Double Helicate Research Articles

Infinite Twisted Polycatenanes.

Poly[n]catenanes have exceptional mechanical bonding properties that give them tremendous potential for use in the development of molecular machines and soft materials. Synthesizing these compounds has, however, been proved to be a formidable challenge. In this paper, we describe a concise method for the construction of twisted polycatenanes. Our approach involves using preorganized double helicates as templates, and linked crosswise in a linear fashion by either silver ions or triple bonds. Using this approach, we successfully synthesized twisted polycatenanes with both covalent bonding employing Ag(I) ions and ethynylene units, respectively, as the linkages and leveraging the same Ag(I)-templated double helicate in both cases. Synthesis with Ag(I) ions formed a single-crystalline one-dimensional (1D) coordination poly[n]catenane, and synthesis using ethynylene units generated 1D fibers which self-assembled with solvents to form a gel. Our results confirm the potential of multi-stranded metallohelicates for creating sophisticated mechanically interlocked molecules and polymers, which could pave the way for exploration in the realms of molecular nanotopology and materials design.

Infinite Twisted Polycatenanes

AbstractPoly[n]catenanes have exceptional mechanical bonding properties that give them tremendous potential for use in the development of molecular machines and soft materials. Synthesizing these compounds has, however, proven to be a formidable challenge. Herein, we describe a concise method for the construction of twisted polycatenanes. Our approach involves using preorganized double helicates as templates, linked crosswise in a linear fashion by either silver ions or triple bonds. By using this approach, we successfully synthesized twisted polycatenanes with both coordination and covalent bonding employing Ag(I) ions and ethynylene units, respectively, as the linkages and leveraging the same Ag(I)‐templated double helicate in both cases. Synthesis with Ag(I) ions formed a single‐crystalline one‐dimensional (1D) coordination poly[n]catenane, and synthesis using ethynylene units generated 1D fibers which self‐assembled with solvents to form a gel. Our results confirm the potential of multi‐stranded metallohelicates for creating sophisticated mechanically interlocked molecules and polymers, which could pave the way for exploration in the realms of molecular nanotopology and materials design.

N···I···N]+ Type Halogen-Bonding-Driven Supramolecular Helical Polymers with Modulated Chirality.

The [N···I···N]+ type halogen bond has been utilized to synthesize supramolecular architectures, while the applications in constructing helical motifs and modulating supramolecular chirality have been unexplored so far. In this work, the [N···I···N]+ halogen bond was introduced to drive the formation of supramolecular helical polymers via a Ag(I) coordination intermediate, showing tunable supramolecular chirality. Pyridine segments were conjugated to the asymmetric ferrocene skeleton, which show "open" and "closed" geometry depending on the sp2 N positions. Coordination with Ag(I) generated one-dimensional (1D) double helices and 2D helicates featured the [Ag(O)···I···Ag(O)]+ bond, which further stacked into 3D porous frameworks with chiral channels and adjustable pore sizes. Ionic exchange afforded 1D supramolecular helical polymers in solution phases driven by the [N···I···N]+ type halogen bonds, which was evidenced by the experimental results and density functional theory calculation. Fc2 exclusively demonstrated tunable supramolecular chirality in the formation of coordinated and halogen bonded polymers. In addition, solvent change would further inverse the helicity of halogen bonded supramolecular helical polymers depending on the rotation of the ferrocenyl core whose "closed" and "open" states were accompanied by the breakage of intramolecular hydrogen bonds. This work introduces a [N···I···N]+ type ionic halogen bond to prepare supramolecular helical polymers, providing multiple protocols in regulating helicity by ion exchange and solvent environments.

