Bending Nanofibers into Nanospirals: Coordination Chemistry as a Tool for Shaping Hydrophobic Assemblies

In the current work, we demonstrate how coordination chemistry can be employed to direct self‐assembly based on strong hydrophobic interactions. To investigate the influence of coordination sphere geometry on aqueous self‐assembly, we synthesized complexes of the amphiphilic perylene diimide terpyridine ligand with the first‐row transition‐metal centers (zinc, cobalt, and nickel). In aqueous medium, aggregation of these complexes is induced by hydrophobic interactions between the ligands. However, the final shapes of the resulting assemblies depend on the preferred geometry of the coordination spheres typical for the particular metal center. The self‐assembly process was characterized by UV/Vis spectroscopy, zeta potential measurements, and cryogenic transmission electron microscopy (cryo‐TEM). Coordination of zinc(II) and cobalt(II) leads to the formation of unique nanospiral assemblies, whereas complexation of nickel(II) leads to the formation of straight nanofibers. Notably, coordination bonds are utilized not as connectors between elementary building blocks, but as directing interactions, enabling control over supramolecular geometry.     

Coordination chemistry of N-tetraalkylated cyclam ligands—A status report

N-alkylation of macrocyclic amines has a significant impact on their properties as ligands for metal ions. This article examines the development of the coordination chemistry of N-alkylated cyclam ligands from its inception in 1973 with the first report of tetramethylcyclam. Emphasis is on: (1) the stereochemistry of metal complexation, including the effects of inclusion of functional groups in one or two of the N-alkyl groups; (2) the effect of N-alkylation on the metal–donor interaction; (3) the ability of tertiary amine ligands to stabilize complexes of metal ions in unusual oxidation states.     

Merging porphyrins with organometallics: synthesis and applications

The coordination chemistry of porphyrins has traditionally involved the ability of the porphyrin's tetrapyrrolic core to accommodate metal ions of varying charges and sizes, and on the organometallic chemistry of the resulting metalloporphyrins. However, the organometallic chemistry of porphyrins is not necessarily restricted to the metal bound in the porphyrin core, but can also be extended to the porphyrin periphery, be it through direct metalation of the porphyrin macrocycle at the meso or beta position, or by attachment to or merger of the porphyrin skeleton with ligands, followed by metalation. This Review focuses on the synthetic strategies used for porphyrins with peripheral metal-carbon bonds. The exciting results that have been produced underscore the importance and future potential of this field.     

Ligand design for multidimensional magnetic materials: a metallosupramolecular perspective

The aim and scope of this review is to show the general validity of the 'complex-as-ligand' approach for the rational design of metallosupramolecular assemblies of increasing structural and magnetic complexity. This is illustrated herein on the basis of our recent studies on oxamato complexes with transition metal ions looking for the limits of the research avenue opened by Kahn's pioneering research twenty years ago. The use as building blocks of mono-, di- and trinuclear metal complexes with a novel family of aromatic polyoxamato ligands allowed us to move further in the coordination chemistry-based approach to high-nuclearity coordination compounds and high-dimensionality coordination polymers. In order to do so, we have taken advantage of the new developments of metallosupramolecular chemistry and in particular, of the molecular-programmed self-assembly methods that exploit the coordination preferences of metal ions and specifically tailored ligands. The judicious choice of the oxamato metal building block (substitution pattern and steric requirements of the bridging ligand, as well as the electronic configuration and magnetic anisotropy of the metal ion) allowed us to control the overall structure and magnetic properties of the final multidimensional nD products (n = 0-3). These species exhibit interesting magnetic properties which are brand-new targets in the field of molecular magnetism, such as single-molecule or single-chain magnets, and the well-known class of molecule-based magnets. This unique family of molecule-based magnetic materials expands on the reported examples of nD species with cyanide and related oxalato and dithiooxalato analogues. Moreover, the development of new oxamato metal building blocks with potential photo or redox activity at the aromatic ligand counterpart will provide us with addressable, multifunctional molecular materials for future applications in molecular electronics and nanotechnology.     

