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Self‐Assembly, Structure and Solution Dynamics of Tetranuclear Zn2+ Hydrazone [2×2] Grid‐Type Complexes
European Journal of Inorganic Chemistry
Abstract
We describe the self-assembly processes as well as the structural
and physico-chemical properties of [2×2]Zn2+4 grid complexes involving the bis-tridentate ligands 7–12, basedon bis(hydrazone)pyrimidine complexation subunits and octahedrally
coordinated Zn2+ ions. The NMR spectroscopic
data and the X-ray crystal structure results indicate that in
solution and in the solid state the complexes 13–18 adopt a
very compact arrangement providing stable [2×2] hydrazone-
grid arrays. The π–π stacking between the phenyl ring
and the hydrazone units of the perpendicular ligands in the
complexes induces a perfect orthogonal arrangement suitable
for applications in self-organized metallosupramolecular
systems. Zinc complexes provide an opportunity to studythe acid–base chemistry without the added effects due to paramagnetism or redox chemistry. The intermediate protonated
grids undergo relatively rapid proton exchange on the
NMR timescale, the presence of a sharp pyrimidine proton
resonance suggesting that there is significant delocalization
of the negative charge along the backbone of the ligand. Rotation
of the phenyl ring is observed. It involves probably a
mechanism in which one of the ligands partially dissociates
allowing the initially intercalated phenyl group to rotate, before
recoordination of the terminal pyridine.
... The prototypical ligands of this type may be described as py 1 -py 2 -pym-py 2py 1 species, where py 1 ϭ 2-substituted pyridine, py 2 ϭ 2,6disubstituted pyridine and pym ϭ 4,6-disubstituted pyrimidine [3]. Replacement of py 2 by an isomorphic equivalent, e.g. the hydrazone group (hyz) [4], greatly facilitates the synthesis of such ligands and has the added advantage that the ϭN-N(R)unit (R ϭ H, alkyl) of the hydrazone may be deprotonated when R ϭ H [6], enhancing the range and allowing modulation of the electronic properties accessible beyond those provided by simple variation of R [7]. ...
... Ligands 1 and 2H 2 [5,7], Pb(OTf) 2 [23] and [Hg(CH 3 SOCH 3 ) 6 ]-(OTf) 2 [24] were prepared as previously described. The following reagents were purchased from commercial sources: Hg(OTf) 2 (Aldrich), CD 3 CN (Eurisotop). ...
... Ligands 1 pyridine-2-carboxaldehyde[2-phenyl-pyrimidine-4,6-diyl]bis(methylhydrazone)[5,7] and 2H 2 pyridine-2-carboxaldehyde[2-phenyl-pyrimidine-4,6-diyl]bis(hydrazone)[7] were obtained by the reaction of the corresponding bis(hydrazino)pyrimidine with 2 equivalents of pyridine-2-carboxaldehyde (Fig. 1)in ethanol, at reflux or at room temperature. ...
Solution and solid state studies of the complexation of Hg2+ and Pb2+ by the homologous bis-tridentate ligands 1 and 2H2 obtained by condensation of bis(methylhydrazino)phenylpyrimidine and bis(hydrazino)phenylpyrimidine, respectively, with pyridine-2-carboxaldehyde, have provided evidence for the formation of both grid and rack species. With Hg2+, there is little indication for other than grid species, the grid complex [Hg4(2H2)4](CF3SO3)8 being characterised crystallographically. With Pb2+, the only crystalline species readily isolated are rack complexes of the ligands 1 and 2H2.
... It may be achieved by condensation of a central pyrimidine-4,6-dicarbaldehyde with either a pyridine-2-hydrazine or a hydrazide (Figure 1, routes leading to products A and B, respectively), thus generating ditopic ligands incorporating two hydrazone functions as central groups of two tridentate metal coordination centres. Ligands containing two unsubstituted hydrazone units (Figure 1) possess two ionisable sites [12, [14][15][16][17][18][19] that may serve to modulate (i) the coordination properties of the ligands, (ii) the optical electronic and magnetic properties of the grid complexes, as well as (iii) the communication between external effectors and the metal centres. ...
... (Elemental analysis of the dried bulk material is consistent with a formulation in which only one molecule of nitromethane of solvation is present.) The cation present in the lattice ( Figure 8) is a 2ϫ2 grid species of a form very similar to those formed with neutral hydrazone ligands [8,18,33] and remarkably similar to grids formed by the deprotonated acylhydrazones described below. It is thus a useful reference point for the whole of the present discussion. ...
... The compound was recrystallised from hot thf by addition of an equal volume of diethyl ether after cooling. C 18 Co II Complex (Co/L 1:1) of the Doubly Deprotonated Ligand: The procedure above was repeated except that the quantity of triethylamine added (20 mg) was doubled. Here, copious precipitation of a dark red solid occurred immediately, though again 12 h was allowed for equilibration. ...
Ditopic bis(acylhydrazone) ligands, derived from the reactions of carbohydrazides with 2-phenylpyrimidine-4,6-dicarbaldehyde and designed for grid formation with octahedrally coordinating transition-metal ions, exhibit a varied coordination chemistry depending upon the degree of their deprotonation. The neutral acylhydrazones are relatively poor ligands and are seemingly involved in multiple, labile complexation equilibria varying with the solvent and the particular metal salt in solution; nevertheless, grid complexes of different forms can be isolated in the solid state. Although only limited study has been made of the singly deprotonated ligands, grid species appear to be much more readily isolated. With the doubly deprotonated ligands, grid formation is strongly favoured in both the solution and solid states. As a consequence, the grid structures form spontaneously in the presence of a base by self-assembly from their components without need to preform the ditopic ligands. Extensive structural studies have been carried out both to establish the grid structures and to analyse the nature of the supramolecular interactions possible for neutral and charged grid species. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
... In this work, we approached a synthetic methodology using Zn(BF 4 ) 2 as the source for the metal cation. Zn 2+ is a well-known cation in the construction of supramolecular grid-complexes thanks to its diamagnetic behavior, which allows the characterization of its complexes by NMR spectroscopy (Barboiu, et al., 2006). Furthermore, different anions have shown a templating effect on the formation of certain supramolecular structures (Hasenknopf, et al., 1997). ...
... Phenyl substituents in the position 2 of the pyrimidine ring are amongst the most used in the construction of grid complexes. Their presence allow several π-π interactions that stabilize the structure (Dutta, et al., 2011) The amount of information related in the bidimensional experiments agreed with other grid complexes reported in the literature (Barboiu, et al., 2006;Stefankiewicz, et al., 2010), which allowed us to confirm that our complex exhibited a grid structure in solution as shown in Figure S10, https://www.raccefyn.co/index.php/raccefyn/article/ downloadSuppFile/822/3891; in which the phenyl group The UV-Vis spectrum of the metal grid complex and the organic ligand 3 were taken using methanol as solvent. ...
Una nueva bis(hidrazona), altamente soluble en solventes orgánicos comunes, se sintetizó y caracterizó mediante diversas técnicas espectroscópicas. El compuesto se utilizó como ligando ditópico en la construcción de estructuras supramoleculares de tipo rejilla (rejillas supramoleculares o complejos metálicos de tipo rejilla) utilizando Zn2+ como catión metálico. El complejo supramolecular se confirmó mediante resonancia magnética nuclear RMN-1H y bidimensional. El arreglo de tipo rejilla se determinó mediante las señales de RMN-1H del anillo fenilo del ligando orgánico que cambia su velocidad de rotación y, por ende, su ambiente químico al coordinarse en dicho arreglo. Por último, se realizaron estudios de UV-Vis y voltamperometría cíclica y de onda cuadrada, con el fin de determinar las propiedades optoelectrónicas y electroquímicas de estos compuestos. Tanto la bis(hidrazona) como el complejo de tipo rejilla aquí presentados, exhiben varios potenciales de oxidación-reducción, los cuales se estudiaron en detalle mediante las técnicas mencionadas y cuyo estudio sirve de base para el desarrollo futuro de estructuras supramoleculares que puedan utilizarse como interruptores moleculares electroquímicos. © 2019. Acad. Colomb. Cienc. Ex. Fis. Nat.
