Mechanically Interlocked Chiral Self-Templated [2]Catenanes from 2,6-Bis(1,2,3-triazol-4-yl)pyridine (btp) Ligands

Single-ion magnetism in novel Btp-based cobalt complexes of different charge

The magnetic behavior of single-ion metal complexes may be influenced by the nature and composition of the secondary coordination sphere that can be composed of solvent molecules and counterions bound through non-covalent interactions. However, achieving precise control over the outer-coordination sphere of these magnetic complexes to demonstrate its influence on their magnetic properties presents a challenge. A strategy for varying the number of counterions, while simultaneously preserving the arrangement of the ligand atoms around the metal center without altering its oxidation state, is to adjust the overall formal charge of the complex. This adjustment could lead to changes in the magnetic properties of single-ion metal complexes. In this study, we present two novel ligands featuring the coordinating unit Btp (2,6-bis(1,2,3-triazol-4-yl)pyridine). These ligands are equipped with functional groups that can potentially undergo deprotonation. By carefully selecting the solvents used during the crystallization process of the complexes, we can tune at will the charge of the complexes, thus modifying the composition of the CoII complexes' outer-coordination sphere. We show that, by modifying these conditions, we can tailor the secondary coordination sphere of both charged (mono- and dicationic) and neutral anisotropic CoII metal complexes to show field-induced single-ion magnetism, influencing in turn the size of the barrier to reversal of the magnetization and their slow relaxation process.

A Dualistic Arrangement of a Chiral [1]Rotaxane Based on the Assembly of Two Rings and Two Rods

We demonstrate the synthesis and chiroptical properties of doubled molecules of a chiral [1]rotaxane, based on the assembly of an achiral ring of a phenylacetylene macrocycle (6PAM) and a p-phenylene ethynylene rod. Two molecules of [1]rotaxane constituted the doubled molecule through the ring fusion of 6PAMs to a 10PAM, which assured stationary occupation relative to each optically active unit. The absorption properties of the 10PAM-based doubled molecule and 6PAM-based original unit were consistently characterized by the independent existence of m-phenylene ethynylene ring(s) and p-phenylene ethynylene rod(s). Thus, molar circular dichroism (CD) was directly compared between the doubled molecule (n = 2) and the original unit (n = 1) to show that molar CD was increased more than expected by an increase in the number of units, or by an increase in absorbance. Due to the invariance of the configuration and the relative occupation of two units arranged adjacent to each other in 10PAM, one more comparison was available with an isomeric molecule of two rings and two rods in a threaded-and-unthreaded form. The additional arrangement of an optically inactive unit in an unthreaded form also led to an increase in molar CD, compared to that of the original chiral unit in a threaded form.

Generating water/MeOH-soluble and luminescent polymers by grafting 2,6-bis(1,2,3-triazol-4-yl)pyridine (btp) ligands onto a poly(ethylene-alt-maleic anhydride) polymer and cross-linking with terbium(III)

The synthesis of two new polymers made from P(E-alt-MA) (poly(ethylene-alt-maleic anhydride) and possessing 2,6-bis(1,2,3-triazol-4-yl)pyridine (btp) ligand side chains in 3 and 6 mol%, respectively (P1 and P2, respectively) is described. These polymers were shown to be soluble in MeOH solution and, in the case of P1, also in water, while P2 needed prolonged heating to enable water dissolution. Btp ligands are known for coordinating both d- and f-metal ions and so, herein, we demonstrate by using both UV-Vis absorption, fluorescence emission, as well as time-gated phosphorescence spectroscopies, that both P1 and P2 can bind to Tb(III) ions to give rise to luminescent polymers. From the analysis of the titration data, which demonstrated large changes in the emission intensity properties of the polymer upon Tb(III) binding (ground state changes were also clearly observed, with the absorption being red-shifted at lower energy), we show that the dominant stoichiometry in solution is 1 : 2 (M : L; Tb(III) : btp ratio) which implies that two btp ligands from the polymer background are able to crosslink through lanthanide coordination and that the backbone of the polymer is very likely to aid in coordinating the ions.

Supramolecular chemistry of two new bis(1,2,3-triazolyl)pyridine macrocycles: metal complexation, self-assembly and anion binding

Two new macrocycles containing the bis(1,2,3-triazolyl)pyridine (btp) motif were prepared in high yields from a btp diazide precursor (1). Solution ¹H NMR studies show that this diazide undergoes self-assembly with divalent transition metal ions to form ML₂ complexes with pendant azide groups, apparently suitable for conversion into metal-templated catenanes; however attempts to form these catenanes were unsuccessful. Instead a new macrocycle containing two btp motifs was prepared, which forms a nanotube structure in the solid state. Reduction of the azide groups to amines followed by amide bond formation was used to convert 1 into macrocycle 8 containing btp and isophthalamide functionalities. This macrocycle binds halide and oxalate anions in acetonitrile solely through the isophthalamide motif, and binds aromatic dicarboxylates very strongly through both the isophthalamide amide donors and the btp triazole donors. The macrocycle was complexed with Pd(II) and the resulting complexes were shown to bind strongly to halide anions. The solid state structures of [Pd·8·X]BF₄ (X = Cl^-, Br^-, I^-) were investigated by X-ray crystallography, which showed that [Pd·8·Br] forms an unusual "chain of dimers" structure assembled by metal complexation, N-H⋯Br^- hydrogen bonding and short Pd⋯Pd contacts.

Macrocyclic vs. [2]catenane btp structures: influence of (aryl) substitution on the self templation of btp ligands in macrocyclic synthesis

The synthesis of four 2,6-bis(1,2,3-triazol-4-yl)pyridine (btp) olefin based ligands 3, 4, 11 and 12 is described and their attempted use to form mechanically interlocked molecules using ring closing metatheses (RCM) reactions. The btp ligands were modified in two ways, in 3 and 4 the aryl substitution pattern was changed from 4^th position to 3^rd position and in the case of 11 and 12, the arms were replaced with aliphatic chains. Our study demonstrates that for all four ligands, the RCM reactions only result in the formation of macrocyclic structures, which in three of the cases, were structurally characterised in both solution (using NMR and HRMS) and in the solid-state using X-ray crystallography. NMR studies were also carried out to investigate if these ligands could preorganise in solution via hydrogen bonding interactions. This study provides a handle of how such precursor substitution can be used to direct the formation of macrocycles or mechanically interlocked structures.

Mechanically Interlocked Chiral Self-Templated [2]Catenanes from 2,6-Bis(1,2,3-triazol-4-yl)pyridine (btp) Ligands

We report the efficient self-templated formation of optically active 2,6-bis(1,2,3-triazol-4-yl)pyridine (btp) derived homocircuit [2]catenane enantiomers. This represents the first example of the enantiopure formation of chiral btp homocircuit [2]catenanes from starting materials consisting of a classical chiral element; X-ray diffraction crystallography enabled the structural characterization of the [2]catenane. The self-assembly reaction was monitored closely in solution facilitating the characterization of the pseudo-rotaxane reaction intermediate prior to mechanically interlocking the pre-organised system via ring-closing metathesis.