Synthesis, structural diversity, DFT and luminescence properties of Ni(II), Zn(II) and Cd(II) complexes derived from a 2, 2′-bipyridyl hydrazone Schiff base

A new 2, 2′-bipyridyl hydrazone Schiff base ligand (H2L) was synthesized, and four novel complexes, namely, [Ni2(L2−)2]‧3CH3OH (1), [Zn2(L2−)2]‧DMF‧3H2O (2), [Cd3(H2L)2Cl6(H2O)2]‧2H2O (3), and {[Zn2(L2−)Cl2]‧CH3OH}n (4), were obtained via the solvent evaporation method. The four complexes were structurally investigated by single-crystal X-ray diffraction and additionally characterized by powder X-ray diffraction, infrared spectroscopy and element analysis. X-ray analytical results show that complexes 1 and 2 exhibit dinuclear double helicates with similar structures. Complex 3 exists as a trinuclear structure with two different configurations in the cadmium ions. Complex 4 exists as a one-dimensional coordination polymer with two different configurations in the zinc ions. The diverse architectures of the complexes show that the spacer 2, 2′-bipyridyl ligands and metal ions have significant impacts on the structures and the coordination modes. Furthermore, thermogravimetric analysis, DFT and luminescence properties of the complexes have been investigated, and electrochemical studies for complex 1 were carried out as well.

Supramolecular interactions in a family of dinuclear helicates in the solid-state

ABSTRACT Metallo-helicates are a commonly encountered assembly within supramolecular chemistry. Interest in these architectures stems from their inherent helical chirality which positions them for a diverse range of applications such as catalysis and non-linear optics (NLO). The current study uses Co(II) dinuclear double helicates as versatile supramolecular synthons. The ditopic ligand, L, features two tridentate quinolinyl-hydrazone binding sites imparting it with hydrogen bond donors and π-faces for secondary supramolecular interactions. Incorporation of L into [Co2(L)2]4+ helical assemblies results in a helical cationic supramolecular synthon with moieties predisposed to forming π-π stacking and hydrogen bond interactions. The single-crystal X-ray structures of [Co2(L)2]X4 (X = ClO4 −, BF4 − and CF3SO3 −) revealed a variety of anion dependent hydrogen bond networks arising through the interaction of the hydrazide hydrogen with the anion. These interactions in turn strongly influence the nature of the π-π stacking interactions of the quinoline moieties which can be analysed via the Hirshfield surface.

Simultaneous Generation of a [2 × 2] Grid-Like Complex and a Linear Double Helicate: a Three-Level Self-Sorting Process.

Two constitutional dynamic libraries (CDLs)-each containing two amines, two dialdehydes, and two metal salts-have been found to self-sort, generating two pairs of imine-based metallosupramolecular architectures (sharing no component) each with a [2 × 2] grid-like complex and a linear double helicate. These CDLs provided unique examples of a three-level self-sorting process, as only two imine-based ligand constituents, two metal complexes, and two architectures were selected during their assembly out of all the possible combinations of their initial components. The metallosupramolecular architectures assembled were characterized by NMR, mass spectroscopy, and X-ray crystallography.

Near‐Infrared Circularly Polarized Luminescence through Intramolecular Excimer Formation of Oligo(p‐phenyleneethynylene)‐Based Double Helicates

AbstractInvited for the cover of this issue is the group of Koji Miki, Kouichi Ohe, and colleagues at Kyoto University. The image depicts mythical dragons as carbon‐based double helicates. Read the full text of the article at 10.1002/chem.201901467.

Near-Infrared Circularly Polarized Luminescence through Intramolecular Excimer Formation of Oligo(p-phenyleneethynylene)-Based Double Helicates.

