Dynamic and solid-state behaviour of bromoisotrianglimine

Solid-state materials formed from discrete imine macrocycles have potential in industrial separations, but dynamic behaviour during both synthesis and crystallisation makes them challenging to exploit. Here, we explore opportunities for structural control by investigating the dynamic nature of a C-5 brominated isotrianglimine in solution and under crystallisation conditions. In solution, the equilibrium between the [3 + 3] and the less reported [2 + 2] macrocycle was investigated, and both macrocycles were fully characterised. Solvent templating during crystallisation was used to form new packing motifs for the [3 + 3] macrocycle and a previously unreported [4 + 4] macrocycle. Finally, chiral self-sorting was used to demonstrate how crystallisation conditions can not only influence packing arrangements but also shift the macrocycle equilibrium to yield new structures. This work thus exemplifies three strategies for exploiting dynamic behaviour to form isotrianglimine materials, and highlights the importance of understanding the dynamic behaviour of a system when designing and crystallising functional materials formed using dynamic covalent chemistry.

Unravelling Structural Dynamics, Supramolecular Behavior, and Chiroptical Properties of Enantiomerically Pure Macrocyclic Tertiary Ureas and Thioureas

The introduction of urea or thiourea functionality to the macrocycle skeleton represents an alternative way to control conformational dynamics of chiral, polyamines of a figure-shaped periodical structure. Formally highly symmetrical, these macrocycles may adapt diverse conformations, depending on the nature of an amide linker and on a substitution pattern within the aromatic units. The type of heteroatom X in the N-C(═X)-N units present in each vertex of the macrocycle core constitutes the main factor determining the chiroptical properties. In contrast to the urea-containing derivatives, the electronic circular dichroism of thioureas is controlled by the chiral neighborhood closest to the chromophore. The dynamically induced exciton couplet is observed when the biphenyl chromophores are present in the macrocycle core. In the solid state, the seemingly disordered molecules may create ordered networks stabilized by intermolecular S···halogen, H···halogen, and S···H interactions. The presence of two bromine substituents in each aromatic unit in thiourea-derived trianglamine gives rise to a self-sorting phenomenon in the crystal. In solution, this particular macrocycle exists as a dynamic equimolar mixture of two conformational diastereoisomers, differing in the spatial (clockwise and counter clockwise) arrangement of the C-Br bonds. In the crystal lattice, macrocycles of a given handedness assemble into homohelical layers.

Preparation of chiral stationary phase based on a [3+3] chiral polyimine macrocycle by thiol-ene click chemistry for enantioseparation in normal-phase and reversed-phase high performance liquid chromatography

Polyimine macrocycles are a new class of organic macrocycles with cyclic structures, well-defined molecular cavities, and multiple cooperative binding sites, which have recently aroused considerable research interest in molecular recognition and separation. Herein, we report the bonding of a [3+3] chiral polyimine macrocycle (H₃L, C₇₈H₇₈N₆O₃) on thiol-functionalized silica gel using thiol-ene click chemistry to prepare a chiral stationary phase (CSP) for high performance liquid chromatography (HPLC). The fabricated column exhibited excellent chiral separation capability under both normal-phase and reversed-phase conditions. Fourteen and 10 racemates were well resolved on the column in normal-phase mode (using n-hexane/isopropanol as the mobile phase) and reversed-phase mode (using methanol/water as the mobile phase), respectively, including alcohols, esters, ethers, ketones, aldehydes, epoxides and organic acids. Moreover, the column also shows good selectivity toward positional isomers. Six positional isomers (dinitrobenzene, chloroaniline, bromoaniline, iodoaniline, nitrobrobenzene and nitrochlorobenzene) were well separated on the column. In addition, the effects of the injection mass and mobile phase composition on the separation were investigated. The column shows good reproducibility and stability after multiple injections with the relative standard deviation (RSD) (n = 5) of the retention time and resolution being < 0.96 % and 0.65 %, respectively. This study indicates that this type of chiral polyimine macrocycles is a promising chiral selector for HPLC enantioseparation and will push forward the applications of more novel chiral macrocycles for chiral chromatographic separation.

