Redox-Responsive Colloidal Particles Based on Coordination Polymers Incorporating Viologen Units

Colloidal particles based on supramolecular polymers are emerging as promising functional materials because of their intrinsic dynamic features and the possibility of stimuli responsivity. In this work, ≈200 nm self-assembled redox-responsive colloidal particles made of 1D-coordination polymers were readily prepared. In these metallopolymers, organic entities made of bis(viologen) groups covalently associated with terpyridine units are spontaneously bridged by Zn²⁺ cations through the formation of coordination bonds. The properties of these particles were analyzed and their redox activities investigated. Upon reduction of the viologen units, the formation of π-dimers between the reduced viologen moieties was demonstrated by spectroscopic experiments. It was shown that intermolecular π-dimers (i.e., between different polymer chains) that do not exist in homogeneous polymer solutions were, nevertheless, formed in the particle's structure because of the effects of confinement. The presence of these π-dimers allows stabilization of the charge in the colloids.

Topotactic desolvation and condensation reactions of 3D Zn3TiF7(H2O)2(taz)3·S (S = 3H2O or C2H5OH)

Thermodiffraction, IR, DFT calculations, and ¹H and ¹⁹F NMR characterizations of the desolvatation and reversible condensation reactions of Zn₃TiF₇(taz)₃ family.

[3]rotaxanes composed of two dibenzo-24-crown-8 ether wheels and an azamacrocyclic complex

The azamacrocyclic complex was used as a platform for the construction of [3]rotaxanes containing two DB24C8 macrocycles per molecule. The complex unit incorporates two electron deficient π-bond systems and two N-H hydrogen bond donating groups which facilitated the formation of a 1 : 2 interlocked structure. Synthesis and properties of such compounds are presented. Structures of the obtained compounds were confirmed by NMR spectroscopy, ESI mass spectrometry, elemental analysis and single crystal X-ray diffraction. Both [3]rotaxanes containing two DB24C8 macrocycles per molecule crystallise in P1[combining macron] and P21/n space groups. They have different counterions (PF6- and Cl- anions, respectively) and mostly disordered solvent molecules such as water, methanol and acetone. Both [3]rotaxanes have a flexible axle in which the Cl- salt takes the shape closer to the "S"-letter, while in the PF6- case the axle is more linear. The shape results from respective packing and intra-, and intermolecular interactions among the moieties in the rotaxane and the crystal lattice.

Redox-Triggered Folding of Self-Assembled Coordination Polymers incorporating Viologen Units

We report the study of stimuli-responsive Zn^II and Fe^II coordination polymers (MC3⁴⁺ or MC2⁴⁺ with M=Fe²⁺ or Zn²⁺ ). These soluble metallopolymers were formed spontaneously by reaction of an organic ligand (C3⁴⁺ or C2⁴⁺ ) with one molar equivalent of metal ions. The C3⁴⁺ and C2⁴⁺ ligands incorporate two chelating terpyridine groups bridged by a redox responsive hinge featuring two viologen units (viologen=N,N'-dialkyl-4,4'-bipyridinium) linked either with propyl (C3⁴⁺ ) or ethyl (C2⁴⁺ ) chains. The viologen units in the polymer chains were reduced (1 e^- per viologen group) either by bulk electrolysis or by visible-light irradiation carried out in the presence of a photosensitizer. The 1 e^- reduction of the viologen units in the MC2⁴⁺ polymers induced a slight decrease in the viscosity of the solutions due to a modification of the overall charge carried by the metallopolymers. In strong contrast, reduction of coordination polymers involving propyl linkers (MC3⁴⁺ ) led to a remarkable increase (≈+400 %) in observed viscosity. This reversible effect was attributed to a folding of the polymer chains triggered by π-dimerization of the photo-generated viologen cation radicals.

Novel 1D coordination polymers built from acyclic cryptate containing bis(1H-1,2,4-triazole) ligands and featuring coordinated counteranions

Two new coordination polymers, namely, ZnL₂(BF₄)₂ (1) and CuL₂(NO₃)₂ (2) were constructed from a new flexible acyclic cryptate-bis(1H-1,2,4-triazole) ligand.

Rotaxanes composed of dibenzo-24-crown-8 and macrocyclic transition metal complexing tetraimine units

New rotaxanes, composed of dibenzo-24-crown-8 and the axle containing two tetraazamacrocyclic Ni and/or Cu units, adopt either folded or extended conformations and di-Ni-rotaxanes exhibit a shuttling effect of DB24C8.

Acid-Base Switchable [2]- and [3]Rotaxane Molecular Shuttles with Benzimidazolium and Bis(pyridinium) Recognition Sites

For the purpose of developing higher level mechanically interlocked molecules (MIMs), such as molecular switches and machines, a new rotaxane system was designed in which both the 1,2-bis(pyridinium)ethane and benzimidazolium recognition templating motifs were combined. These two very different recognition sites were successfully incorporated into [2]rotaxane and [3]rotaxane molecular shuttles which were fully characterized by ¹ H NMR, 2D EXSY, single-crystal X-ray diffraction and VT NMR analysis. By utilizing benzimidazolium as both a recognition site and stoppering group it was possible to create not only an acid/base switchable [2]rotaxane molecular shuttle (energy barrier 20.9 kcal⋅mol^-1 ) but also a [3]rotaxane molecular shuttle that displays unique dynamic behavior involving the simultaneous motion of two macrocyclic wheels on a single dumbbell. This study provides new insights into the design of switchable molecular shuttles. Due to the unique properties of benzimidazoles, such as fluorescence and metal coordination, this new type of molecular shuttle may find further applications in developing functional molecular machines and materials.

Active-template synthesis of “click” [2]rotaxane ligands: self-assembly of mechanically interlocked metallo-supramolecular dimers, macrocycles and oligomers

A "click" active-metal-template strategy has been exploited to develop mono- and bi-2,2′,6′,2″-terpyridine functionalised [2]rotaxanes. When reacted with Fe(ii) ions these rotaxanes formed metallo-bis-([2]rotaxanes), macrocycles and oligomers.

[2]Pseudorotaxanes, [2]rotaxanes and metal-organic rotaxane frameworks containing tetra-substituted dibenzo[24]crown-8 wheels

[2]Pseudorotaxanes, [2]rotaxanes and metal-organic rotaxane framework materials that utilise DB24C8 as the wheel component are well known and structural variations based on changing the axle component are common. Studies in which the DB24C8 wheel is structurally modified are much more limited. Herein, is described the synthesis of symmetrical DB24C8 analogues containing four CH(2)OR (R = CH(2)CH(2)CH(3), CH(2)(C(6)H(5)), C(6)H(5) and C(6)H(4)(4-COOEt)) substituents on the 4 and 5 positions of the aromatic rings. The effect of these molecular appendages on the stability and structures of the interpenetrated and interlocked molecules derived from these new wheels is described. The major effects are an increase in association constants for the formation of [2]pseudorotaxanes relative to DB24C8, the crystal packing of [2]rotaxanes and a change on the internal structure of a 2D MORF (R = C(6)H(5)) compared to DB24C8.