The sequential assembly of first terminally functionalized bishydrazone ligands followed by their coordination with Zn( ii ) metal cations yields peripherally multi-functionalized [2 × 2] grid-type complexes.
Without a templated mechanism, a new corner-like complex ([Fe(C25H32N8S)2]²⁺=[Fe]) and a new grid-like one ([Fe4(C23H28N8S)4]⁸⁺=[Fe4]) were obtained from the self-assembly of two structurally related bis(hydrazones) (C25H32N8S=1; C23H28N8S=2) with Fe(II) under identical reaction conditions, commonly employed for the efficient synthesis of grid-like complexes. The electrochemical and magnetic properties of these complexes were studied. Both complexes undergo a Fe(II)/Fe(I) reduction process in each of their metal centers, but only the grid-like complex exhibits easily oxidizable metal centers. In the solid state, both complexes are in the low spin state within a wide range of temperatures, but the corner has several types of high spin states coexisting at all times. From an exploratory viewpoint, our results are important to carry out the eventual synthesis of metal complexes with suitable properties for nanotechnological applications.
There is great interest in metallosupramolecular materials because of their use in magnetic, photonic and electronic materials. Functional Metallosupramolecular Materials focuses on the applications of these materials covering the chemistry underlying the synthesis of a variety of ligands to coordinate various metal ions and the generation of 2D and 3D materials based on these constructs.
The book starts by looking at different metallosupramolecular systems including naturally occurring functional metallosupramolecular materials; DNA-based metallosupramolecular materials; metallopolymers; metallogels as well as functional materials based on MOFs. Subsequent chapters then systematically cover the different applications such as molecular computation, spin-crossover, light harvesting and as photocatalysts for the production of solar fuels.
The book provides an overview of functional metallosupramolecular materials that will be of interest to graduate students, academics and industrial chemists interested in supramolecular chemistry, materials science and the materials applications.
Herein we describe the synthesis and structural characterization of a [2x2] metallogrid of Zinc(II) and its ditopic bis(hydrazone) ligand, as well as the evaluation of their photo‐physical and electrochemical properties. The synthesis of the bis(hydrazone) involves an aromatic nucleophilic substitution followed by a condensation. Then, through complexation with Zinc(II) ions the [2x2] metallogrid was obtained. The bis(hydrazone) was subjected to UV light‐induced E/Z isomerization determining its kinetic constants through Nuclear Magnetic Resonance (NMR). A clear effect of the metal and the structure was observed on the redox potentials of the metallogrid and its ligand when studied by Cyclic Voltammetry (CV) and Osteryoung Square Wave Voltammetry (OSWV). All compounds were also studied through UV‐Vis and Fluorescence spectroscopy, observing, in some cases, a pronounced pH‐effect. Our results indicate that the photophysical properties of metallogrid can be tuned through the elimination of the acidic protons from the bis(hydrazone) ligands and, together with their electrochemical properties can be used as molecular switches. Bis(hydrazone)‐based metallogrid molecular switch: The UV photoisomerization of the bis(hydrazone) ligand resembles some samurai positions due to their similarity. When subjecting the corresponding [2x2] metallogrid of Zinc(II) to pH changes, a chemical tunning of its photo‐physical properties can be achieved.
Several ditopic ligands containing two tridentate bishydrazone coordination subunits and their Zn(II) and Cd(II) [2 × 2] grid-type complexes were prepared and their photoluminescent properties studied. A special attention was devoted to the influence of the orientation of the hydrazone group NNin the core of the ligands and their complexes. Its reversal from [pyridineNNpyrimidine] (L1) to [pyridineNNpyrimidine] (L2) has a strong impact on the observed absorption and emission behaviour of particular ligands (L1 and L2) as well as of their [2 × 2] grid assemblies. The further lateral functionalization of the ligands led to different emission quantum yields of the resulting grids, while their emission and absorption spectra varied very little. The simplest derivative L1 turned out to have the best performance with, for its Zn(II) complex, relatively high quantum yield 60%.
Synthesis towards the preparation of an unsymmetrical binucleating Schiff-base ligand, methyl-6-(2-(1-(2-hydroxyphenyl)ethylidene(hydrazinecarbonyl)picolinate (H2L) is discussed. It has been synthesized by reacting methyl 6-(hydrazinecarbonyl)picolinate with 2-hydroxy acetophenone. The ligand (H2L) comprises two different asymmetric binding pockets, however when reacted with Mn(II), Co(II), Cu(II) and Zn(II) salts, very stable self-assembled [2×2] grid complexes form regardless of the employed metal-to-ligand ratio. The obtained complexes [Mn4L4]·(CH3CN) (1), [Co4L4]·(CHCl3) (2), [Cu4L4]·(CHCl3) (3) and [Zn4L4] (4) have been fully characterized by physicochemical methods, including ESI mass spectrometry and X-ray crystallographic analyses, and their EPR, magnetic and redox properties are discussed. All discussed complexes self-assembled in ‘head-to-tail’ fashion leading to [2×2] grid architectures. Mn, Co and Cu grid complexes show weak to moderate antiferromagnetic coupling among the four metal centers. The high stability of the grid structures is in line with the lack of any observable dissociation or exchange between metal ions in solution. Complexes 1 and 2 show four quasi-reversible to irreversible oxidative responses in cyclic voltammograms at glassy carbon working electrode in 1,2-dichlorobenzene and at platinum working electrode in dichloromethane, respectively.
The iron(II) [2×2] grid complex Fe-8H has been synthesized and characterized. It undergoes spin-crossover (SCO) upon deprotonation of the hydrazine-based terpyridine-like ligand. The deprotonation patterns have been determined by X-ray crystallography and 1H NMR spectroscopy and discussed in relation to the spin state of the iron(II) centers which influences greatly the pKa of the ligand. The synthesis of the magnetically-silent zinc(II) analogue is also reported and its (de)protonation behavior has been characterized to serve as reference for the study of the Fe(II) grid complexes. DFT computations have also been performed in order to investigate how the successive deprotonation of the bridging ligands affects the SCO behavior within the grid.
We present the synthesis of two types of two–site symmetric bis(hydrazone) ligands (1 and 2) which contain two tridentate subunits suitable for metal ion complexation, with remarkable solubility in most organic solvents, contrary to other pyrimidine-based bis(hydrazones) used for the preparation of metallogrids. As expected, compounds 1 and 2 exhibit conformational changes when coordinated metal ions (Zn²⁺, Ni²⁺, Co²⁺) through the two terpyridine–like sites leading to the metal complexes 1a–c and 2a–c. The absorption spectra and redox properties of ligands 1 and 2 and of the metal complexes 1a–c and 2a–c are studied. Compounds 1 and 2 exhibit absorption spectra dominated by intense π–π∗ bands in the UV region, while the absorption spectra of the metal complexes 1a–c and 2a–c show intense bands in the UV region, due to the spin–allowed ligand–centred (LC) transitions, and in the visible, due to spin–allowed metal–to–ligand charge transfer (MLCT) transitions. Cyclic voltammetry and square wave voltammetry were carried out in order to establish the relevance of the complexation, and the grid formation in the redox potentials of the ligands 1 and 2.
Supramolecular reactions are of importance in many fields. We report herein three examples where complexes of hydrazone-based ligands are involved. A Ag2-double-helicate was converted, by treatment with Zn(OTf)2, into a Zn4-grid (exchange of metal ions and change of the nature of the initial complex). A Pb4-grid was converted, upon reaction with ZnCl2 or ZnBr2, into a Zn4-grid (exchange of metal ions, but conservation of the nature of the initial complex). The reverse conversions were also achieved. The fusion of a Ag2-double-helicate with another Ag2-double-helicate was performed (exchange of ligands, but conservation of the nature of the complexes) and resulted in a mixture of three helicates (two homostranded ones and one heterostranded one).
