Macromolecules containing bipyridine and terpyridine metal complexes: towards metallosupramolecular polymers

The ability of a broad range of N-heterocycles to act as very effective and stable complexation agents for several transition metal ions, such as cobalt(II), copper(II), nickel(II), and ruthenium(II), has long been known in analytical chemistry. This behavior was later utilized in supramolecular chemistry for the construction of highly sophisticated architectures, such as helicates, racks, and grids. The discovery of macromolecules by Staudinger in 1922 opened up avenues towards sophisticated materials with properties hitherto completely unknown. In the last few decades, the combination of macromolecular and supramolecular chemistry has been attempted by developing metal-complexing and metal-containing polymers for a wide variety of applications that range from filtration to catalysis. The stability of the polymer-metal complex is a fundamental requirement for such applications. In this respect, the use of bi- and terpyridines as chelating ligands is highly promising, since these molecules are known to form highly stable complexes with interesting physical properties with transition-metal ions. A large number of different structures have been designed for many different applications, but polymers based on the application of coordinative forces have been prepared in a few cases only. Furthermore, the synthetic procedures applied frequently resulted in low yields. During the last few years, strong efforts have been made in the direction of self-assembling and supramolecular polymers as novel materials with "intelligent" and tunable properties. In this review, an overview of this active area at the interface of supramolecular and macromolecular chemistry is given.     

Hierarchically imprinted sorbents

A double imprinting methodology was developed to synthesize novel materials with hierarchical structures. On the microporous level (1-3 A), metal ions served as template. On the mesoporous level (diameters of 25-40 A), micellar structures produced by self-assembly of surfactant molecules were used as templates. Removal of both metal ions and surfactant micelles resulted in the formation of imprints with different sizes within the silica matrix, each with a specific function. This research opens vast opportunities for the applications of ordered mesoporous materials in the area of molecular recognition such as separations, chemical sensors, and catalysts.     

Dynamic covalent chemistry

Dynamic covalent chemistry relates to chemical reactions carried out reversibly under conditions of equilibrium control. The reversible nature of the reactions introduces the prospects of "error checking" and "proof-reading" into synthetic processes where dynamic covalent chemistry operates. Since the formation of products occurs under thermodynamic control, product distributions depend only on the relative stabilities of the final products. In kinetically controlled reactions, however, it is the free energy differences between the transition states leading to the products that determines their relative proportions. Supramolecular chemistry has had a huge impact on synthesis at two levels: one is noncovalent synthesis, or strict self-assembly, and the other is supramolecular assistance to molecular synthesis, also referred to as self-assembly followed by covalent modification. Noncovalent synthesis has given us access to finite supermolecules and infinite supramolecular arrays. Supramolecular assistance to covalent synthesis has been exploited in the construction of more-complex systems, such as interlocked molecular compounds (for example, catenanes and rotaxanes) as well as container molecules (molecular capsules). The appealing prospect of also synthesizing these types of compounds with complex molecular architectures using reversible covalent bond forming chemistry has led to the development of dynamic covalent chemistry. Historically, dynamic covalent chemistry has played a central role in the development of conformational analysis by opening up the possibility to be able to equilibrate configurational isomers, sometimes with base (for example, esters) and sometimes with acid (for example, acetals). These stereochemical "balancing acts" revealed another major advantage that dynamic covalent chemistry offers the chemist, which is not so easily accessible in the kinetically controlled regime: the ability to re-adjust the product distribution of a reaction, even once the initial products have been formed, by changing the reaction's environment (for example, concentration, temperature, presence or absence of a template). This highly transparent, yet tremendously subtle, characteristic of dynamic covalent chemistry has led to key discoveries in polymer chemistry. In this review, some recent examples where dynamic covalent chemistry has been demonstrated are shown to emphasise the basic concepts of this area of science.     

Metal-mediated reactivity in the organic solid state: from self-assembled complexes to metal-organic frameworks

The purpose of this tutorial review is to address the use of metal ions to mediate reactions in the organic solid state. We describe metal complexes and coordination networks that facilitate dimerizations, oligomerizations and polymerizations of olefins and acetylenes via irradiation (e.g. ultraviolet (UV) and (60)Co gamma-rays) and thermal annealing. We show how metal ions can be utilized to direct the formation of polymers and molecules. We also describe how supramolecular chemistry has recently influenced dimerization processes in self-assembled metal-organic solids.     