Supramolecular coordination chemistry of aromatic polyoxalamide ligands: A metallosupramolecular approach toward functional magnetic materials

The impressive potential of the metallosupramolecular approach in designing new functional magnetic materials constitutes a great scientific challenge for the chemical research community that requires an interdisciplinary collaboration. New fundamental concepts and future applications in nanoscience and nanotechnology will emerge from the study of magnetism as a supramolecular function in metallosupramolecular chemistry. Our recent work on the rich supramolecular coordination chemistry of a novel family of aromatic polyoxalamide (APOXA) ligands with first-row transition metal ions has allowed us to move one step further in the rational design of metallosupramolecular assemblies of increasing structural and magnetic complexity. Thus, we have taken advantage of the new developments of metallosupramolecular chemistry and, in particular, the molecular-programmed self-assembly methods that exploit the coordination preferences of paramagnetic metal ions and suitable designed polytopic ligands. The resulting self-assembled di- and trinuclear metallacyclic complexes with APOXA ligands, either metallacyclophanes or metallacryptands, are indeed ideal model systems for the study of the electron exchange mechanism between paramagnetic metal centers through extended π-conjugated aromatic bridges. So, the influence of different factors such as the topology and conformation of the bridging ligand or the electronic configuration and magnetic anisotropy of the metal ion have been investigated in a systematic way. These oligonuclear metallacyclic complexes can be important in the development of a new class of molecular magnetic devices, such as molecular magnetic wires (MMWs) and switches (MMSs), which are major goals in the field of molecular electronics and spintronics. On the other hand, because of their metal binding capacity through the outer carbonyl-oxygen atoms of the oxamato groups, they can further be used as ligands, referred to as metal–organic ligands (MOLs), toward either coordinatively unsaturated metal complexes or fully solvated metal ions. This well-known “complex-as-ligand” approach affords a wide variety of high-nuclearity metal–organic clusters (MOCs) and high-dimensionality metal–organic polymers (MOPs). The judicious choice of the oligonuclear MOL, ranging from mono- to di- and trinuclear species, has allowed us to control the overall structure and magnetic properties of the final oxamato-bridged multidimensional (nD, n = 0–3) MOCs and MOPs. The intercrossing between short- (nanoscopic) and long-range (macroscopic) magnetic behavior has been investigated in this unique family of oxamato-bridged metallosupramolecular magnetic materials expanding the examples of low-dimensional, single-molecule (SMMs) and single-chain (SCMs) magnets and high-dimensional, open-framework magnets (OFMs), which are brand-new targets in the field of molecular magnetism and materials science.     

Diol-type ligands as central 'players' in the chemistry of high-spin molecules and single-molecule magnets

The combination of diol-type ligands with paramagnetic transition metal ions has led to the isolation of a host of new homometallic and heterometallic clusters, high-spin molecules and single molecule magnets ranging in nuclearity from two to forty four and with spin ground states as large as S = 61/2. The ligands, whose cluster coordination chemistry is discussed in this article, are 1,3-propanediol and its derivatives, diethanolamine and its derivatives, pyridine-2,6-dimethanol and the gem-diol form of di-2-pyridyl ketone. The structural diversity of the complexes stems from the ability of the ligands to adopt a variety of bridging coordination modes depending on the positions of the two hydroxyl groups in the molecule, the presence/absence of extra donor groups and on the reaction conditions. Examples of 'true' reactivity chemistry involving clusters of diol-type ligands are also given. The activation of pyridine-2,6-dimethanol and di-2-pyridyl ketone by 3d-metal centres towards further reactions seems to be an emergent area of synthetic chemistry.     

Koordinationspolymere aus Metallotripyrrinen

Coordination Polymers from Metal Tripyrrins This Research Report summarizes recent advances in the coordination chemistry of tripyrrins and related ligands with a special emphasis on the structural chemistry of coordination polymers with such ligands. The tripyrrin ligand is unique in supporting the formation of 1D‐ and 3D supramolecular structures from pentacoordinate transition metal ions due to an effective blockage of their sixths coordination site. Linear coordination polymers have been observed with a multitude of bidentate and tridentate bridging ligands like trifluoroacetate, azide, thio‐ and selenocyanate, and higher order pseudohalides. Homo‐ and heterodimetallic species have been obtained by the use of cyanometallates and could be characterized structurally in two cases. Besides the covalent coordination bonds several secondary interactions like hydrogen bonding and π‐stacking were found to support these coordination polymers and are demonstrated to allow the preparation of species with functionalized inner surfaces.     