Carbon-based double helicates consisting of two anthracene-containing oligo(p-phenyleneethynylene) units and two flexible chiral 1,1'-binaphthyl units or two rigid chiral 9,9'-spirobifluorene units were developed. The curved oligo(p-phenyleneethynylene) fragments in the double helicates were successfully constructed by tin-mediated reductive aromatization. Helical oligo(p-phenyleneethynylene) double strands fixed by two rigid spirobifluorene units showed little structural change under photoirradiation, thereby emitting circularly polarized luminescence (CPL) in the visible region with a high quantum yield (ΦPL =0.93). In contrast, flexible binaphthyl units induced dynamic structural change of the oligo(p-phenyleneethynylene) luminophores under photoirradiation, leading to strong CPL (|glum |=1.1×10-2 ) in the near-infrared (NIR) region. UV/Vis, circular dichroism (CD), CPL and NMR spectroscopic analyses of the binaphthyl-hinged double helicate suggested excimer formation between two π-conjugated strands in the excited state. Theoretical calculations highlight the importance of the tightly interlocked excimer structure of the carbon-based double helicate in controlling the angle between the electric and magnetic transition dipole moments for strong NIR CPL generation.

Front Cover: Near‐Infrared Circularly Polarized Luminescence through Intramolecular Excimer Formation of Oligo(p‐phenyleneethynylene)‐Based Double Helicates (Chem. Eur. J. 39/2019)

Carbon-based double helicates consisting of oligo(p-phenyleneethynylene)s and “flexible” 2,2’-binaphthyls or “rigid” 9,9′-spirobifluorenes were synthesized. The “rigid” double helicate acts as a bright macrocyclic fluorophore. The “flexible” double helicate forms a tightly interlocked intramolecular excimer under photoirradiation, emitting near-infrared circularly polarized luminescence with high dissymmetry factor value. More information can be found in the Full Paper by K. Miki, K. Ohe, et al. on page 9211.

Construction and interconversion of anion-coordination-based ('aniono') grids and double helicates modulated by counter-cations.

Supramolecular assembly of well-defined discrete architectures has been of great interest due to the tunable properties of these structures in functional materials and bio-mimicking. While metal-coordination-driven assembly has been extensively studied, anion-coordination-driven assembly (ACDA) is just emerging for constructing complex supramolecular structures. Herein two A2n L 2n (A = anion, L = ligand; n = 1 or 2) 'aniono'-supramolecular assemblies, i.e. double helicates and the first anion grid, have been constructed based on the coordination between phosphate (PO4 3-) anion and a bis-tris(urea) ligand. Moreover, the aniono-grid and double helicate motifs can be readily interconverted under ambient conditions by simply changing the counter-cation. These results redefine the power and scope of ACDA, which may represent a new approach in the assembly of well-defined architectures in parallel with the metal coordination-driven assembly of metallo-supramolecules.

Homochiral Double Helicates Based on Cyclooctatetrathiophene: Chiral Self-Sorting with the Intramolecular S⋅⋅⋅N Interaction.

The design and synthesis of homochiral double helicates are reported that are constructed by means of Ag-induced supramolecular self-sorting of saddle-shaped cyclooctatetrathiophene-based pyridine ligands (1 and 2). The intramolecular S⋅⋅⋅N interaction ensures that the thiophene and pyridine rings of ligands 1 and 2 are in coplanar and syn-locked structures. In the presence of Ag+ , the racemic ligands 1 and 2 only afforded homochiral double helicates, indicating effective chiral self-sorting process under the influence of the S⋅⋅⋅N interaction. The X-ray crystal structure of 12 Ag2 reveals a pair of homochiral double helicates (R,R,R,R)-12 Ag2 and (S,S,S,S)-12 Ag2 . Furthermore, chiral resolution of racemic ligand 1 was achieved by chiral-phase HPLC, and the enantiomers and their corresponding enantiopure Ag complexes were characterized.

Self-assembly and peripheral guest-binding of [Zn3L2(H2O)6]6 + triangular double helicate

A novel [Zn3L2(H2O)6]6+ triangular double helicate has been self-assembled by subcomponent C3-symmetric triamine, zinc(II) and 2-formylpyridine. The helicate structure was confirmed by 1H NMR, ESI-Mass and single-crystal X-ray diffraction. The results reveal that this sandwich-like helicate contains only limited central cavity but relatively open peripheral apertures. The latter are subject to bind suitable guest molecules by complementary arrangement. During the host-guest study, it's found the most up field shifts (Δδ=−0.06~−0.20ppm) of 1H signals occurred at the ligand protons near the apertures, where the aromatic rings of guests could fit the grooves of the ligands and offer the electronic perturbation to most nearby hydrogens of the host.