Allgemeingültige Gestaltungsprinzipien für polyheterocyclische Stränge und deren definierte molekulare Bewegung wurden entwickelt. Eine durch Effektoren modulierte Formveränderung induziert gezielt eine helikal-gefaltete oder linear-ausgedehnte Molekülgestalt. Durch die Koordination an Metallionen werden weitläufige molekulare Bewegungen ausgelöst, die durch den Zusatz konkurrierender Komplexierungsreagentien reversibel gemacht und durch sequenzielle Säure-Base-Neutralisation angetrieben werden können. Der Einbau von Hydrazongruppen in die Stränge verleiht die Fähigkeit zur konstitutionellen Dynamik, bei der Stränge mit verschiedenen Zusammensetzungen durch Komponentenaustausch ineinander umgewandelt werden. Diese Eigenschaften sind relevant für die Verwendung als nanomechanische Bauteile. Wir beschreiben die morphologische und funktionelle Analyse solcher in unserem Labor entwickelten Systeme.
General design principles have been developed for the control of the structural features of polyheterocyclic strands and their effector-modulated shape changes. Induced defined molecular motions permit designed enforcement of helical as well as linear molecular shapes. The ability of such molecular strands to bind metal cations allows the generation of coiling/uncoiling processes between helically folded and extended linear states. Large molecular motions are produced on coordination of metal ions, which may be made reversible by competition with an ancillary complexing agent and fueled by sequential acid/base neutralization energy. The introduction of hydrazone units into the strands confers upon them constitutional dynamics, whereby interconversion between different strand compositions is achieved through component exchange. These features have relevance for nanomechanical devices. We present a morphological and functional analysis of such systems developed in our laboratories.
In this review we describe some of most representative examples of metallosupramolecular architectures and dynamic hybrid materials recently published by our group in which supramolecular functional devices are constitutionally self-sorted by crystallization or by sol-gel polymerization. The self-selection is based on constitutional interactions resulting in the dynamic amplification of self-optimized architectures. The dynamic constitutional materials reported here therefore illustrate the convergence of the combinatorial self-sorting of dynamic combinatorial libraries (DCLs) with the specific self-optimized functions, extending the application of constitutional dynamic chemistry2 from materials science to functional constitutional devices.
Undergraduate research is limited by time available for research and research experience; of which time is probably the most important. Successful undergraduate research advisors can compensate for these limitations through setting realistic goals, matching research projects to the level of experience of their students, directly assisting in the lab, practicing good data management, and dividing projects over a large research group.
Four single crystal structures were obtained in order to better understand the difference between the crystallisation-driven formation of solid state organo-sulfonate guanidinium superstructures and their sodium salt analogues. 5-Formyl-2-furfuryl sulfonate and 4,4'-diamino-2,2'-biphenyl disulfonate were chosen as anions due to functional and geometrical considerations together with guanidinium, aminoguanidinium, and sodium cations. 5-Formyl-2-fufuryl sulfonate reacts with aminoguanidinium cation in water leading to an imino-zwitterionic compound, able to form on its own a guanidinium-sulfonate superstructure in crystalline state.
We describe herein the self-assembly processes as well as the structural properties of metallosupramolecular grid-architectures, involving bis-bidentate ligand 1, based on imino-pyridine complexation subunits and tetrahedrally (Cu+, Ag+) and octahedrally (Co2+, Zn2+, Fe2+) coordinated metal ions. The NMR, electrospray ionisation mass spectrometry data and X-ray crystal structure results suggest that in solution corner- and grid-type compounds are present, while in the solid state they adopt very compact and stable [2 × 2] grids arrays. Despite the variable binding behaviours of tetrahedrally coordinated cations (Cu+, Ag+) and the four coordination (lower) number of octahedrally coordinated cations (Co2+, Zn2+, Fe2+), the flexibility of the ligand 1 induce a perfect arrangement of these components, resulting in the formation of metallosupramolecular grids. Examination of such structures suggests that simple conformational rotation around the central phenyl of ligand 1 results in the self-assembly of chiral ligands. This allows the formation of mesomeric grid-type superstructures containing an inversion centre with half-superior and -inferior inner surfaces of opposite chirality.
Guest molecules confined inside hollow molecular assemblies and thus protected from their environment can show unexpected structural behavior or special reactivity compared to their behavior in a bulk, unprotected environment. A special case is the coiling behavior of variable-length alkane chains in rigid hydrogen-bonded molecular cages. It has been found before that coiling may occur in such circumstances, but no experimental evidence concerning the exact conformation of the chains has yet been presented. We reveal in this study the self-assembly of a molecular cage in water and the crystalline state from three distinct components in which linear 1,ω-diammonium-alkanes chains are confined with different degrees of compression. The exact coiling behavior is determined from atomic resolution X-ray diffraction showing crenel-like conformations in the compressed state. Chemical selection can be obtained from mixtures of alkane chains via the encapsulation of kinetically stable conformations observed during the encapsulation of pure components. Moreover, it was found that uncompressed and compressed chains can be competitively trapped inside the capsule. These findings may provide insight in areas to a better understanding of biological processes, such as the fatty acid metabolism.
This microreview reveals a new strategy to transcribe supramolecular architectures in self-organized constitutional hybrids. In particular, the use of communicating reversible-covalent and supramolecular hydrophobic interfaces between organic/supramolecular and inorganic/siloxane networks represents a useful approach for improving their compatibility. Interpenetrated hybrid components lead, after the sol–gel process, to materials in which the features of supramolecular and inorganic networks are expressed through cross-over and linear processing schemes. Such a “dynamic marriage” between the processes of supramolecular self-assembly and inorganic sol–gel polymerization, which communicate synergistically, leads to higher self-organized hybrid materials on increased micrometric scale. Considering the simplicity of this strategy, possible applications in membranes and sensors are effective, reaching close to novel expressions of complex matter.
The first tetratopic pyrimidine-hydrazone (pym-hyz) molecular strands containing terminal hydroxymethyl () and acryloyl () functional groups have been synthesised. was produced by step-wise imine condensation reactions, starting with 6-hydroxymethyl-2-pyridinecarboxaldehyde. was then synthesised through the treatment of with acryloyl chloride. NMR spectroscopy and X-ray crystallography showed that the ligands adopted a helical shape, comprised of 1 and 1/3 helical turns. Both and uncoiled upon reaction with an excess amount of Pb(ii), Zn(ii) and Cu(ii) ions, resulting in linear M4A8 complexes (where M = Pb(ii), Zn(ii), or Cu(ii); = or ; and A = ClO4(-), SO3CF3(-) or BF4(-)). Horse-shoe shaped Pb2A4 complexes were also formed by reacting Pb(ii) ions with either or in a 2 : 1 metal to ligand ratio. The addition of Ag(i) ions to either or resulted in Ag22A2 double helicates, which were stable in the presence of excess Ag(i). The Pb(ii), Zn(ii) and Ag(i) complexes were characterised by NMR spectroscopy, while UV-Vis spectroscopy was used to probe the Cu(ii) complexes. In addition, X-ray crystallography was used to analyse the linear Pb4A8, horse-shoe shaped Pb2(ClO4)4, twisted Cu3(SO3CF3)6, and double helicate Ag22(SO3CF3)2 complexes yielding the structures [Pb4(ClO4)7(H2O)]ClO4·4CH3NO2 (), [Pb4(SO3CF3)8]2·6CH3CN·H2O (), [Pb2(ClO4)2(CH3CN)(H2O)](ClO4)2·2CH3CN·C4H10O·H2O (), [Cu3(SO3CF3)3(CH3CN)2(H2O)](SO3CF3)3·2CH3CN·H2O () and [Ag22](SO3CF3)2·CH3CN·H2O (), respectively.