Synthesis, structure and spectroscopy of new thiopyrone and hydroxypyridinethione transition-metal complexes

The coordination chemistry of several O,S mixed donor ligands, namely thiopyrone and hydroxypyridinethione chelators, with a variety of middle and late first-row transition-metal ions is described. Complexes of 3-hydroxy-2-methyl-4-thiopyrone (thiomaltol) with cobalt(II), copper(II) and zinc(II); 3-hydroxy-1,2-dimethyl-4(1H)-pyridinethione (3,4-HOPTO) with iron(III), nickel(II), copper(II) and zinc(II); and 3-hydroxy-1-methyl-2(1H)-pyridinethione (3,2-HOPTO) with iron(III), nickel(II), copper(II) and zinc(II) have been synthesized and characterized. The structures, absorbance spectroscopy, cyclic voltammetry and superconducting quantum interferometer device (SQUID) measurements of selected metal complexes, as well as ligand protonation constants, are reported. Most of the metal complexes show coordination geometries indicative of a strong trans influence by the O,S chelators. The data presented herein provide the most detailed study of the transition-metal coordination chemistry of both thiopyrone and hydroxypyridinethione O,S donor ligands to date, and provide the basis for the investigation of these ligands in realm of biological inorganic chemistry.     

Interactions between metal ions and carbohydrates. Coordination behavior of neutral erythritol to Ca(II) and lanthanide ions

The study of the sugar-metal ion interactions remains one of the main objectives of carbohydrate coordination chemistry because the interactions between metal ions and carbohydrates are involved in many biochemical processes. This paper presents a comparison of coordination structures of erythritol with alkaline-earth-metal and lanthanide chloride and nitrate in the solid state using FT-IR and X-ray diffraction. Neutral, nondeprotonated erythritol (E) reacts with CaCl(2) to give three CaCl(2)(-)erythritol (CaE(I), CaE(II), CaE(III)) complexes, showing that three of the five general features of calcium-carbohydrate complexes deduced in the reference encounter contrary examples. Different coordination structures have been observed for calcium and lanthanide chloride and nitrates. The coordination of carbohydrates to metal ions is complicated, and erythritol, chloride ions, nitrates, water molecules, and ethanol (crystallization medium and reaction solvents) have the chance to coordinate to metal ions. IR spectral results show that different lanthanide ions, from LaCl(3) to TbCl(3), have similar coordination structures with erythritol. The results show that erythritol can act as two bidentate neutral ligands (CaE(I), CaE(II), CaE(III), CaEN, PrE, NdE) or as a three-hydroxyl donor (NdEN). The IR results are consistent with the crystal structures.     

Open shell organometallics: a general analysis of their electronic structure and reactivity

Transition metal organometallic compounds that contain fewer than 18-electrons and two or more unpaired electrons are generally excluded from treatises of either Werner-type coordination compounds or organometallic chemistry. However, they can be seen as the bridge filling the gap between these two traditional areas of coordination chemistry. Their magnetic and optical properties are reminiscent of the Werner-type complexes, whereas their chemical reactivity parallels that of the lower-valent organometallics. Spin state change phenomena are of paramount importance in this area. This paper provides a broad perspective of this area, with particular attention to: (i) how the ground state properties can be related to the metal and ligands nature; (ii) under which circumstances the often inappropriately invoked concept of “spin block” is meaningful; (iii) the spin acceleration concept; (iv) how the coordination sphere affects the topology of the reaction coordinate in the vicinity of spin crossing points; and (v) the effect of spin state changes on reaction selectivities.     