Luminescent Silver-Purine Double Helicate: Synthesis, Self-Assembly and Antibacterial Action.

Invited for this month's cover is the group of Prof. Sandeep Verma from the Indian Institute of Technology Kanpur, India. The cover picture shows the release of silver ions from silver-purine double helicate assembly that exhibits antibacterial activity against Gram-negative bacteria, E. coli. Read the full text of the article at 10.1002/cplu.201600293.

Luminescent Silver-Purine Double Helicate: Synthesis, Self-Assembly and Antibacterial Action.

The synthesis, self-assembly and antibacterial activity of a luminescent silver-purine double helicate is reported. The structure of the newly synthesized silver-supported helicate [C36 H24 N16 O4 Cl5 Ag1 ] was unambiguously characterized by single-crystal X-ray crystallography. It exhibited a bright bluish-green emission (λmax =460 nm), when excited with 380 nm light. Microscopic investigations showed that the complex has a propensity to self-assemble into nanospheres. The antibacterial activity of this silver-containing helicate was studied against both Gram-positive and Gram-negative bacteria. MIC (minimal inhibitory concentration) values showed that the complex is very active against Gram-negative bacteria. Further internalization of the silver complex into E. coli bacteria was mapped with the help of microscopic techniques. These results are significant as silver was recently found to enhance antibiotic action against Gram-negative bacteria, raising hope in countering severe bacterial infections.

Full characterization and cytotoxic activity of new silver(i) and copper(i) helicates with quaterpyridine

DNA binding and cells' cycle disorders caused by four new dinuclear Ag(i) and Cu(i) double helicates with quaterpyridine ligands.

Supramolecular reactions of metallo-architectures: Ag2-double-helicate/Zn4-grid, Pb4-grid/Zn4-grid interconversions, and Ag2-double-helicate fusion.

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).

Synthesis, structure, and spin crossover above room temperature of a mononuclear and related dinuclear double helicate iron(ii) complexes.

A mononuclear iron(ii) complex, [FeII(L1Me)2](PF6)2 (1), and a related dinuclear one, [Fe(L2C2)2](PF6)4·5H2O·MeCN (2), were prepared, where L1Me is a tridentate N3 coordinating Schiff-base ligand, 1-methyl-1,2,3-triazol-4-yl-methylideneamino-2-ethylpyridine, and L2C2 is a dimeric form ligand of L1Me, 1,1'-(1,2-ethanediyl)bis-1,2,3-triazol-4-yl-methylideneamino-2-ethylpyridine, and their magnetostructural relationships were investigated. Mononuclear 1 shows a gradual one-step spin crossover (SCO) from the low-spin (LS) state (S = 0) at room temperature (RT) to the mostly high-spin (HS) state (S = 2) at 470 K spanning a temperature range of more than 170 K, while dinuclear 2 shows an anomalous two-step SCO with a gradual transition in a first step from the LS-LS state at RT to around 432 K and then an abrupt spin transition centred at 432 K with 11 K wide hysteresis in a second step (T1/2↑ = 437 K and T1/2↓ = 426 K) reaching the mostly HS-HS state. Single crystal X-ray structure analyses revealed that the iron(ii) centre of mononuclear 1 has an N6 octahedral coordination environment with two tridentate L1Me ligands, while the complex-cation of 2 has a dinuclear double helicate architecture as though a dimeric form of two complex-cations of 1 replaced their methyl group with a bridging ethylene chain. Both complexes have a cationic two-dimensional (2D) structure in which the 2D layer of mononuclear 1 is constructed of intermolecular CHN hydrogen bonds between adjacent complex-cations, while that of dinuclear 2 is constructed of both intermolecular π-π and CH/π interactions between neighboring helicates.