An investigation of the constitutional adaptive gelation process of chitosan/cinnamaldehyde (C/Cy) dynagels is reported. These gels generate timely variant macroscopic organization across extended scales. In the first stage, imine-bond formation takes place “in-water” and generates low-ordered hydrogels. The progressive formation of imine bonds further induces “out-of-water” increased reactivity within interdigitated hydrophobic self-assembled layers of Cy, with a protecting environmental effect against hydrolysis and that leads to the stabilization of the imine bonds. The hydrophobic swelling due to Cy layers at the interfaces reaches a critical step when lamellar self-organized hybrids are generated (24 hours). This induces an important restructuration of the hydrogels on the micrometric scale, thus resulting in the formation of highly ordered microporous xerogel morphologies of high potential interest for chemical separations, drug delivery, and sensors.
"Metal-driven" selection between finite mononuclear and polymeric metallosupramolecular species can be quantitatively achieved in solution and in a crystalline state via coupled coordination/stacking interactional algorithms within dynamic metallosupramolecular libraries - DMLs.
This study deals with the investigation of two low molecular weight Schiff base compounds with bromine end groups, differing only by the presence or absence of one methyl group, with the aim of better understanding the solution and the solid state optical, electrochemical and thermic properties generated by the small structural features. The compounds were structurally characterized by 1H NMR, 13C NMR and FTIR spectroscopies, single-crystal X-ray diffraction and gas chromatography analysis. Their thermal behavior was evidenced by polarized light microscopy and differential scanning calorimetry. The single crystal structure of the compounds reveals the versatility of bromine substituents which can adopt an attractive or repulsive electron effect, driven by the structural environment. A comparison of the structures shows that the introduction of a methyl unit as a bulky group hinders completely the p–p stacking interaction within the structural rows, inducing larger intermolecular distances resulting in quite different functional physical and chemical properties.
Four new grid forming hydrazone ligands substituted with methoxy and dimethylamino groups were synthesised. Combination of these ligands with zinc triflate in acetonitrile resulted in self-assembly to form grids as indicated by H NMR and ES-MS. H NMR also showed thermally induced rotation of the intercalated phenyl ring in both the new grids, and in three previously reported grid compounds. Of these seven, five were amenable to study by variable temperature H NMR. Though the observed rates varied by more than an order of magnitude depending upon ligand structure and level of deprotonation, activation energies were similar (∼60 kJ/mol) for all complexes studied. This suggests a model in which dissociation of the central pyrimidine ligand precedes phenyl group rotation with an enthalpy of dissociation near zero. The rate of rotation of the phenyl ring increases with an introduction of electron-donating substituents on the phenyl ring, possibly due to an increased repulsion between π systems.
Polypyridyl ligand derivatives have been widely employed for the construction of metallo-supramolecular entities from the beginning of this contemporary area of research. Representative recent developments in the use of such ‘classical’ polypyridyl ligands combined with selected d-block metal ions to obtain supramolecular assemblies incorporating both the polypyridyl and the metal ion as structural elements are described.In particular, helicates, metal-chain oligo-pyridylamido systems, grids as well as a range of other metallo-supramolecular structures are discussed.
A new tetracopper(II) complex [Cu4(bsbd)4] (bsbd=bis(N-salicylidene)benzene-1,4-diamine) has been prepared and structurally characterized. The complex constructs a [2×2] cyclic coordination framework, which inhibits formation of square planar copper(II) centers, and induces distortion to a tetrahedral structure. The effects of the distortions on the absorption spectra are characterized.
Solid-state X-ray crystal structure of the HgII grid-like complex [Hg414](CF3SO3)8 of the bis-tridentate ligand 1 obtained by condensation of bis(methylhydrazino)phenylpyrimidine with pyridine-2-carboxaldehyde was determined. It confirms the previous structure determined on the basis of 1D and 2D NMR studies. The amplitude of the extension of the ligand as a result of the formation of the grid was found to be of around 15 Å. The distance between the nitrogen atom of a molecule of acetonitrile and the centroid of the closest pyrimidine ring, and the distance between the oxygen atom of a triflate and the centroid of the closest pyrimidine ring are of about 3 Å, thus suggesting acetonitrile-π, respectively triflate-π interactions.
Nickel and cobalt complexes of pyridine-2-carboxaldehyde-2′-pyridylhydrazone (papyH) and N-methyl(pyridine-2-carboxaldehyde-2′-pyridyl-hydrazone) (papyMe) have been fully characterized through electrochemistry, titration, and alkylation with methyl iodide and compared with existing data on zinc and iron complexes. Both rate constants for alkylation and ligand pKa depend on the coordinated metal and can be understood based on the influence of d electrons on the ligand molecular orbitals.
A new ditopic pyrimidine-hydrazone ligand, 6-hydroxymethylacryloyl-2-pyridinecarboxaldehyde, 2,2'-[2,2'-(2-methyl-4,6-pyrimidinediyl)bis(1-methylhydrazone)] (L2), was synthesized with terminal acryloyl functional groups to allow incorporation into copolymer gel actuators. NMR spectroscopy was used to show that L2 adopted a horseshoe shape with transoid-transoid pym-hyz-py linkages. Metal complexation studies were performed with L2 and salts of Pb(II), Zn(II), Cu(II), and Ag(I) ions in CHCN in a variety of metal to ligand ratios. Reacting L2 with an excess amount of any of the metal ions resulted in linear complexes where the pym-hyz-py linkages were rotated to a cisoid-cisoid conformation. NMR spectroscopy showed that the acryloyl arms of L2 did not interact with the bound metal ions in solution. Seven of the linear complexes (1-7) were crystallized and analyzed by X-ray diffraction. Most of these complexes (4-7) also showed no coordination between the acryloyl arms and the metal ions; however, complexes 1-3 showed some interactions. Both of the acryloyl arms were coordinated to Pb(II) ions in [PbL2(SOCF)] (1), one through the carbonyl oxygen donor and the other through the alkoxy oxygen donor. One of the acryloyl arms of [CuL2(CHCN)](SOCF) (2) was coordinated to one of the Cu(II) ions through the carbonyl oxygen donor. There appeared to be a weak association between the alkoxy donors of the acryloyl arms and the Pb(II) ions of [PbL2(ClO)]·CHCN (3). Reaction of excess AgSOCF with L2 was repeated in CDNO, resulting in crystals of {[Ag(L2)(SOCF)(HO)] SOCF} (8), the polymeric structure of which resulted from coordination between the carbonyl donors of the acryloyl arms and the Ag(I) ions. In all cases the coordination and steric effects of the acryloyl arms did not inhibit isomerization of the pym-hyz bonds of L2 or the core shape of the linear complexes.
The synthesis and characterization of a series of halogen-substituted pseudoterpyridine Zn(II) homoleptic mononuclear complexes, based on ligands L(11)-L(44) [2,6-pyridinedicarboxaldehydebis(p-R-phenylimines), R = F, Cl, Br, I] are reported. Neither of the structures contain relatively strong classical hydrogen bonds (OH...O, NH...O, OH...N, NH...N) and the structure packing is thus determined by a subtle interplay of weaker interactions. Isostructurality of the four halogen analogues is very rare, and in this study -Br, -Cl and -F are found to be isostructural in different degrees, whereas -I is not. Interestingly, although it is closely isostructural to the -Cl and -Br compounds, the F analogue is shown not to form F...O bonds, while the Cl and the Br analogues do form Hal...O bonds. This raises an important question on the role of Hal...O bonds in the structuration of the crystal packing, particularly the stabilization effect. Similarly, while the CH...Hal interaction seems to give one-dimensional cohesion in the -Cl and -Br analogues, this feature is absent in the -F analogue, despite its close isostructurality. CH...O interactions appear to dominate to a first degree the cohesion between the anionic trifluoromethanesulfonate network and the cationic Zn-pyridinedicarboxaldehydebis(p-R-phenylimines) network. The analysis of these interactions is corroborated by reduced density gradient calculations based on promolecular densities.