The Coordination Chemistry and Organometallic Chemistry of Tridentate Oxygen Ligands with π-Donor Properties

Metal complexes are capable of accomplishing almost anything, provided they contain the proper metal/ligand combinations. A host of essential biochemical transformations—but also a great many industrially significant reactions—occur within the coordination spheres of metal ions. For instance, the particular arrangement of ligands in the zinc-containing enzyme carboanhydrase is responsible for an acceleration in the hydration of CO₂ by a factor of 10⁹. It is the ligands that determine whether an iron atom will transfer molecular oxygen, as in the case of hemoglobin, or electrons, as with the cytochromes. By varying the ligands it is possible to establish in advance whether a metal ion in the presence of synthesis gas will cause an olefin to be hydrogenated or hydroformylated. Stated more generally, it is the ligands that stabilize the particular oxidation states of a metal and determine how substrate molecules will be coordinated and undergo reaction. The synthesis of new ligands that confer specific reactivity on metal ions is thus an important challenge for the coordination chemist. The following article describes organometallic compounds of the type [CpCo{P(O)R′R″}₃]^?, which have developed from an extremely unreactive laboratory curiosity into versatile oxygen-containing ligands whose steric and electronic properties promise a series of interesting applications.     

Synthesis, coordination properties, and analytical applications of mixed donor macrocycles containing the 1,10-phenanthroline sub-unit

The coordination properties towards different metal ions of a new class of mixed N/S-, and N/S/O-donor macrocycles containing the 1,10-phenanthroline sub-unit in the cyclic framework are reviewed. The conformational constraints imposed by the heteroaromatic fragment onto the aliphatic portion of the ring determine the coordination mode of these ligands which can stabilise low-valent Ni⁺, Pd⁺, Pt⁺, and Rh⁺ metal complexes. Structural and thermodynamic aspects of the coordination chemistry of these ligands are considered together with possible applications as building blocks in the synthesis of multi-centred systems, and as template in the construction of extended polyiodide networks. However, solution studies demonstrate the inability of these ligands to work as selective and specific fluorescent chemosensors for heavy transition and post-transition metal ions and the formation constants evaluated for the formation of 1:1 complexes with Pb²⁺, Cd²⁺, Hg²⁺, Cu²⁺, and Ag⁺ in acetonitrile are of the same order of magnitude. Nevertheless, some of these macrocyles are extremely effective to recognise Cu²⁺ or Ag⁺ over the other metal ions in transport processes, and have been successfully used as neutral ionophore in the construction of PVC-based ionselective electrodes and supported liquid membranes for analytical detection and separation, respectively, of these metal ions.     

胆红素及其两亲衍生物的Langmuir-Blodgett膜研究

研究了亚相酸度和金属离子对胆红素(1)及其两个两亲衍生物胆红素二(十八烷基)酯(2)和胆红素二(十八烷基)酰胺(3)的单分子膜和LB膜性能的影响.通过π-A等温线、X射线光电子能谱、紫外-可见光谱等方法,研究了它们在有序分子膜中的分子伸展及与金属离子的配位方式.胆红素及其两亲衍生物与金属离子在有序分子膜中的配位(生成1:1型配合物)明显不同于其在本体溶液中的配位(1:1,1:2或2:1型配合物).小角X射线衍射表明1,2和3形成双层膜间距分别为2.15,5.55和5.65nm的Y型LB膜.     

Phosphonates,their complexes and bio-applications: A spectrum of surprising diversity

This review provides a summary of the coordination chemistry of mono-, bis- and polyphosphonates, as well as of their functionalized analogues. Specific interactions with various metal ions will be discussed in the context of their biological, biomedical and nanotechnological applications. Several complexes will be shown to reveal a spectacular spectrum of possibilities, which the phosphonate moiety gives to coordination chemistry.We would like to show a link between coordination properties and unique functionality of particular phosphonate complexes which were developed and successfully applied in different branches of biological science.     

Ligands with Two Monoanionic N,N-Binding Sites: Synthesis and Coordination Chemistry

Polytopic ligands have become ubiquitous in coordination chemistry because they grant access to a variety of mono- and polynuclear complexes of transition metals as well as rare-earth and main-group elements. Nitrogen-based ditopic ligands, in which two monoanionic N,N-binding sites are framed within one molecule, are of particular importance and are therefore the primary focus of this review. In detail, bis(amidine)s, bis(guanidine)s, bis(β-diimine)s, bis(aminotroponimine)s, bis(pyrrolimine)s, and miscellaneous bis(N,N-chelating) ligands are reviewed. In addition to the general synthetic protocols, the application of these ligands is discussed along with their coordination chemistry, the multifarious binding modes, and the ability of these ligands to bridge two (or more) metal(loids).     

