Coordination-driven self-assembly in a single pot

New multinuclear discrete heteroleptic complexes have been synthesized by mixing Pd(II), 2,2′-bipyridine and N,N′-(1,2-phenylene)diisonicotinamide in a single pot as a new approach. A dimeric molecular rhombus and a trimer in equilibrium are obtained where the dimer is the major product. Similar equilibrium is also observed when classical method is employed for the synthesis. The equilibrium is shifted exclusively in favour of the dimer upon addition of benzene. The complexes are characterized by NMR and ESI-MS methods. Crystal structure of the benzene encapsulated rhombus is presented.     

Coordination-driven self-assembly: solids with bidirectional porosity

Coordination-driven self-assembly reactions have been used in the preparation of a variety of discrete supramolecular species, some of which have shown promise as synthetic receptors. Many highly ordered coordination polymers and porous networks have been prepared in a similar fashion. While a few of these solids are capable of the uptake of small organic molecules in the resultant molecular channels, the formation of truly porous structures has frequently been thwarted by lattice interpenetration. A strategy for the formation of porous solids that may circumvent this problem is based on the covalent construction of nanoscale macrocycles which, when eclipsed in the solid state, may lead to porous, tubular assemblies. We have incorporated these concepts toward the realization of a bidirectionally porous solid. The metal-directed, self-assembly of a conjugated, macrocyclic ligand provides a discrete, supramolecular entity in solution and the solid state. X-ray crystallographic analysis establishes that this assembly packs such that bidirectional channels are realized, and the incorporation of only ClCH2CH2Cl into the crystal lattice demonstrates that these channels are potentially suitable for the selective uptake of small organic guests.     

Biradical with a polyfluorinated terphenylene backbone

Russian Chemical Bulletin - A method was developed for the synthesis of perfluoro-1,1′:4′,1″-terphenyl by the reaction of chloroperfluorobenzene with zinc dust followed by the...     

Coordination-driven self-assembly directs a single-crystal-to-single-crystal transformation that exhibits photocontrolled fluorescence

Coordination-driven self-assembly is employed to direct a single-crystal-to-single-crystal [2 + 2] photodimerization that exhibits tunable fluorescence.     

Coordination-driven inversion of handedness in ligand-modified PNA

Peptide nucleic acid (PNA) is a synthetic analogue of DNA, which has the same nucleobases as DNA but typically has a backbone based on aminoethyl glycine (Aeg). PNA forms duplexes by Watson Crick hybridization. The Aeg-based PNA duplexes adopt a chiral helical structure but do not have a preferred handedness because they do not contain a chiral center. An L-lysine situated at the C-end of one or both strands of a PNA duplex causes the duplex to preferably adopt a left-handed structure. We have introduced into the PNA duplexes both a C-terminal L-lysine and one or two PNA monomers that have a γ-(S)-methyl-aminoethyl glycine backbone, which is known to induce a preference for a right-handed structure. Indeed, we found that in these duplexes the γ-methyl monomer exerts the dominant chiral induction effect causing the duplexes to adopt a right-handed structure. The chiral PNA monomer had a 2,2':6',2'-terpyridine (Tpy) ligand instead of a nucleobase and PNA duplexes that contained one or two Tpys formed [Cu(Tpy)(2)](2+) complexes in the presence of Cu(2+). The CD spectroscopy studies showed that these metal-coordinated duplexes were right-handed due to the chiral induction effect exerted by the S-Tpy PNA monomer(s) except for the cases when the [Cu(Tpy)(2)](2+) complex was formed with Tpy ligands from two different PNA duplexes. In the latter case, the metal complex bridged the two PNA duplexes and the duplexes were left-handed. The results of this study show that the preferred handedness of a ligand-modified PNA can be switched as a consequence of metal coordination to the ligand. This finding could be used as a tool in the design of functional nucleic-acid based nanostructures.     

Coordination-driven self-assembly of predesigned supramolecular triangles

The design and self-assembly of three supramolecular triangles is described. A novel 60 degrees corner unit directs the exclusive formation of triangular assemblies that are not in detectable equilibrium with other macrocycles. The resulting triangles have sides ranging from 2.7 to 3.5 nm in length and molecular masses as high as 5396 amu. The crystal structure of one of the assemblies shows an approximately 1.4 nm cavity; the crystal packing forms open, triangular channels. The characterization of the supramolecular triangles by multinuclear NMR, elemental analysis, and electrospray mass spectrometry is also reported.     