The reaction between dpktch and CdCl2 in refluxing acetonitrile gave [CdCl2(η3-dpktch)] in good yield. Spectroscopic measurements divulge the coordination of dpktch and the elemental analysis confirmed its formulation. Optical measurements in N,N-dimethylformamide (dmf) and dimethylsulfoxide (DMSO) in the absence and presence of a proton donor/acceptor disclosed two highly sensitivity interlocked intra-ligand-charge-transfer transitions (ILCT) that are sensitive to their surroundings. Under basic conditions, a low-energy electronic transition with an extinction coefficient of 17,400 ± 2000 M−1cm−1 appeared at 403 nm and a peak minimum appeared at 326 nm. Under acidic conditions, a high energy electronic transition with extinction coefficient of 13,500 ± 2000 M−1cm−1 appeared at 330 nm and a shoulder appeared at 400 nm. The addition of an acid to a dmf solution of [CdCl2(η3-dpktch)] caused the disappearance of the low energy absorption band at 403 nm and a peak maximum appeared at 330 nm. The reverse was observed when a base was added to a DMSO solution of [CdCl2(η3-dpktch)]. Electrochemical measurements reveal reduction of coordinated CdCl2 and oxidation of electrodeposited cadmium metal along with ligand-based redox processes. X-ray crystallographic analysis on a monoclinic, P21/n single crystal of [CdCl2(η3-dpktch)], confirmed the N,N,O-coordination of dpktch and revealed digitated units of [CdCl2(η3-dpktch)] interlocked via a web of hydrogen bonds.
The concomitant operation of dynamic covalent frameworks and metallodynamers results in the formation of selective Zn(2+)-based dynameric membranes for restrictive facilitated and selective transport of CO(2).
Data on the metal complexes with bis(hydrazones) obtained from various classes of dicarbonyl compounds are generalized and described systematically. The structure and complexing properties of bis(hydrazones) are considered and the factors influencing structures of the metal complexes are analyzed. The relationships between the structures and physicochemical properties of the considered compounds are discussed. © 2009 Russian Academy of Sciences and Turpion Ltd.
A new bis-tetradentate acyclic amine ligand L(Et) has been synthesized from 4,6-bis(aminomethyl)-2-phenylpyrimidine and 2-vinylpyridine. Dinuclear complexes, Mn(II)(2)L(Et)(MeCN)(H(2)O)(3)(ClO(4))(4) (1), Fe(II)(2)L(Et)(H(2)O)(4)(BF(4))(4) (2), Co(II)(2)L(Et)(H(2)O)(3)(MeCN)(2)(BF(4))(4) (3), Ni(II)(2)L(Et)(H(2)O)(4)(BF(4))(4) (4), Ni(II)(2)L(Et)(H(2)O)(4)(ClO(4))(4)·8H(2)O (4'), Cu(II)(2)L(Et)(BF(4))(4)·MeCN (5), Zn(II)(2)L(Et)(BF(4))(2)(BF(4))(2)·½MeCN (6), were obtained from 1 : 2 reactions of L(Et) and the appropriate metal salts in MeCN, whereas in MeOH tetranuclear complexes, Mn(II)(4)(L(Et))(2)(OH)(4)(ClO(4))(4) (7), Fe(II)(4)(L(Et))(2)(F)(4)(BF(4))(4)·5/2H(2)O (8), Co(II)(4)(L(Et))(2)(F)(4)(BF(4))(4)·3H(2)O (9), Ni(II)(4)(L(Et))(2)(F)(4)(BF(4))(4)·4H(2)O (10), Cu(II)(4)(L(Et))(2)(F)(4)(BF(4))(4)·3H(2)O (11) and Zn(II)(4)(L(Et))(2)(F)(4)(BF(4))(4) (12), result. Six complexes have been structurally characterized: in all cases each L(Et) is bis-tetradentate and provides a pyrimidine bridge between two metal centres. As originally anticipated, complexes 1, 4' and 6 are dinuclear, while 9, 10 and 12 are revealed to be tetranuclear, with two M(2)(L(Et))(4+) moieties bridged by two pairs of fluoride anions. Weak to moderate antiferromagnetic coupling between the metal centres is a feature of complexes 2, 3, 4, 8, 9 and 10. The dinuclear complexes 1-6 undergo multiple, mostly irreversible, redox processes. However, the pyrimidine-based dicopper(II) complex 5 undergoes a two electron quasi-reversible reduction, Cu(II)(2)→ Cu(I)(2), and this occurs at a more positive potential [E(m) = +0.11 V (E(pc) = -0.03 and E(pa) = +0.26 V) vs. 0.01 M AgNO(3)/Ag] than for either of the dicopper(II) complexes of the analogous pyrazine-based ligands.
We describe here a study of the coordination binding of Co 2+ , Cu 2+ and Pb 2+ ions to the ditopic ligand 1, leading to the formation of rack-type and double helical monomers. We report the crystal structures of three such complexes 5-7, which further self-organize into complementary duplex-rack, square and double helical architectures in the solid state. The ligand 1 discussed in this paper operates under conditions in which the two terpyridine (terpy) coordination sites resulted from Pyridine-Pyridine-Pyridazine connected sequences can be involved in the orthogonal binding events of the octahedral metal ions. In terms of molecular adaptability the formation of rack-type and double helical architectures represents the best coordination frameworks of the rigid ligand 1 presenting unfavorable orientation of coordination vectors. In terms of programmed self-assembly the formation of the different metallo-architectures 5, 6 and 7 underlines the fact that, despite the role of the strength of the coordination interactions and of maximal site occupation, other factors like stacking, binding of anions (triflate or tetrafluoroborate anions stabilizing the network of metallic ions) and of solvent molecules may interfere and influence the nature of the favored output species.
Diffusionsgewichtete NMR-Experimente (DOSY) wurden genutzt, um eine dynamische kombinatorische Bibliothek aus helicalen Strängen und gitterförmigen metallosupramolekularen Architekturen zu charakterisieren. Diese Technik ermöglicht die Entfaltung sehr ähnlicher chemischer Strukturen, die sich lediglich in ihrem hydrodynamischen Radius unterscheiden. Außerdem können sprungfederartige Konformationsbewegungen in helicalen Strängen als Funktion der Temperatur detektiert werden.
The adequate selection of macromonomers, dialdehyde core connectors and of coordinating metal ions makes possible the generation of metallodynameric materials, allowing the fine modulation of the gas transport through rubbery membranes.
Four 4'-hydrazone derivs. of 2,2':6',2"-terpyridine which vary in their N- and C-substitution in the R'NN=CRPh unit have been prepd. and structurally characterized. Protonation studies and soln. behavior of these compds. are described, as well as representative crystal structures of mono- and diprotonated derivs. In the solid-state structures of each neutral compd., the tpy domain adopts the anticipated trans,trans-conformation, and intramol. steric factors compete with π-stacking effects to control the amt. to which the C-Ph substituent twists out of the plane of the tpy unit. When R' = H, the imine NH group engages in hydrogen bonding interactions in the solid state, except where R = Ph. In soln., variable temp. 1H NMR spectroscopy shows that on going from R = Me to Ph (with R' = H), the barrier to rotation about the Cpy-Nimine bond increases; with R = R' = H, the hydrogen bonding capabilities of the solvent to the imine NH influence this dynamic process. In the N-Me deriv. (R = H and R' = Me), rotation about the Cpy-Nimine bond is facile at room temp. Protonation of the deriv. with R = R' = H results in an increase in the activation barrier to rotation, consistent with a greater π-contribution to the Cpy-Nimine bond. [on SciFinder(R)]
Five substituted 2,2':6',2''-terpyridin-4'-yl hydrazones, tpy-4'-NHN:CMe2 (5, tpyH = 2,2':6',2''-terpyridine) and tpy-4'-NHN:CHAr [6-9, Ar = 4-BrC6H4, 4-NO2C6H4, 4-MeOC6H4, 3,5-(MeO)2C6H3] functionalized in the 4'-position with a hydrazone substituent were prepd. and characterized by single-crystal x-ray structural anal. Protonation of the tpy domain of the ligands is facile. Soln. behavior was studied by NMR and electronic spectroscopies. Representative structural data are presented for neutral and monoprotonated ligands, and illustrate that H-bonding involving the formal amine NH unit is a dominant structural motif in all cases. [on SciFinder(R)]
A new 1,5-dipyridyl verdazyl, synthesized from the corresponding dipyridyl hydrazone, coordinates nickel(II) to form a structurally characterized, pseudooctahedral complex analogous to Ni(terpy)(2)(2+). The unusually short Ni-verdazyl distance results in strong ferromagnetic exchange (J(Ni-rad) = + 300, J(rad-rad) = + 160 cm(-1)) between all three paramagnetic species along with a metal-ligand charge transfer band in the electronic spectrum.