The Role of Guest Molecules in the Self-assembly of Metal—ligand Clusters

Abstract

Understanding the self-assembly of nanoscale metal—ligand clusters is an important research area in supramolecular chemistry, especially, if one wishes to develop a truly predictive design strategy for synthesizing these nanoscale clusters. As the building blocks for forming these clusters have become larger and more complex, spacious clusters have been synthesized which often contain large cavities. These assemblies can house guest molecules which play a previously uncharacterized role in the self-assembly processes. We seek to analyze this role: do these guest molecules act as templates? Are the guest molecules necessary for cluster formation? Does the guest drive cluster assemble by forming a stable host—guest complex with the cluster? Must a truly rational design strategy for forming metal—ligand clusters incorporate the use of templates? The role of guest molecules in the self-assembly of nanoscale coordination clusters is reviewed in this article.     

Pre‐Incubation of Auric Acid with DNA Is Unnecessary for the Formation of DNA‐Templated Gold Nanoclusters

The rationale for the preparation of DNA‐templated gold nanoclusters (DNA‐Au NCs) has not been well understood, thereby slowing down the advancement of the synthesis and applications of DNA‐Au NCs. The interaction between metal ions and the DNA template seems to be the key factor for the successful preparation of DNA‐templated metal nanoclusters. With the help of circular dichroism in this contribution, we put efforts into interrogating the necessity of pre‐incubation of HAuCl₄ with poly‐adenine template in the formation of Au NCs by citrate reduction. Our results revealed that the pre‐incubation of HAuCl₄ with poly‐adenine is not favorable for the formation of Au NCs, which is distinctly different from the formation process for silver nanoclusters. It is our hope that this study can provide guidance in the preparation of Au NCs with more DNA templates.     

Recent advances and perspectives on supramolecular radical cages

Supramolecular radical chemistry has been emerging as a cutting-edge interdisciplinary field of traditional supramolecular chemistry and radical chemistry in recent years. The purpose of such a fundamental research field is to combine traditional supramolecular chemistry and radical chemistry together, and take the benefit of both to eventually create new molecules and materials. Recently, supramolecular radical cages have been becoming one of the most frontier and challenging research focuses in the field of supramolecular chemistry. In this Perspective, we give a brief introduction to organic radical chemistry, supramolecular chemistry, and the emerging supramolecular radical chemistry along with their history and application. Subsequently, we turn to the main part of this topic: supramolecular radical cages. The design and synthesis of supramolecular cages consisting of redox-active building blocks and radical centres are summarized. The host–guest interactions between supramolecular (radical) cages and organic radicals are also surveyed. Some interesting properties and applications of supramolecular radical cages such as their unique spin–spin interactions and intriguing confinement effects in radical-mediated/catalyzed reactions are comprehensively discussed and highlighted in the main text. The purpose of this Perspective is to help students and researchers understand the development of supramolecular radical cages, and potentially to stimulate innovation and creativity and infuse new energy into the fields of traditional supramolecular chemistry and radical chemistry as well as supramolecular radical chemistry.

This Perspective summarizes the recent developments of supramolecular radical cages including the design and synthesis of radical cages, their interesting host–guest spin–spin interactions and applications in radical-mediated/catalyzed reactions.     

Multidentate carborane-containing Lewis acids and their chemistry: mercuracarborands

Macrocyclic Lewis acidic hosts with structures incorporating electron-withdrawing icosahedral carboranes and electrophilic mercury centers bind a variety of electron-rich guests. These compounds, the so-called mercuracarborands, are synthesized by a kinetic halide ion template effect that affords tetrameric cycles or in the absence of halide ion templates, cyclic trimers. Both types of mercuracarborands form stable host–guest complexes with anionic and neutral electron-rich molecules. The multidentate structure of mercuracarborand hosts has made these unique molecules ideal for catalytic and ion-sensing applications as well as for the assembly of supramolecular architectures.     

Selenium containing macrocycles:transformation between Se-N/Se-S/Se-Se bonds

Macrocycles possess potential applications in supramolecular chemistry and biosystems.Thus development of new kinds of macrocycles is of significance.Herein,novel macrocycles containing Se-Se/Se-S bonds were synthesized via transformation between selenium related dynamic covalent bonds.A monomer containing two ebselen moieties was synthesized(M1).The Se-N bonds in M1 were reduced by dithiothreitol,forming Se-S linked dimer(D1).To realize the transformation from Se-S bonds to Se-Se bonds,guest molecules were added as template,triggering the formation of Se-Se linked dimer(D2).The formation of these two new kinds of macrocycles was determined by ~1H NMR and ~(77)Se NMR,and the necessity of guest molecules was also confirmed.The introduction of ebselen moieties and Se-S bonds or Se-Se bonds into macrocycles may endow it with new responsiveness and bioactivities,as well as new types of host-guest chemistry.     