Specific Noncovalent Association of Truncated exo-Functionalized Triangular Homochiral Isotrianglimines through Head-to-Head, Tail-to-Tail, and Honeycomb Supramolecular Motifs

Chiral isotrianglimines were synthesized by the [3 + 3] cyclocondensation of (R,R)-1,2-diaminocyclohexane with C5-substituted isophthalaldehyde derivatives. The substituent's steric and electronic demands and the guest molecules' nature have affected the conformation of individual macrocycles and their propensity to form supramolecular architectures. In the crystal, the formation of a honeycomb-like packing arrangement of the simplest isotrianglimine was promoted by the presence of toluene or para-xylene molecules. A less symmetrical solvent molecule might force this arrangement to change. Polar substituents present in the macrocycle skeleton have enforced the self-association of isotrianglimines in the form of tail-to-tail dimers. These dimers could be further arranged in higher-order structures of the head-to-head type, which were held together by the solvent molecules. Non-associating isotrianglimine formed a container that accommodated acetonitrile molecules in its cavity. The calculated dimerization energies have indicated a strong preference for the formation of tail-to-tail dimers over those of the capsule type.

Sorting Phenomena and Chirality Transfer in Fluoride-Bridged Macrocyclic Rare Earth Complexes

The reaction of fluoride anions with mononuclear lanthanide(III) and yttrium(III) hexaaza-macrocyclic complexes results in the formation of dinuclear fluoride-bridged complexes. As indicated by X-ray crystal structures, in these complexes two metal ions bound by the macrocycles are linked by two or three bridging fluoride anions, depending on the type of the macrocycle. In the case of the chiral hexaaza-macrocycle L1 derived from trans-1,2-diaminocyclohexane, the formation of these μ2-fluorido dinuclear complexes is accompanied by enantiomeric self-recognition of macrocyclic units. In contrast, this kind of recognition is not observed in the case of complexes of the chiral macrocycle L2 derived from 1,2-diphenylethylenediamine. The reaction of fluoride with a mixture of mononuclear complexes of L1 and L2, containing two different Ln(III) ions, results in narcissistic sorting of macrocyclic units. Conversely, a similar reaction involving mononuclear complexes of L1 and complexes of achiral macrocycle L3 based on ethylenediamine results in sociable sorting of macrocyclic units and preferable formation of heterodinuclear complexes. In addition, formation of these heterodinuclear complexes is accompanied by chirality transfer from the chiral macrocycle L1 to the achiral macrocycle L3 as indicated by CPL and CD spectra.

Chiral Self-sorting of Giant Cubic [8+12] Salicylimine Cage Compounds

Chiral self-sorting is intricately connected to the complicated chiral processes observed in nature and no artificial systems of comparably complexity have been generated by chemists. However, only a few examples of purely organic molecules have been reported so far, where the self-sorting process could be controlled. Herein, we describe the chiral self-sorting of large cubic [8+12] salicylimine cage compounds based on a chiral TBTQ precursor. Out of 23 possible cage isomers only the enantiopure and a meso cage were observed to be formed, which have been unambiguously characterized by single crystal X-ray diffraction. Furthermore, by careful choice of solvent the formation of meso cage could be controlled. With internal diameters of din =3.3-3.5 nm these cages are among the largest organic cage compounds characterized and show very high specific surface areas up to approx. 1500 m2  g-1 after desolvation.

Remarkable self-sorting selectivity in covalently linked homochiral and heterochiral pairs driven by Pd2L4 helicate formation

Imidazole-based ditopic ligands bearing two chiral alkyl groups (LRR, LSS, and LRS) were synthesized. The ligands formed Pd2L4 helicates with palladium ions (Pd2+). Self-sorting occurred between LRR and LRS to form (Pd2+)2(LRR)4 and (Pd2+)2(LRS)4 homoligand assemblies, whereas mixing of LRR and LSS with Pd2+ gave a near statistical mixture.

Chirality transfer between hexaazamacrocycles in heterodinuclear rare earth complexes