An unsymmetrical bis(tridentate) ligand LH in which one binding site can be readily deprotonated forms a kinetically inert [Co(III)L(2)](+) complex which can be used as a "corner" species for the "Coupe du Roi" assembly of trans,trans-[Co(2)M(2)L(4)](6+) metallogrids (M = Fe(II), Co(II), Cu(II), Zn(II)). In the mixed Co(III)/Co(II) species, the oxidation states appear to be localised. In solution, the ligand LH forms octacationic, homometallic [2 × 2] grids with the individual labile metal ions Fe(II), Co(II), Cu(II), Zn(II), seemingly as mixtures of all possible isomers arising from the unsymmetrical nature of the ligand. In the solid state, however, [Zn(4)L(4)](CF(3)SO(3))(8)·4CH(3)CN crystallises as a single species where the cation has S(4) symmetry. This stereoselectivity in the crystalline lattice is associated with interactions between the cation and triflate anions which can again be analysed in terms of the Coupe du Roi concept.
Metal complexation studies were performed with the ditopic pyrimidine-hydrazone (pym-hyz) strand 6-hydroxymethylpyridine-2-carboxaldehyde (2-methyl-pyrimidine-4,6-diyl)bis(1-methylhydrazone) (1) and Pb(ClO(4))(2)·3H(2)O, Pb(SO(3)CF(3))(2)·H(2)O, Zn(SO(3)CF(3))(2), and Zn(BF(4))(2) to examine the ability of 1 to form various supramolecular architectures. X-ray crystallographic and NMR studies showed that coordination of the Pb(II) salts with 1 on a 2:1 metal/ligand ratio in CH(3)CN and CH(3)NO(2) resulted in the linear complexes [Pb(2)1(ClO(4))(4)] (2), [Pb(2)1(ClO(4))(3)(H(2)O)]ClO(4) (3), and [Pb(2)1(SO(3)CF(3))(3)(H(2)O)]SO(3)CF(3) (4). Two unusually distorted [2 × 2] grid complexes, [Pb1(ClO(4))](4)(ClO(4))(4) (5) and [Pb1(ClO(4))](4)(ClO(4))(4)·4CH(3)NO(2) (6), were formed by reacting Pb(ClO(4))(2)·6H(2)O and 1 on a 1:1 metal/ligand ratio in CH(3)CN and CH(3)NO(2). These grids formed despite coordination of the hydroxymethyl arms due to the large, flexible coordination sphere of the Pb(II) ions. A [2 × 2] grid complex was formed in solution by reacting Pb(SO(3)CF(3))(2)·H(2)O and 1 on a 1:1 metal/ligand ratio in CH(3)CN as shown by (1)H NMR, microanalysis, and ESMS. Reacting the Zn(II) salts with 1 on a 2:1 metal/ligand ratio gave the linear complexes [Zn(2)1(H(2)O)(4)](SO(3)CF(3))(4)·C(2)H(5)O (7) and [Zn(2)1(BF(4))(H(2)O)(2)(CH(3)CN)](BF(4))(3)·H(2)O (8). (1)H NMR studies showed the Zn(II) and Pb(II) ions in these linear complexes were labile undergoing metal ion exchange. All of the complexes exhibited pym-hyz linkages in their cisoid conformation and binding between the hydroxymethyl arms and the metal ions. No complexes were isolated from reacting either of the Zn(II) salts with 1 on a 1:1 metal/ligand ratio, due to the smaller size of the Zn(II) coordination sphere as compared to the much larger Pb(II) ions.
Molecular architectures and materials can be constitutionally self-sorted in the presence of different biomolecular targets or external physical stimuli or chemical effectors, thus responding to an external selection pressure. The high selectivity and specificity of different bioreceptors or self-correlated internal interactions may be used to describe the complex constitutional behaviors through multistate component selection from a dynamic library. The self-selection may result in the dynamic amplification of self-optimized architectures during the phase change process. The sol-gel resolution of dynamic molecular/supramolecular libraries leads to higher self-organized constitutional hybrid materials, in which organic (supramolecular)/inorganic domains are reversibily connected.
A pentanuclear M(5)L(6) coordination cage is self-assembled in solution from a rigid linear heteroditopic phen-tpy ligand and an iron (II) salt.
The synthesis and characterization of 6-hydroxymethylpyridine-2-carboxaldehyde (2-methyl-pyrimidine-4,6-diyl)bis(1-methylhydrazone) (1) is reported. Ligand 1 was designed as a ditopic pyrimidine-hydrazone molecular strand with hydroxymethyl groups attached to the terminal pyridine rings. Coordination of 1 with Cu(ClO(4))(2) x 6 H(2)O or Cu(SO(3)CF(3))(2) x 4 H(2)O in a 1:2 molar ratio resulted in the dinuclear Cu(II) complexes [Cu(2)1(CH(3)CN)(4)](ClO(4))(4) x CH(3)CN (4) and [Cu(2)1(SO(3)CF(3))(2)(CH(3)CN)(2)](SO(3)CF(3))(2) x CH(3)CN (5). X-ray crystallography and (1)H NMR NOESY experiments showed that 1 adopted a horseshoe shape with both pyrimidine-hydrazone (pym-hyz) bonds in a transoid conformation, while 4 and 5 were linear in shape, with both pym-hyz bonds in a cisoid conformation. Coordination of 1 with Cu(ClO(4))(2) x 6 H(2)O or Cu(SO(3)CF(3))(2) x 4 H(2)O in a 1:1 molar ratio resulted in three different bent complexes, [Cu(1H)(ClO(4))(2)](ClO(4)) (6), [Cu(1H)(CH(3)CN)](ClO(4))(3) x 0.5 H(2)O (7), and [Cu1(SO(3)CF(3))](2)(SO(3)CF(3))(2) x CH(3)CN (8), where the pym-hyz bond of the occupied coordination site adopted a cisoid conformation, while the pym-hyz bond of the unoccupied site retained a transoid conformation. Both 6 and 7 showed protonation of the pyridine nitrogen donor in the empty coordination site; complex 8, however, was not protonated. A variety of Cu(II) coordination geometries were seen in structures 4 to 8, including distorted octahedral, trigonal bipyramidal, and square pyramidal geometries. Coordination of the hydroxymethyl arm in the mononuclear Cu(II) complexes 6, 7, and 8 appeared to inhibit the formation of a [2 x 2] grid by blocking further access to the Cu(II) coordination sphere. In addition, the terminal hydroxymethyl groups contributed to the supramolecular structures of the complexes through coordination to the Cu(II) ions and hydrogen bonding.
Polytopic ligand design involves matching the coordination pocket composition with the metal ion coordination 'algorithm', but despite targeting [4 x 4] grids as the final outcome, metal ion preferences and ligand control can lead to widely varying complexes in the self-assembly process with Ni(II) and Cu(II).