Effects of the composition of the reaction mixture and the nature of the template on the structure of mesoporous aluminosilicates formed in the presence of lecithin

It has been established that supramolecular structures of lecithin can act as templates in the synthesis of mesoporous aluminosilicates. Mesoporous substances, with pore dimensions up to 100 Å and biporous materials can be obtained when various combinations of lecithin with cetyltrimethylammonium bromide or octadecylamine are used as template agents in the aluminosilicate system.     

磁性离子印迹技术用于元素形态分离分析

元素的形态决定了其在环境和生物过程中的不同行为,形态分析正在被分析化学、环境化学、地球化学、生态学、农学和生物医学等众多学科所关注。环境和生物样品基质复杂、化学形态多样、含量低且易转化是元素形态分析面临的挑战,因此对元素形态的甄别、定量、生态毒性评价和生理功能研究需要对原生形态进行高选择性识别和高效率分离。固相萃取是一种有效应对以上难题的方法,但现有材料和方法远不能满足要求。离子印迹聚合物可与印迹金属离子特异性结合,具有准确、灵敏、可靠的特点,近年来在元素形态分离富集和分析检测方面得到了较为广泛的应用。鉴于非磁性吸附剂在固相萃取操作时,需要将分散在样品溶液中的吸附材料经过离心或过滤分离,操作比较繁琐费时,而磁性材料易被外部磁场快速分离,因此操作简便快速的磁固相萃取正成为元素形态分离富集中一种极具潜力的方法。这篇综述系统总结了离子印迹技术的最新进展,包括离子印迹技术的原理、离子印迹聚合物的制备方法,并根据元素形态分析中离子印迹磁固相萃取的发展现状,分析了离子印迹技术所面临的挑战,最后对元素形态分析中离子印迹技术的未来发展方向和策略提出了建议,提出开发基于有机-无机杂化聚合的多功能磁性离子印迹纳米复合物用于样品的前处理是建立识别选择性高、分离能力强、吸附容量大、形态稳定性好的形态分析方法的一种重要举措。     

Strategies for the construction of supramolecular assemblies from poly-NHC ligand precursors

The field of supramolecular assemblies has developed rapidly in the last few decades, thanks in a large part to their diverse applications. These assemblies have been mostly based on Werner-type coordination motifs in which metal centres are coordinated by nitrogen or oxygen donors. Recently, N-heterocyclic carbene(NHC) ligands have been employed as carbon donors not only because of their appealing structures but also due to the extensive applications in catalysis, biomedicine and material science of the resulting assemblies. During the last decade, NHC-based supramolecular assemblies have witnessed rapid growth and extensive application in molecular recognition, luminescent materials and catalysis. For different topological systems, a diverse selection of poly-NHC precursors and synthetic strategies is crucial to precisely control the synthesis of supramolecular architectures. Several synthetic strategies have been developed to synthesise two-dimensional(2D) molecular metallacycles and three-dimensional(3D) metallacages from a wide range of poly-NHC precursors, including a straightforward one-pot strategy,supramolecular transmetalation, stepwise synthesis, an improved one-pot strategy involving self-sorting behaviour of 3D metallacages and a subtle variation strategy of poly-NHC ligand precursors. This review offers a summary of the synthetic strategies applied for the construction of different poly-NHC-based supramolecular assemblies, particularly emphasizes recent progress in the synthesis of large and complex supramolecular assemblies from poly-NHC precursors, and further attention is given to their application in postsynthetic modifications(PSMs), host-guest chemistry, luminescent properties and biomedical applications.     

Resorcinarenes as templates

Metal ions are superb at templating the synthesis of small macrocycles that are decorated with Lewis basic sites. However, for the synthesis of larger macrocycles, or the synthesis of macrocycles devoid of an array of Lewis basic sites, metal ions are less useful. Here we demonstrate that resorcinarenes can be used as templates to engender the efficient formation of large crown ethers. A three step process of 1). tethering moieties to the template, 2). linking those moieties, and 3). then cleaving off the template leads to the efficient formation of a family of aromatic crown ethers. If adaptable, this approach will prove useful for the construction of macrocycles that are hard to obtain from a step-wise synthesis.     