Both the chiral hexaazamacrocyle L1 based on trans-1,2-diaminocyclohexane and the achiral hexaazamacrocyle L2 based on ethylenediamine form lanthanide(iii) dinuclear μ-hydroxo bridged complexes which have been characterized by NMR and CD spectroscopy. The homodinuclear complexes of the type [Ln₂(L1)₂(μ-OH)₂](NO₃)₄ (Ln = Nd^III, Eu^III, Tb^III and Yb^III) have been synthesized in the enantiopure form and the X-ray crystal structures of Nd^III, Eu^III and Yb^III derivatives have been determined. The heterodinuclear cationic complexes [Ln(L1)Ln'(L2)(μ-OH)₂X₂]ⁿ⁺ have been generated and characterized in solution by using the mononuclear complexes of L1 and L2 as substrates. While the formation of [LnLn'(L1)₂(μ-OH)₂X₂]ⁿ⁺ dinuclear complexes is accompanied by chiral narcissistic self-sorting, the formation of [Ln(L1)Ln'(L2)(μ-OH)₂X₂]ⁿ⁺ dinuclear complexes is accompanied by the sizable sociable self-sorting of macrocyclic units. The homodinuclear complexes [Y₂(L1)₂(μ-OH)₂X₂]ⁿ⁺ and [Ln₂(L2)₂(μ-OH)₂X₂]ⁿ⁺ (Ln = Dy^III, Pr^III and Nd^III) are CD silent in the visible region due to the lack of f-f transitions and the presence of an achiral ligand, respectively. In contrast, the heterodinuclear [Y(L1^S)Ln(L2)(μ-OH)₂X₂]ⁿ⁺ complexes give rise to CD signals arising from the f-f transitions because of the chirality transfer from the L1 macrocyclic unit to the L2 macrocyclic unit.

Mixed Macrocycles Derived from 2,6-Diformylpyridine and Opposite Enantiomers of trans-1,2-Diaminocyclopentane and trans-1,2-Diaminocyclohexane

The condensation reaction of 2,6-diformylpyridine with an equimolar mixture of opposite enantiomers of trans-1,2-diaminocyclopentane and trans-1,2-diaminocyclohexane using a dynamic combinatorial chemistry approach has been examined. In nonmetal-templated reactions, depending on reaction conditions, mixed 2 + 1 + 1 macrocyclic imine or bigger mixed 4 + 2 + 2 imine macrocycle are formed selectively. The 2 + 1 + 1 imine used as a precursor in the templated by Cd^II ions produces a library of enlarged chiral mixed imines coordinated with metal cations among which the hexanuclear Cd^II complex of 6 + 3 + 3 imine was isolated and characterized. All macrocyclic imine compounds have been reduced to the corresponding macrocyclic amines, which have been further transformed into their hydrochlorides. Each macrocyclic compound has been obtained as two enantiomers. For imine macrocycles and for the hydrochloride derivatives of macrocyclic amines, their X-ray crystal structures have been determined. In particular, the crystals of protonated 4 + 2 + 2 macrocyclic amine, which contains two types of diastereomeric cations differing in terms of inverted twists of pyridine moieties, and hexanuclear Cd^II complex of 6 + 3 + 3 imine, which gives a deeper insight into the expansion reaction, have been investigated. A heterochiral self-sorting of 2 + 2 and 2 + 1 + 1 macrocyclic imines has been confirmed by a competition reaction of 2,6-diformylpyridine, racemic trans-1,2-diaminocyclopentane, and racemic trans-1,2-diaminocyclohexane and theoretical calculations.

Temperature-controlled repeatable scrambling and induced-sorting of building blocks between cubic assemblies

Separation of a homogeneous mixture of different components to reach an ordered out-of-equilibrium state in solution has attracted continuous attention. While this can be achieved using external chemical fuels or photo energy, an alternative energy source is heat. Here we realize a temperature-controlled cycle of transitions between ordered and disordered states based on a mixture of two kinds of building blocks that self-assemble into cubic structures (nanocubes). An almost statistical mixture of nanocubes (disordered state) is thermodynamically most stable at lower temperature (25 °C), while homoleptic assemblies composed of single components are preferentially produced at higher temperature (100 °C) followed by rapid cooling. The scrambling of the building blocks between the nanocubes takes place through the exchange of free building blocks dissociated from the nanocubes. Based on this mechanism, it is possible to accelerate, retard, and perfectly block the scrambling by the guest molecules encapsulated in the nanocubes.

In this paper, the authors study the temperature-controlled dynamic behavior of a system of nanocubes self-assembled from two different building blocks. Non-intuitively, the disordered, equilibrium state (a mixture of heteroleptic cubes) and the ordered, out-of-equilibrium state (a mixture of homoleptic cubes) are cycled by heating and subsequent rapid cooling.