Die bisher höchste Zahl gut aufgelöster, reversibler Reduktionswellen einer molekularen Verbindung wird bei der schrittweisen Reduktion des vierkernigen Co-[2×2]-Gitterkomplexes 1 (R=Ph) durch insgesamt elf Elektronen beobachtet. Die zehn gut aufgelösten, vollkommen reversiblen Reduktionsschritte im zugehörigen (differentiellen) Cyclovoltammogramm (siehe Diagramm) stehen für zehn reduzierte Spezies von überraschender Stabilität.
Synthetic organic chemists enjoy the luxury of having a large collection of reliable reactions at their disposal for preparing small molecules, mesoscopic structures, and polymers. Coordination chemists, on the other hand, are faced with the fact that transition metal chemistry, when normalized for the number of transition metals, has relatively few high-yielding reactions, when compared to the chemistry of carbon, for preparing even small molecule structures. This lack of control is manifested, in large part, in the weak metal–ligand interactions found in coordination complexes as compared with the strong covalent bonds in organic compounds. Weak bonding often translates into many reaction pathways that are not substantially different from an energetic point of view, and therefore, results in poor selectivity. As a result, many coordination chemists in recent years have come to the realization that it may be easier and more productive to develop straightforward and reliable routes to mesoscopic supramolecular structures by capitalizing on the modest collection of high-yielding reactions in coordination chemistry, the directional bonding afforded by metal centers, and strategies aimed at taking advantage of the weak metal bonds found in coordination complexes. Three emerging synthetic strategies, the symmetry-interaction, directional-bonding, and weak-link synthetic approaches, all use metal centers as structural building blocks to rationally assemble molecular components into supramolecular metallocyclophanes. These three approaches are discussed herein, and the fundamental principles underlying each as well as their capabilities are compared and contrasted.
Durch Selbstorganisation von fünfzehn Komponenten in einem Schritt – Ag ⁺ ‐Ionen und sechs starren, linearen 6,6′‐Bis[2‐(6‐methylpyridyl)]‐3,‐′‐bipyridazin‐Liganden – entsteht das im Bild rechts schematisch dargestellte 3 × 3‐Gitter. Neue physikalisch‐chemische Eigenschaften und die Möglichkeit zur Informationsspeicherung wird von dieser Art supramolekularer Strukturen erwartet. magnified image
The oxidation state of the cobalt centres can be controlled by modification of the protonation state in [2 × 2] grid-like arrays based on ionisable bis(hydrazone) ligands, allowing conversion of the paramagnetic CoII4 into the diamagnetic CoIII4 grid.
The new bis-hydrazone based ligands A and B form ionisable [2 × 2] grid-type transition metal complexes whose properties may be modulated by multiple protonation/deprotonation as shown by the reversible change in optical properties of the [CoII4L4]8+ complexes depending on their protonation state.
In dilute aqueous solution pyridine-2-aldehyde-2-pyridylhydrazone (PAPHY) is a diacid base with acid dissociation constants pk1 = 2.87 and pk2 = 5.71. Stability constants have been measured for complexes of this base with Mn, Fe, Ni, Cu, Zn, and Cd, all in the +2 oxidation state. The Fe(II) complex is exceptionally stable. In strongly alkaline solution the neutral PAPHY molecule undergoes a third, very feebly acid dissociation with pk3 between 14 and 15. The marked effect of metal coordination upon this third dissociation has been quantitatively examined.
π‐Stapel‐Wechselwirkungen der quasiparallelen 3,6‐Bis(2‐pyridyl)‐pyridazin(dppn)‐Liganden bewirken wahrscheinlich die Verzerrung der planaren Cu 4 ‐Einheit in 1 vom Quadrat zur Raute. Jedes Cu‐Atom ist dabei tetraedrisch von zwei N‐Atomen der Pyridin‐und zwei N‐Atomen der Pyridazinringe umgeben, wobei die Chelatringe planar sind. Der Abstand zwischen den paarweise angeordneten dppn‐Liganden be trägt 3.47 Å magnified image
This article deals with a coordination approach to
three-dimensional assemblies via
‘molecular
paneling’. Families of planar exo-multidentate organic ligands
(molecular panels) are found to assemble into large three-dimensional
assemblies through metal-coordination. In particular,
cis-protected square planar metals, (en)Pd2+ or
(en)Pt2+ (en = ethylenediamine), are shown to be very useful to
panel the molecules. Metal-assembled cages, bowls, tubes, capsules, and
polyhedra are efficiently constructed by this approach.
Mit zweifach dreizähnigen Liganden L gelang die Synthese von strukturchemisch bemerkenswerten Vierkern‐Co II ‐Komplexen: Das Komplexkation [Co 4 (L) 4 ] ⁸⁺ 1 weist ein [2 × 2]‐Gitter mit oktaedrisch koordinierten Metallionen auf, die an den Ecken eines Viereckes sitzen. Der Komplex geht vielfältige Redoxreaktionen ein und ist z. B. interessant für die Entwicklung elektrochemisch adressierbarer anorganischer Architekturen (R ¹ , R ² = H, Me; • = Co II ). magnified image
Part 1 From molecular to supramolecular chemistry: concepts and language of supramolecular chemistry. Part 2 Molecular recognition: recognition, information, complementarity molecular receptors - design principles spherical recognition - cryptates of metal cations tetrahedral recognition by macrotricyclic cryptands recognition of ammonium ions and related substrates binding and recognition of neutral moelcules. Part 3 Anion co-ordination chemistry and the recognition of anionic substrates. Part 4 Coreceptor molecules and multiple recognition: dinuclear and polynuclear metal ion cryptates linear recognition of molecular length by ditopic coreceptors heterotopic coreceptors - cyclophane receptors, amphiphilic receptors, large molecular cage multiple recognition in metalloreceptors supramolecular dynamics. Part 5 Supramolecular reactivity and catalysis: catalysis by reactive macrocyclic cation receptor molecules catalysis by reactive anion receptor molecules catalysis with cyclophane type receptors supramolecular metallo-catalysis cocatalysis - catalysis of synthetic reactions biomolecular and abiotic catalysis. Part 6 Transport processes and carrier design: carrier-mediated transport cation-transport processes - cation carriers anion transport processes - anion carriers coupled transport processes electron-coupled transpoort in a redox gradient proton-coupled transport in a pH gradient light-coupled transport processes transfer via transmembrane channels. Part 7 From supermolecules to polymolecular assemblies: heterogeneous molecular recognition - supramolecular solid materials from endoreceptors to exoreceptors - molecular recognition at surfaces molecular and supramolecular morphogenesis supramolecular heterogeneous catalysis. Part 8 Molecular and supramolecular devices: molecular recognition, information and signals - semiochemistry supramolecular photochemistry - molecular and supramolecular photonic devices light conversion and energy transfer devices photosensitive molecular receptors photoinduced electron transfer in photoactive devices photoinduced reactions in supramolecular species non-linear optical properties of supramolecular species supramolecular effects in photochemical hole burning molecular and supramolecular electronic devices supramolecular electrochemistry electron conducting devices - molecular wires polarized molecular wires - rectifying devices modified and switchable molecular wires molecular magnetic devices molecular and supramolecular ionic devices tubular mesophases. (Part contents).
Die gezielte Einführung unterschiedlicher Metallionen an definierten Positionen wurde beim Aufbau von [2×2]-Gitterkomplexen erreicht (siehe schematische Darstellung; die schwarzen Balken symbolisieren ditope Liganden und die Kreise unterschiedliche Metallionen). Diese Methode für den Aufbau anorganischer Architekturen macht den Weg frei für viele neue Entwicklungen.