Vom einfachen Komplex zum komplexen Gitter: Metallo‐supramolekulare Chemie

Supramolecular structures and metal‐complexes play a dominant role in the functionality of biomolecules. Taking nature as an example a major goal of metallo‐supramolecular chemistry is the extension of the traditional coordination chemistry towards supramolecular architectures, utilizing complex ligand systems. Herein we describe a wide range of different geometries such as helicates, linear rod‐like polymers, ladders, racks or grids, which are realized by the combination of supramolecular ligands and coordinating metal ions on the basis of self‐assembly and self‐recognition processes. Besides the pure beauty of the structures, the electro‐, photochemical and magnetic properties of the materials might open avenues to applications as smart coatings, catalysts or optical devices.     

Structural Transformation and Stabilization of Metal–Organic Motifs Induced by Halogen Doping

The structural transformation of supramolecular nanostructures with constitutional diversity and adaptability by dynamic coordination chemistry would be of fundamental importance for potential applications in molecular switching devices. The role of halogen doping in the formation of elementary metal–organic motifs on surfaces has not been reported. Now, the 9‐ethylguanine molecule (G) and Ni atom, as a model system, are used for the structural transformation and stabilization of metal–organic motifs induced by iodine doping on Au(111). The iodine atoms are homogeneously located at particular hydrogen‐rich locations enclosed by G molecules by electrostatic interactions, which would be the key for such an unexpected stabilizing effect. The generality and robustness of this approach are demonstrated in different metal–organic systems (G/Fe) and also by chlorine and bromine.     

Templat-Reaktionen II. Herstellung von tricyclischen und tetracyclischen Metallkomplexen aus aliphatischen Diaminen und Phenylazo-malondialdehyd-Derivaten

Template-Reactions II. Syntheses of tricyclic and tetracyclic metal complexes from aliphatic diamines and phenylazo-malondialdehyde-derivatives A template synthesis of metal complexes with 14- and 16-membered macrocycles 6 resp. 10 has been devised. These compounds are obtained in high yield by the condensation of aliphatic 1,2-or 1,3-diamines with phenylazo-malon-dialdehydes in the presence of divalent metal ions such as Cu(II) and Ni(II). This is the first reported one-step synthesis of tetraaza-annulenes with aliphatic diamines. The formation of the intermediate tricyclic complexes 5 and 9, obtained either by a template or a nontemplate synthesis, is also described. Ring closure with diamines leads again to 6 and 10 or to asymmetric tetraaza-macrocyclic systems such as 7 or 11.     

Combining Imine Condensation Chemistry with [3,3] Diaza-Cope Rearrangement for One-Step Formation of Hydrolytically Stable Chiral Architectures

Dynamic covalent chemistry (DCC) has, in recent years, provided valuable tools to synthesize molecular architectures of increasing complexity. We have also taken advantage of imine DCC chemistry to prepare TPMA -based supramolecular cages for molecular recognition applications. However, the versatility of this approach has as a major drawback the intrinsic hydrolytic lability of imines, which hampers some applications. We present herein a synthetic strategy that combines the advantages of a thermodynamic-driven formation of a supramolecular structure using imine chemistry, together with the possibility to synthetize chiral hydrolytically stable structures through a [3,3]-sigmatropic rearrangement. A preliminary mechanistic analysis of this one-pot synthesis and the scope of the reaction are also discussed.     

Endo- and exotemplating to create high-surface-area inorganic materials

Porous and high-surface-area materials are of interest to many scientific communities. Templating pathways can be used to synthesize such materials with a high degree of control over their structural and textural properties. As templates molecular or supramolecular units are added to the synthesis mixture. They are occluded in the growing solid and leave a pore system after their removal. For such templates the term "endotemplate" is introduced. Alternatively, the templates can be materials with structural pores in which another solid is created, thus providing a scaffold for the synthesis. After removal of the scaffold, a porous or finely divided solid remains, depending on the connectivity of the template. Such a template is termed an "exotemplate". By judicious choice of the templating procedure, unprecedented control of the structure and texture on length scales between nanometers and micrometers has been achieved over the last few years.     

3D Supramolecular Network Based on Hydrogen Bonds Between 1D [ Ni(μ2 -C2O4 ) (Him) 2 ] Zigzag Chains

Introduction In recent years, considerable attention has been paid to supramolecular networks based on metal organic building blocks because of their potential applications in diverse fields, such as, catalysis, optics, sensors,magnetism, and molecular recognition[1-3]. On the basis of the principles of crystal engineering and special synthesis strategies, several novel supramolecular frameworks have been assembled from various organic,inorganic and metal-organic moieties, which largely enriches the structure chemistry of solid state materials[4-9].