Self-Sorting in the Formation of Metal–Organic Nanotubes: A Crucial Role of 2D Cooperative Interactions

Macroscopic Helical Assembly of One-Dimensional Coordination Polymers: Helicity Inversion Triggered by Solvent Isomerism

Assembling macroscopic helices with controllable chirality and understanding their formation mechanism are highly desirable but challenging tasks for artificial systems, especially coordination polymers. Here, we utilize solvents as an effective tool to induce the formation of macroscopic helices of chiral coordination polymers (CPs) and manipulate their helical sense. We chose the Ni/R-,S-BrpempH2 system with a one-dimensional tubular structure, where R-,S-BrpempH2 stands for R-,S-(1-(4-bromophenyl)ethylaminomethylphosphonic acid). The morphology of the self-assemblies can be controlled by varying the cosolvent in water, resulting in the formation of twisted ribbons of R-,S-Ni(Brpemp)(H2O)·H2O (R-,S-2T) in pure H2O; needle-like crystals of R-,S-Ni(Brpemp)(H2O)2·1/3CH3CN (R-,S-1C) in 20 vol % CH3CN/H2O; nanofibers of R-,S-Ni(Brpemp)(H2O)·H2O (R-,S-3F) in 20-40 vol % methanol/H2O or ethanol/H2O; and superhelices of R-,S-Ni(Brpemp)(H2O)·H2O (R-,S-4H or 5H) in 40 vol % propanol/H2O. Interestingly, the helicity of the superhelix can be controlled by using a propanol isomer in water. For the Ni/R-BrpempH2 system, a left-handed superhelix of R-4H(M) was obtained in 40 vol % NPA/H2O, while a right-handed superhelix of R-5H(P) was isolated in 40 vol % IPA/H2O. These results were rationalized by theoretical calculations. Adsorption studies revealed the chiral recognition behavior of these compounds. This work may contribute to the development of chiral CPs with a macroscopic helical morphology and interesting functionalities.

Regimented Charge Transport Phenomena in Semiconductive Self-Assembled Rhenium Nanotubes

Photoconductivity, a crucial property, determines the potential of semiconductor materials for use in optoelectronic and photocatalytic device applications. The one-dimensional metal-organic nanotube semiconducting material [{Re(CO)₃}₆(bho)(phpy)₆]_n (MBT 1, where bho is benzene-1,2,3,4,5,6-hexaoate and phpy is 4-phenylpyridine) reported herein exhibits record photocurrent responses at a broad spectral range. MBT 1 is comprised of a unique nanotube structure that is composed of six rhenium sites, six 4-phenylpyridine ligands, and a benzene-1,2,3,4,5,6-hexaoate unit. The highly organized self-assembled molecular bamboo tube MBT 1 displays semiconducting characteristics with a low activation energy of 1.63 meV. The alternating current (AC) and direct current (DC) conductivities of pellet devices are approximately 10^-4 S/cm. For a single-crystal device, DC conductivity was found to be 1.5 S/cm, an unprecedented 10 000 times higher. The bandgap of MBT 1 was determined to be 1.03 eV, consistent with the theoretically estimated value of 1.2 eV. Theoretical calculations suggest that the unique structural architecture of MBT 1 allows for effective charge transport, which is facilitated by the spatial separation of electrons and holes that MBT 1 contains. This also eliminates fast charge recombination. The findings are not only chemically and fundamentally important but also have great potential for applications in innovative nano-optoelectronics.

Chiral nanotubes self-assembled from discrete non-covalent macrocycles

Many strategies have been used to construct supramolecular hollow tubes, including helical folding of oligomers, bundling of rod-like structures, rolling-up of sheets and stacking of covalent cycles. On the other hand, controlling chirality at the supramolecular level continues attracting much interest because of its implications in future applications of porous systems. This review article covers the main examples in the literature that use simple molecular structures as chiral units for precise assembly into discrete non-covalent cyclic structures that are able to form chiral supramolecular tubular systems.

Conformational Regulation of Multivalent Terpyridine Ligands for Self-Assembly of Heteroleptic Metallo-Supramolecules

A two-ligand system composed of the predesigned multivalent and complementary terpyridine-based ligands was exploited to construct heteroleptic metallo-supramolecules and to investigate the self-assembly mechanism. Molecular stellation of the trimeric hexagon [Cd₆L²₃] gave rise to the exclusive self-assembly of the star hexagon [Cd₁₈L¹₆L³₃] through complementary ligand pairing between the ditopic and octatopic tectons. To understand how the intermolecular heteroleptic complexation influenced the self-assembly pathway, the star hexagon was truncated into two triangular fragments: [Cd₁₂L¹₃L⁴₃] and [Cd₁₂L¹₃L⁵₃]. In the self-assembly of [Cd₁₂L¹₃L⁴₃], the conformational movements of hexatopic ligand L⁴ could be regulated by L¹ to promote the subsequent coordination event, which was the key step to the successful multicomponent self-assembly. In contrast, the formation of [Cd₁₂L¹₃L⁵₃] was hampered by the geometrically mismatched intermediates.