Alternating pyridine-pyrimidine oligomers 1, 2, and 3, composed of nineteen, twenty one, and twenty seven heterocycles, respectively, have been synthesized in stepwise fashion and characterized. Examination of their 1H NMR spectra revealed that these achiral nonbiological oligomers organize spontaneously into multiturn helical structures 1A-3A in solution, as indicated by marked upfield shifts of the aromatic protons coupled with distinct NOE effects. In view of their potential electron-acceptor properties compounds 1-3 also represent coiled wires of nanometric lengths, up to about 90 Å for 3 in its extended form. The helical structure has been confirmed for 1 in the solid state by X-ray crystallography; a chiral channel arrangement involving only one helical enantiomer was found despite of the lack of chiral center in the strand. The oligomers exhibit a broad structureless fluorescence with a large Stokes shift, attributable to intramolecular pyridine excimer emission resulting from the helical ordering. Variable-temperature 1H NMR experiments revealed that the oligomers exist as equilibrating mixtures of right-handed and left-handed helices. The barrier for helical handedness reversal was found to be independent on the length of the strand; two-(6), three-(1), and four-turn (3) helices showed comparable free energies of activation. Based on these observations, a stepwise folding mechanism involving two perpendicularly twisted pyridine-pyrimidine units in the transition states may be proposed for the helicity inversion processes. The present results together with earlier work indicate that the pyridine-pyrimidine sequence may be considered as a helicity codon, enforcing the formation of helical structures on the basis of intramolecular structural information.
Control over the folding of molecular strands may be achieved by appropriate choice of the constituting subunits, in particular for chains of specific heterocycles such as sequences of directly connected pyridine (py) and pyrimidine (pym) rings, which are known to fold into extended helical structures. Since the hydrazone (hyz) group represents an isomorphic analogue of a py site, the condensation of hydrazine and carboxaldehyde derivatives of pym offers a very efficient approach to strands incorporating hyz instead of py units and constituted by sequences of alternating hyz and pym groups. A series of such strands of different lengths, up to ten hyz units, i.e., 1–7, were synthesized. Their spectral properties indicate that they fold indeed into helical shapes. Extensive characterization was performed in solution by 1HNMR spectroscopy and in the solid state by determination of the crystal structures of eight such strands. They all display the expected helical geometry with up to 3 1/3 turns and direct stacking contacts. The efficiency and flexibility of the synthetic approach as well as its wide potential for generation of diversity through lateral decoration make the (hyzpym) subunit a particularly attractive helicity codon.
Jüngste Entwicklungen auf dem Gebiet der supramolekularen Koordinationschemie haben Übergangsmetallkomplexe mit Gitterstruktur ins Blickfeld der Forschung gerückt. Die Synthesen dieser komplexen molekularen Einheiten beruhen auf Selbstorganisationsprozessen, in denen die Zielverbindungen durch Koordination organischer Liganden an Metallionen in einer Stufe aus einer Vielzahl von Komponenten thermodynamisch gesteuert aufgebaut werden. Die organischen Liganden und die Metallionen bestimmen die photophysikalischen, elektrochemischen und magnetischen Eigenschaften der Gitterkomplexe, zusätzlich können jedoch auch “kollektive” Eigenschaften auftreten. Funktionelle Gitterkomplexe sind interessant für die Nanotechnologie, z. B. hinsichtlich der Entwicklung einer (supra)molekularen Informationsspeicherung und -verarbeitung. Das Aufbringen dieser Komplexe auf Oberflächen führt zu ausgedehnten matrixartigen Anordnungen von Metallionen mit bisher unerreichten Dichten adressierbarer Elemente.
The condensation of the two oligoheterocyclic aldehydes 8 and 16 with the bis-hydrazine 17 gives the bis-hydrazones 1 and 2. These molecular strands are shown to adopt helical conformations of 1.5 and 2.5 turns, respectively. The helical shape of 1 has been confirmed and structurally characterized by X-ray crystallography. The results indicate that the pyrimidine-hydrazone unit is a satisfatory helicity codon, so that the facile hydrazone formation provides an efficient procedure for generating helical structures. This greatly widens the scope of the methodology based on designed heterocyclic sequences for enforcing helicity in molecular strands, and opens interesting routes towards a variety of derived structures.
Modern coordination chemistry has the expanding ability to mimic form and structure in biology. This review highlights the diversity of architectural motifs currently known in coordination chemistry. It highlights the role of metal-directed self-assembly in their formation. Further, the review establishes general principles for the description of structural complexity in coordination compounds along the lines of that employed in biology.
Beyond molecular chemistry based on the covalent bond, supramolecular chemistry aims at developing highly complex chemical
systems from components interacting through noncovalent intermolecular forces. Over the past quarter century, supramolecular
chemistry has grown into a major field and has fueled numerous developments at the interfaces with biology and physics. Some
of the conceptual advances and future challenges are profiled here.
As the wind of time blows into the sails of space, the unfolding of the universe nurtures the evolution of matter under the pressure of information. From divided to condensed and on to organized, living, and thinking matter, the path is toward an increase in complexity through self-organization.
We provide a summary of our results in three-dimensional, coordination-driven self-assembly based on the directional-bonding methodology, in which the stoichiometric mixing of complementary building blocks, with appropriate, predefined geometries, leads to targeted, nanoscopic cages. Using this motif, we have synthesized high-symmetry ensembles resembling the Platonic solids, such as dodecahedra, and the Archimedean solids, such as truncated tetrahedra and cuboctahedra, as well as other cages, like trigonal bipyramids, adamantanoids, and trigonal prisms. The synthesis and characterization of these compounds is discussed, as is some host-guest chemistry.
The [M(4)(II)L(4)](8+) [2 x 2]-grid-type complexes 1-8 present a set of features of particular interest for potential applications. All complexes exhibit multiple reduction levels at low reduction potentials paired with rather high stability. The modulation of the reduction potentials is possible by introduction of appropriate substituents on the ligands. The Co(II)(4) complexes 1-5 present a remarkable regularity in the disposition of the reduction levels, indicating the ability of the Co(II) sites to transmit electronic interactions between reduced ligands. In general, all investigated molecular systems 1-8 show characteristics typical for multilevel supramolecular electronic devices.
The magnetism of a series of tetranuclear complexes of the [Fe4IIL4]8+ [2x2]-grid-type was investigated, revealing the occurrence of spin transition behavior within this class of compounds. The phenomenon depends directly on the nature of the substituent R(1) in the 2-position on the central pyrimidine group of the ligand L. All Fe(II) ions in compounds with R(1) substituents favoring strong ligand fields (R(1)=H; OH) remain completely in the diamagnetic low-spin state. Only complexes bearing R(1) substituents attenuating the ligand field by steric (and to a lesser extent electronic) effects (R(1)=Me; Ph) exhibit spin transition behavior triggered by temperature. In general, gradual and incomplete transitions without hysteresis were observed for magnetically active complexes. The systems described provide approaches to the development of (supra)molecular spintronics.
Regioselective, redox, and chiroselective features were used in a three-tiered synthesis to construct CoM [2×2] grid-type arrays (MII=CoII, ZnII, FeII; see picture). The assemblies are based on a bis(hydrazone) ligand containing ionizable and non-ionizable compartments. This route allows the cobalt oxidation state to be selectively modified according to the charge on the hydrazone moiety.
Hierarchical self-assembly of complex supramolecular architectures allows for the emergence of novel properties at each level of complexity. The reaction of the ligand components A and B with Fe(II) cations generates the [2x2] grid-type functional building modules 1 and 2, presenting spin-transition properties and preorganizing an array of coordination sites that sets the stage for a second assembly step. Indeed, binding of La(III) ions to 1 and of Ag(I) ions to 2 leads to a 1D columnar superstructure 3 and to a wall-like 2D layer 4, respectively, with concomitant modulation of the magnetic properties of 1 and 2. Thus, to each of the two levels of structural complexity generated by the two sequential self-assembly steps corresponds the emergence of novel functional features.
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