Homochiral [2]Catenane and Bis[2]catenane from Alleno-Acetylenic Helicates - A Highly Selective Narcissistic Self-Sorting Process.

Homochiral strands of alternating alleno-acetylenes and phenanthroline ligands (P)-1 and (P2)-2, as well as their corresponding enantiomers, selectively assemble with the addition of silver(I) salt to yield dinuclear and trinuclear double helicates, respectively. Upon increasing the solvent polarity, the dinuclear and trinuclear helicates interlock to form a [2]catenane and bis[2]catenane, bearing 14 chirality elements, respectively. The solid-state structure of the [2]catenane reveals a nearly perfect fit of the interlocked strands, and the ECD spectra show a significant amplification of the chiroptical properties upon catenation, indicating stabilization of the helical secondary structure. Highly selective narcissistic self-sorting was demonstrated for a racemic mixture consisting of both short and long alleno-acetylenic strands, highlighting their potential for the preparation of linear catenanes of higher order.

6,6″-Dimethyl-2,2′:6′,2″-terpyridine revisited: New fluorescent silver(I) helicates with in vitro antiproliferative activity via selective nucleoli targeting

6,6″-Dimethyl-2,2′:6′,2″-terpyridine ligand (L) reacts in equimolar ratio with Ag(I) ions what results in formation of dinuclear double helicates, which differ in terms of framework and complexity in accordance to counterions and solvent applied. Obtained complexes were thoroughly studied in terms of their biological activity, with the positive antiproliferative outcome on three human cancer cell lines: human breast cancer (T47D), human cervical carcinoma (HeLa) and human lung cancer (A-549). Performed DNA binding experiments showed that given Ag(I) species specifically interact with DNA double helix via intercalation and were visualized by confocal microscopy to specifically bind to the nuclei. All newly synthesized helical systems exhibit promising antimicrobial activity against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus bacterial strains. Spectrophotometric properties were described as fulfilment of structural studies of newly presented complexes confirming their helical structure in solution.

Tetratopic pyrimidine–hydrazone ligands modified with terminal hydroxymethyl and acryloyl arms and their Pb(ii), Zn(ii), Cu(ii) and Ag(i) complexes

The first tetratopic pyrimidine-hydrazone (pym-hyz) molecular strands containing terminal hydroxymethyl (L1) and acryloyl (L2) functional groups have been synthesised. L1 was produced by step-wise imine condensation reactions, starting with 6-hydroxymethyl-2-pyridinecarboxaldehyde. L2 was then synthesised through the treatment of L1 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 L1 and L2 uncoiled upon reaction with an excess amount of Pb(II), Zn(II) and Cu(II) ions, resulting in linear M4LA8 complexes (where M = Pb(II), Zn(II), or Cu(II); L = L1 or L2; and A = ClO4(-), SO3CF3(-) or BF4(-)). Horse-shoe shaped Pb2LA4 complexes were also formed by reacting Pb(II) ions with either L1 or L2 in a 2 : 1 metal to ligand ratio. The addition of Ag(I) ions to either L1 or L2 resulted in Ag2L2A2 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 Pb4L1A8, horse-shoe shaped Pb2L1(ClO4)4, twisted Cu3L2(SO3CF3)6, and double helicate Ag2L12(SO3CF3)2 complexes yielding the structures [Pb4L1(ClO4)7(H2O)]ClO4·4CH3NO2 (1), [Pb4L1(SO3CF3)8]2·6CH3CN·H2O (2), [Pb2L1(ClO4)2(CH3CN)(H2O)](ClO4)2·2CH3CN·C4H10O·H2O (3), [Cu3L2(SO3CF3)3(CH3CN)2(H2O)](SO3CF3)3·2CH3CN·H2O (4) and [Ag2L12](SO3CF3)2·CH3CN·H2O (5), respectively.