Silver-layered double hydroxides self-assemblies

New inorganic ensembles type layered double hydroxides enriched with silver ions were investigated in terms of thermal behavior and structural evolution by means of TG-FTIR analysis. The studies were focused on two classes of layered precursors, actually distinguished only by the nature of the divalent metal ions, in order to correlate the influence of the clay structure with the thermal behavior of the silver-anionic clay ensembles. The understanding of the thermal degradation mechanism, which is essential to advance the potential applications, requires supplementary characterization techniques such as XRD and FTIR analyses. The thermal analysis performed at three different heating rates revealed the three thermal degradation stages typical for LDHs structure, but different from sample to sample as a consequence of the different interactions between the clay layers and the interlayer anions. The interpretation of the 3D FTIR spectra of the gaseous species resulting in each stage of the thermal degradation process, by means of standard IR spectra, indicates CO₂ and H₂O as main evolved gasses. Moreover, the evolution curves of the gaseous species released by the thermal degradation in air of the studied anionic clays point out that the two gaseous components are eliminated into the temperature ranges corresponding to those given by TG–DTG. The comparative study of the silver-LDH ensembles from the perspective of the structural evolution during the controlled heating suggest a better response from the ensemble with structure consisting of magnesium as divalent cation in the clay network, meaning a better thermal stability.     

Anion induced capsular self-assemblies

Researchers world-wide have employed diverse strategies to achieve various anion binding hosts and anion induced supramolecular architectures due to the increasing appreciation of anion receptor chemistry. Intellectual discovery of molecular capsules for the recognition of different guest species has opened up a new field of research in the area of supramolecular chemistry. This feature article aims to provide an overview of the current status and recent achievements made by us and others in the last decade in the area of anion induced construction of supramolecular capsules and anion binding in molecular capsules.     

Remembrances of self-assemblies past

Research on four types of self-assemblies (micelles, coacervates, gels, and vesicles) is discussed via a particular investigative methodology (in order of appearance): kinetics, dynamic NMR, PGSE-NMR, double-(13)C labeling, molecular dynamics computations, phase diagrams, cryo-HRSEM, rheology, light/electron microscopy, electrophoretic mobility, electroformation, confocal microscopy, and calorimetry. The emphasis here is on how a given method, each in its own special way, illuminates a complex system.     

Hydrogen-bonded self-assemblies in a polychlorotriphenylmethyl radical derivative substituted with six meta-carboxylic acid groups

The synthesis, self assembly and magnetic properties of a polychlorotriphenylmethyl radical, substituted with six meta-carboxylic groups, are reported showing that radical-radical hydrogen bonds in the solid state yield to very weak intermolecular ferromagnetic interactions.     

Free three-dimensional carborane carbanions

Carbon atom functionalization via generation of carbanions is the cornerstone of carborane chemistry. In this work, we report the synthesis and structural characterization of free ortho-carboranyl [C₂B₁₀H₁₁]⁻, a three-dimensional inorganic analog of the elusive phenyl anion that features a “naked” carbanion center. The first example of a stable, discrete C(H)-deprotonated carborane anion was isolated as a completely separated ion pair with a crown ether-encapsulated potassium cation. An analogous approach led to the isolation and structural characterization of a doubly deprotonated 1,1′-bis(o-carborane) anion [C₂B₁₀H₁₀]₂²⁻, which is the first example of a discrete molecular dicarbanion. These reactive carbanions are key intermediates in carbon vertex chemistry of carborane clusters.

Free three-dimensional carborane carbanions, which are inorganic siblings of deprotonated aryls with the “naked” anionic carbon atom are reported.     

Coordination-driven self-organization of switchable [2]rotaxane

A bistable porphyrin-containing [2]rotaxane is synthesized with a shuttling benzylic-amide macrocycle mechanically locked onto the thread subunit by formations of H-bonds with two potential stations. This macrocycle comprises two pyridine groups, which would be easily coordinated with zinc porphyrin. The Zn(II) coordination of porphyrin moiety on the thread subunit, immediately followed by the coordination with pyridine groups on the macrocycle, leads to an intermolecular axle-macrocycle-type nanostructure. Moreover, the self-assembly way shows great difference from the two states of the rotaxane monomer: The coordination-driven self-organization of the trans-state E2 leads to a network structure, whereas the cis-state Z2 gives birth to an irregular assembly.     

A stable N-heterocyclic carbene with a diboron backbone

The synthesis of a novel five-membered inorganic ring, a stable N-heterocyclic carbene with a diboron backbone, is reported. A pentacarbonyltungsten complex containing the new carbene is also described. Spectroscopic evidence indicates that the sterically encumbered carbene is a better sigma-donor than classical N-heterocyclic analogues, demonstrating the significant influence of the inorganic backbone on the coordinating properties of the carbon ligand. Crystal structures have been determined for an iminium precursor, the free carbene, and the tungsten complex.     

Amino acid-bearing ROMP polymers with a stereoregular backbone

The ruthenium-catalyzed ring-opening polymerization (ROMP) of 1-cyclobutenecarbonyl glycine methyl ester provides translationally invariant, head-to-tail ordered polymers. This polybutadiene backbone contains (within the limits of detection) only E-trisubstituted olefins, and it has no stereocenters that would serve as a source of structural ambiguities. Characterization of the polymer products indicates that they have polydispersities ranging from 1.2 to 1.6 and suggests that they are the products of a "living" polymerization. 1-Cyclobutenecarboxamide-derived ROMP polymers are excellent prospects for applications that require stereoregular chains functionalized with polar ligands.