Sterically Crowded Trianglimines-Synthesis, Structure, Solid-State Self-Assembly, and Unexpected Chiroptical Properties

The chiral, triangular-shape hexaimine macrocycles (trianglimines), bearing bulky alkynyl or aryl substituents were synthesized and studied by means of experimental and theoretical methods. The macrocyclization reactions are driven by the extraordinary stability of the trianglimine ring and provided products with high yields. Electrostatic repulsion between imine nitrogen atoms and the substituents forced an anti conformation of the aromatic linkers. Although the DFT-optimized structure of 7 is D₃ symmetrical, in the crystal, the macrocycle adopts a bowl-like molecular shape. The macrocycle self-assembles into tail-to-tail dimers by mutual interdigitation of aromatic moieties. In contrast, macrocycle 8 adopts a rigid pillararene-like conformation. The nature of the substituent significantly affects the electronic properties of the linker. As a result, unexpectedly high exciton Cotton effects are observed in the electronic circular dichroism (ECD) spectra. The origin of these effects was subject of an in-depth study.

One-step Access to Resorcinsalens-Solvent-Dependent Synthesis, Tautomerism, Self-sorting and Supramolecular Architectures of Chiral Polyimine Analogues of Resorcinarene

Substituted 2,4- and 4,6-dihydroxyisophthalaldehydes were condensed with optically pure and racemic trans-1,2-diaminocyclohexane to form resorcinarene-like polyimine macrocycles (resorcinsalens), the structure and stoichiometry of which were controlled by the choice of the reaction medium. Particularly, the cyclocondensation reactions were driven by the solubility, tautomerization, or by social self-sorting. The resorcinsalens crystallized as inclusion compounds, in which the guest molecules were situated either in channels or in voids. In the highly hydrated crystals of one of the [2+2] macrocycles and chloroform-solvated crystals of a [4+4] product the channels were interconnected, as in zeolites, enabling possible migration of loosely bound solvent molecules in three dimensions. The association mode depended on the structural modification of the host molecule and the type of included solvent molecule(s).

Narcissistic chiral self-sorting of molecular face-rotating polyhedra

Narcissistic chiral self-sorting prevailed in the assembly of molecular face-rotating polyhedra from a C_3h building block 5,5,10,10,15,15-hexabutyl-truxene-2,7,12-tricarbaldehyde and racemic mixtures of 1,2-diamines.

Consistent supramolecular assembly arising from a mixture of components – self-sorting and solid solutions of chiral oxygenated trianglimines

The formation of trianglimines and their aggregates is stereoselective, and uniformly chiral macrocycles differing in chemical composition crystallize as solid solutions.

Making a Right or Left Choice: Chiral Self-Sorting as a Tool for the Formation of Discrete Complex Structures

This review discusses chiral self-sorting-the process of choosing an interaction partner with a given chirality from a complex mixture of many possible racemic partners. Chiral self-sorting (also known as chiral self-recognition or chiral self-discrimination) is fundamental for creating functional structures in nature and in the world of chemistry because interactions between molecules of the same or the opposite chirality are characterized by different interaction energies and intrinsically different resulting structures. However, due to the similarity between recognition sites of enantiomers and common conformational lability, high fidelity homochiral or heterochiral self-sorting poses a substantial challenge. Chiral self-sorting occurs among natural and synthetic molecules that leads to the amplification of discrete species. The review covers a variety of complex self-assembled structures ranging from aggregates made of natural and racemic peptides and DNA, through artificial functional receptors, macrocyles, and cages to catalytically active metal complexes and helix mimics. The examples involve a plethora of reversible interactions: electrostatic interactions, π-π stacking, hydrogen bonds, coordination bonds, and dynamic covalent bonds. A generalized view of the examples collected from different fields allows us to suggest suitable geometric models that enable a rationalization of the observed experimental preferences and establishment of the rules that can facilitate further design.

Unexpected formation of a tubular architecture by optically active pure organic calixsalen

Herein, an unusual tubular formation of a supramolecular organic framework by optically active macrocyclic calixsalen is shown via single crystal X-ray diffraction.

Specific Noncovalent Association of Chiral Large-Ring Hexaimines: Ion Mobility Mass Spectrometry and PM7 Study

Ion mobility mass spectrometry and PM7 semiempirical calculations are effective complementary methods to study gas phase formation of noncovalent complexes from vaselike macrocycles. The specific association of large-ring chiral hexaimines, derived from enantiomerically pure trans-1,2-diaminocyclohexane and various isophthaldehydes, is driven mostly by CH-π and π-π stacking interactions. The isotrianglimine macrocycles are prone to form two types of aggregates: tail-to-tail and head-to-head (capsule) dimers. The stability of the tail-to-tail dimers is affected by the size and electronic properties of the substituents at the C-5 position of the aromatic ring. Electron-withdrawing groups stabilize the aggregate, whereas bulky or electron-donating groups destabilize the complexes.