A metal-carbene template approach enables efficient synthesis of a functionalized cage-annulated crown ether

A facile synthetic method to form cage-annulated crown ether with anchored imidazolium units was developed. The present work verified the potential application of the metal-carbene template approach (MCTA) in the preparation of novel flexible polyimidazolium cages by photochemical [2+2] cycloaddition reactions and may provide a new method for the preparation of flexible pure organic cages with incorporation of a variety of functional sites.

[2+2] Photodimerization of Stilbazoles Promoted by Oxalic Acid in Suspension

In this study, a very simple technique to perform efficiently photodimerization of some vinylpyridines is reported. By irradiating a stirred mixture of several stilbazoles with solid oxalic acid dihydrate dispersed in a nonpolar (i.e., cyclohexane) or moderately polar (benzene, dichloromethane, dioxane) solvent, the corresponding dimeric cyclobutane adducts were obtained in high yields and excellent regio- and stereoselectivities. The strategy could also be applied successfully to oily, waxy, or even insoluble stilbazoles. Moreover, the oxalic acid loading could be lowered to substoichiometric amounts. When further optimizations were needed, our strategy was found to be highly flexible to identify other oligocarboxylic acids as alternative additives to improve, or even overturn, the regioselectivity. Oxalic acid and other oligocarboxylic acids were found to be capable of orienting more than 50 stilbazoles toward photodimerization under these conditions.

Photocycloaddition of S,S-Dioxo-benzothiophene-2-methanol, Reactivity in the Solid State and in Solution: Mechanistic Studies and Diastereoselective Formation of Cyclobutyl Rings

The formation of cyclobutane rings is a promising strategy in the development of potential drugs and/or synthetic intermediates, typically challenging to obtain due to their constrained nature. In this work, the [2 + 2] photocycloaddition reaction of S,S-dioxobenzothiophene-2-methanol was explored in microcrystalline powders and its outcome was compared to that observed in solution. It was found that the molecular constraints inherited within the crystal lattice provide an optimal environment that leads to photodimer 4 as the major product in ca. 9.6:0.4 diastereomeric ratios with conversions >95%. The photoreaction was analyzed via X-ray, displaying a crystalline-to-amorphous transformation and showing that units of monomer 2 align to generate the corresponding dimer with a syn-head-to-tail regio- and diastereoselectivity. This result contrasted with that obtained in solution, where the diastereomeric ratio varied as a function of the excited state that is generated, to yield mixtures of dimers 4 and 5 (anti-head-to-tail), or exclusively 5 in the triplet-sensitized photoreaction, in the presence of benzophenone. Density functional theory was used to elucidate a plausible detailed mechanism for the phototransformation, which aided in justifying the results that led to the corresponding dimers. X-ray crystallography allowed us to establish the stereochemical assignment of the obtained cyclobutyl rings. Thus, the use of solid-state or solution photochemistry can be used to gain control of diastereo- and regioselectivities in the formation of this important moiety.

Four new Zn(ii) and Cd(ii) coordination polymers using two amide-like aromatic multi-carboxylate ligands: synthesis, structures and lithium–selenium batteries application

Four new coordination polymers, {[Zn(3-PBI)(H₂O)]·2DMF}_n (1), [Cd(3-PBI)(DMF)]_n (2), {[Zn₄(μ₄-O)(4-PBI)₃]·3DMF}_n (3), {[Cd₄(4-PBI)₄(H₂O)₆]·13H₂O}_n (4), have been constructed from two isomeric flexible multi-carboxylate ligands, 3-H₂PBI = 5-(3-(pyridin-3-yl)benzamido)isophthalic acid and 4-H₂PBI = 5-(3-(pyridin-4-yl)benzamido)isophthalic acid. Structural analysis reveals that compound 1 is a one-dimensional (1D) ladder-like chain assembled by Zn(ii) ions and 3-PBI²⁻ ligands, which further extend into a 3D supramolecular structure through π⋯π stacking and interlayer (O–H⋯O) hydrogen bonding interactions. In compound 2, Cd²⁺ metal ions are connected by carboxylate groups to form [Cd₂(COO)₄] secondary building units (SBUs). The whole framework possesses a quadrilateral channel and constitutes a unique 3D (3,6)-connected rutile net with the Schläfli symbol of (4²·6¹⁰·8³)(4·6²)₂. As for 3, Zn(ii) ions are bridged by one μ₄-O and six carboxylate groups to form a tetranuclear [Zn₄(μ₄-O)(COO)₆] cluster, resulting in a rare (3,9)-connected 3D network. Compound 4 has an appealing 2D layered architecture involving two distinct topologies in the crystal structure, stacking in an unusual ABBABB mode (where A represents (4·8²) topology and B denotes kgd topology). Moreover, compound 2 is prepared as a support for active selenium through a melt-diffusion method. The obtained Cd-CP/Se electrode can be tested for lithium–selenium batteries and shows an initial capacity of 514 mA h g⁻¹ and a reversible capacity of 200 mA h g⁻¹ at 1C after 500 cycles. The good storage performance of Cd-CP/Se demonstrates it to be a prospective cathode material for lithium–selenium batteries.