A survey of crystal structures and biological activities of platinum group metal complexes containing N-acylthiourea ligands

Abstract

N-Acyl-thioureas are important compounds in the field of organic synthesis and medicinal chemistry. Research interest in these compounds has grown recently because coordination to metal ions enhances their application especially in view of medicinal studies. These thiourea derivatives possess rich coordination chemistry and the coordination behavior of these derivatives alters upon reaction with different metals. Such ligands generally coordinate to Pt(II) and Pd(II) ions in a bidentate S,O manner and often coordinate to Ru(II), Rh(III) and Ir(III) centers through the S donor atom. We isolated some complexes of these ligands by reaction with sodium azide which coordinates to Ru(II), Rh(III), and Ir(III) in a bidentate S,N fashion. The deprotonated thiourea nitrogen atom resulted in the formation of strained 4-membered ring structures around the metal center. Biological application of N-acyl thiourea derivatives and their platinum group metal complexes are further discussed. Studies has shown that these compounds can be used as drugs to treat several human diseases like microbial infections, tuberculosis, carcinomas, malaria, leishmaniasis, urease inhibitors and anti-inflammatory. This review intends to summarize the recent advancement in the chemistry of N-acyl-thioureas and highlight some perspectives in the synthesis, versatile coordination behavior to ruthenium, rhodium, iridium, platinum and palladium, and their metal complexes in biological applications.     

氮杂环配体自组装螺旋链状结构配位聚合物的研究进展

螺旋结构配位聚合物在光学装置、生物模拟化学、非对称催化化学、手性识别、生物结构等多学科领域的应用,引起了人们极大的兴趣。本文综述了氮杂环配体自组装螺旋结构配位聚合物的最新进展,按照咪唑、三唑、吡啶、嘧啶及其衍生物配体分类总结了它们构建螺旋配位聚合物的结构,并简述了通过自发手性识别过程得到纯手性螺旋配位聚合物的影响因素,展望了具有螺旋链状配位聚合物的发展前景以及其开发应用潜能。     

The coordination chemistry of 1,2,4,5-tetrazines

1,2,4,5-Tetrazine and its 3,6-disubstituted derivatives exhibit a particular coordination chemistry, characterized by electron and charge transfer phenomena and by the ability of these heteroatom-rich ligands to bridge metal centers in various ways. A very low-lying π* orbital localized at the four nitrogen atoms is responsible for intense low-energy charge transfer absorptions, electrical conductivity of coordination polymers, unusual stability of paramagnetic radical or mixed-valent intermediates and for often well-resolved EPR hyperfine structure in the radical complexes. Substituted 1,4-dihydro-1,2,4,5-tetrazines have also been used as bridging ligands. The structural consequences of electron transfer as well as the capability for efficient and variable metal–metal bridging render the tetrazines as valuable components of supramolecular materials.     

Fifty Years of Inorganic Biomimetic Chemistry: From the Complexation of Single Metal Cations to Polynuclear Metal Complexes by Multidentate Thiolate Ligands

This article covers 50 years of coordination chemistry of transition metal complexes and metal-sulfur aggregates involving thiolate-incorporating ligands by reviewing selected examples. The studies in the coordination chemistry of sulfur-rich ligands have been undoubtedly triggered and fed by the concomitant development of bioinorganic chemistry, particularly of iron-sulfur enzymes. The review is broken down in five sections, which examine complexes of increasing nuclearity, including binuclear complexes based on compartmental macrocyclic ligands. We show also how ligand engineering has allowed the researchers in the field to control the nuclearity of the complexes, which was a particularly difficult task for sulfur-based ligands, as thiolates show a strong tendency to coordinate to more than one metal cation at once.     

Synthesis of oligopyridines and their metal complexes as precursors to topological stereoisomers

[structure: see text]. Palladium-based carbon-carbon coupling reactions in sequence with halogen-exchange chemistry on a series of heterocycles lead to an efficient synthetic strategy for oligopyridines that bind metal ions such as ruthenium to form coordination racks. The particular structures are designed to form terpyridine subunits for octahedral binding. Reaction of 4,6-diiodopyrimidine produces a "double-bay" terpyridine from which binuclear coordination complexes have been formed.