Supramolecular assemblies involving metal organic ring interactions: Heterometallic Cu(II)-Ln(III) two dimensional coordination polymers

Three isostructural two-dimensional coordination polymers of the general formula [Ln2(CuL)3(H2O)9]$5.5H2O, where Ln is La (1), Nd (2), and Gd (3), have been synthesized and isolated from aqueous solutions and their single-crystal structures determined by X-ray diffraction. The supramolecular interaction between the non-aromatic metallorings plays an important role in stabilizing the structure of these compounds. The thermal stability, reversible solvent uptake, electronic properties and magnetic studies of these compounds are also reported

Negatively photochromic organic compounds: Exploring the dark side

The last few years have seen an explosion of interest in traditional photochromic systems not only for their applications in variable transmission devices, which continues to attract commercial interest, but also for the ability of these molecules to undergo structural and electronic reorganisation which has been seized upon by materials scientists for the development of switches, logic gates, photoinduced molecular motions such as rotors and fibrils, and photoregulation of drug availability. This comprehensive review examines, for the first time, the ‘dark side of photochromism’; negatively photochromic systems which are coloured in their ground state and reversibly photobleach upon exposure to electromagnetic radiation with a wavelength over ca. 400 nm i.e. visible light responsive systems. This review is organised by structural class and examines their synthesis, structure, key spectroscopic data for coloured and bleached species, structure – switching relationships and applications. The usefulness of these negatively photochromic systems is only gradually coming to the fore with the advantages of low energy activation c.f. conventional Uv-activated switches, enabling the modulation of a plethora of useful optical and physical properties and the design of new materials with broad ranging applications

Boron-Nitrogen Dative Bonds in Structural Supramolecular Chemistry

This work describes the use of boron-nitrogen dative bonds in supramolecular chemistry. Molecular tectons have been synthesized for crystal engineering. These tectons are linked via B-N dative bonds to form 1-dimensional polymers and macrocycles. B-N dative bonds were further used for the formation of crystalline organic networks by assembly of a tritopic boronate ester with ditopic N-donor ligands. These networks could be structurally characterized by single crystal X-ray diffraction to reveal 2-dimensional polymers. These structures were observed by PXRD to collapse upon removal of solvent. The reaction of a larger triboronate ester with 4,4'-bipyridine resulted in an organogel which formed with as little as 0.5 wt% of the network in toluene. The orange gel exhibited thermochromic properties, with a Tgel of 60 °C. Association constants for the formation of B-N dative bonds between dioxaborole and pyridyl ligands were examined by 1H NMR and ITC titrations. Ka values in excess of 106 M-1 can be obtained by varying the electronics of the reaction partners. The adducts have been characterized comprehensively by single crystal X-ray diffraction. Finally, the dative B-N bond was used for the synthesis of main-chain supramolecular polymers. Self-complementary monomers were synthesized containing a dialkylaminopyridine and a dioxaborole. These monomers assembled in chloroform to form polymers which were characterized by viscosity and DOSY NMR experiments

Supramolecular Assemblies Based on Dative Boron-Nitrogen Bonds

Dative boron nitrogen bonds were found to be a useful binding motif in structural supramolecular chemistry. Crystalline cages were formed using a diboronate ester and 2,4,6-tri(4-pyridyl)-1,3,5-triazine. These cages can act as hosts for electron-rich planar aromatic systems such as triphenylene. Further, crystalline two-dimensional polymers were formed via dative B-N bonds between a triboronic ester and a ditopic pyridyl ligand. Use of an extended triboronate ester resulted in formation of a gel in toluene with a minimum gelation concentration of 0.5 wt%

Molecular Networks Based on Dative Boron-Nitrogen Bonds

The BN connection: Crystalline and soft molecular networks can be constructed using dative BN bonds (see picture). The networks are obtained in a one-step, three-component reaction involving a triboronic acid, a catechol, and a bipyridyl linker

Supramolecular polymers based on dative boron–nitrogen bonds

Heteroditopic monomers containing an arylboronate ester and a dialkyl-4-aminopyridine group aggregate via dative boron–nitrogen bonds to give main chain supramolecular polymers. The degree of polymerization can be tuned by changing the electronic and steric properties of the boronate ester