Metal-organic tube or layered assembly: reversible sheet-to-tube transformation and adaptive recognition

Rational preparation of an adaptive cavity-like enzyme is a great challenge for chemists. Herein, a new self-assembly strategy for the rational preparation of metal-organic tubes with nano-channels has been developed; both 1D metal-organic tube and corresponding 2D layered assemblies can be selectively synthesized driven by different templates; reversible sheet-to-tube transformation can be realized and the key intermediate has been identified. Furthermore, the newly formed nano-channel displays excellent polarity-selectivity for encapsulation of guest molecules, and can be further expanded or contracted through guest-driven adaptive deformation; even induced by very similar guest molecules, the adaptive deformations can also be obviously distinguished. Finally, the key chemicals benzene/hexane with a similar size can also be effectively separated by such nano-channels in the liquid phase. Our work not only provides a new synthetic strategy for the rational synthesis of metal-organic tubes with a reversible sheet-to-tube transformation character, but also gives a potential method for the construction of adaptive host-like enzymes and an in-depth understanding of the nature of adaptive host and guest molecules.

Visible-Light-Promoted C2 Selective Arylation of Quinoline and Pyridine N-Oxides with Diaryliodonium Tetrafluoroborate

A protocol of visible-light-promoted C2 selective arylation of quinoline and pyridine N-oxides, with diaryliodonium tetrafluoroborate as an arylation reagent, using eosin Y as a photocatalyst for the construction of N-heterobiaryls was presented. This methodology provided an efficient way for the synthesis of 2-aryl-substituted quinoline and pyridine N-oxides. This strategy has the following advantages: specific regioselectivity, simple operation, good functional group tolerance, and high to moderate yields under mild conditions.

Synthesis and Characterization of Ferrocene Based Hemicages

We present a series of tripodal ligands L1-3, which fold into hemicages C1-3 by using coordination-driven dynamic combinational chemistry. The identities of these hemicages were characterized using ¹H NMR, ¹H-¹H COSY, DOSY, and ESI-TWIM-MS. Free rotation of the ferrocene structural units in the ligands affords an adaptable directionality, which is essential for the construction of these hemicages. Encapsulation of adamantane by C2 indicates the presence of a well-defined inner cavity as the binding pocket.

Quantified structural speciation in self-sorted CoII6L4 cage systems

The molecular components of biological systems self-sort in different ways to function cooperatively and to avoid interfering with each other. Understanding the driving forces behind these different sorting modes enables progressively more complex self-assembling synthetic systems to be designed. Here we show that subtle ligand differences engender distinct M₆L₄ cage geometries - an S₄-symmetric scalenohedron, or pseudo-octahedra having T point symmetry. When two different ligands were simultaneously employed during self-assembly, a mixture of homo- and heteroleptic cages was generated. Each set of product structures represents a unique sorting regime: biases toward specific geometries, preferential incorporation of one ligand over another, and the amplification of homoleptic products were all observed. The ligands' geometries, electronic properties, and flexibility were found to influence the sorting regime adopted, together with templation effects. A new method of using mass spectrometry to quantitatively analyse mixtures of self-sorted assemblies was developed to assess individual outcomes. Product distributions in complex, dynamic mixtures were thus quantified by non-chromatographic methods.

Chiral Supramolecular Gels with Lanthanide Ions: Correlation between Luminescence and Helical Pitch

We report the correlation between the fluorescence intensity and the helical pitch of supramolecular hydrogels with Tb(III) and Eu(III) as well as their inkjet printing patterning as an application. The luminescent gels, which exhibited three different emissions of red, green, and blue, could be prepared without and with Eu(III) and Tb(III). The luminescence intensity of supramolecular gels (gel-Tb and gel-Eu) composed of Tb(III) and Eu(III) was ca. 3-fold larger than that of the sol (1+Tb(III) or 1+Eu(III)), which was attributed to large tilting angles between molecules. By AFM observations, these gels showed well-defined right-handed helical nanofibers formed by coordination bonds in which the helical pitch lengths were strongly dependent on the concentrations of lanthanide ions. In particular, the large luminescence intensity of gel-Tb exhibited a smaller helical pitch length than that of gel-1 due to relatively weak π-π stacking with large tilting angles between molecules. The luminescence intensities were enhanced linearly with increasing concentrations of lanthanide ions. This is the first example of the correlation between the helical pitch length and the luminescence intensity of supramolecular materials. The coordination bonding in supramolecular hydrogels had a strong influence on rheological properties. We also developed a water-compatible inkjet printing system to generate luminescent supramolecular gels on A4-sized paper. The images of a logo and the text were composed of three different emissions and were well-printed on A4 sized paper coated with gel-1.