here we report the preparation and crystal structure of a self-assembled, three-dimensional supramolecular complex that is stabilized by an intricate array of non-covalent interactions involving contributions from solvent water clusters, most notably a water decamer ((H2O)10) with an ice-like molecular arrangement. These findings show that the degree of structuring that can be imposed on water by its surroundings, and vice versa, can be profound.
497 citations
TL;DR: The successful demonstration of such a phenomenon in a coordination approach to a three-dimensional cagelike Pd(II) complex 1?-6 is reported, in which specific substrates induce the organization of the recognition site of a receptor.
Abstract: Instead of the lock-and-key model, current understanding of molecular recognition in a biological system is based on the \"induced-fit'' mechanism, in which specific substrates induce the organization of the recognition site of a receptor. Although models for induced-fit have been provided by flexible artificial hosts which have restricted conformations only if they recognize a specific guest,' there are few examples of induced-fit models in which a guest induces the organization of a host i t ~ e l f . ~ . ~ Reported here is the successful demonstration of such a phenomenon in a coordination approach to a three-dimensional cagelike Pd(II) complex 1?-6 Thus, the complex I assembles in high yields only in the presence of specific guest molecules (Scheme 1). A tridentate ligand 1,3,5-tris(4-pyridy1methyl)benzene' (2,6 mM) was treated with (en)Pd(N03)2* (3, 9 mM) and sodium 4-methoxyphenylacetate (4*Na, 15 mM) at ambient temperature in water. The NMR spectrum, obtained by a control experiment carried out in DzO, showed the assembly of a single component in a high yield ('90%). Characterization of this component as the cagelike complex 1 mainly follows from its electrospray ionization mass spectroscopy (ESI-MS)9%'0 and NMR.\" In
310 citations