Four new coordination polymers were constructed and compound 2 was used as a host to active selenium for Li–Se batteries.

Substituent effects of two isophthalate derivatives on the construction of cadmium coordination polymers incorporating a dipyridyl ligand

In recent years, the design and construction of crystalline coordination complexes by the assembly of metal ions with multitopic ligands have attracted considerable attention because of the unique architectures and potential applications of these compounds. Two new coordination polymers, namely poly[[μ-trans-1-(2-aminopyridin-3-yl)-2-(pyridin-4-yl)ethene-κ²N:N'](μ₃-5-methylisophthalato-κ⁴O¹,O^1':O³:O^3')cadmium(II)], [Cd(C₉H₆O₄)(C₁₂H₁₁N₃)]_n or [Cd(5-Me-ip)(2-NH₂-3,4-bpe)]_n, (I), and poly[[μ-trans-1-(2-aminopyridin-3-yl)-2-(pyridin-4-yl)ethene-κ²N:N'](μ₂-5-hydroxyisophthalato-κ⁴O¹,O^1':O³:O⁵)cadmium(II)], [Cd(C₈H₄O₅)(C₁₂H₁₁N₃)]_n or [Cd(5-HO-ip)(2-NH₂-3,4-bpe)]_n, (II), have been prepared hydrothermally by the self-assembly of Cd(NO₃)₂·4H₂O and trans-1-(2-aminopyridin-3-yl)-2-(pyridin-4-yl)ethene (2-NH₂-3,4-bpe) with two similar dicarboxylic acids, i.e. 5-methylisophthalic acid (5-Me-H₂ip) and 5-hydroxyisophthalic acid (5-HO-H₂ip). The coordination network of (I) is a two-dimensional sql net parallel to (101). Adjacent sql nets are further linked to form a three-dimensional supramolecular framework via hydrogen-bonding interactions. Compound (II) is a two-dimensional (3,5)-connected coordination network parallel to (010) with the point symbol (6³)(5⁵6⁴7). As the other reactants and reaction conditions are the same, the structural differences between (I) and (II) are undoubtedly determined by the different substituent groups in the 5-position of isophthalic acid. Both (I) and (II) exhibit good thermal stabilities and photoluminescence properties.

Varying the regiochemistry of a [2 + 2] cycloaddition reaction within isostructural hydrogen bonded cocrystals containing 4-stilbazole

Cocrystallization of 4-stilbazole with 4,6-diX resorcinol (X = Cl or Br) yields a pair of similar photoreactive solids that leads to different photoproducts.

Construction and photocatalytic properties of two metal-mediated coordination polymers based on benzene-1,3,5-tricarboxylic acid and trans-1-(pyridin-3-yl)-2-(pyridin-4-yl)ethene

With the rapid development of modern industry, water pollution has become an intractable environmental issue facing humans worldwide. In particular, the organic dyes discharged into natural water from dyestuffs, dyeing and the textile industry are the main sources of pollution in wastewater. To eliminate these types of pollutants, degradation of organic contaminants through a photocatalytic technique is an effective methodology. To exploit more crystalline photocatalysts for the degradation of organic dyes, two coordination polymers, namely catena-poly[[(3,5-dicarboxybenzene-1-carboxylato-κO¹)silver(I)]-μ-trans-1-(pyridin-3-yl)-2-(pyridin-4-yl)ethene-κ²N:N'], [Ag(C₉H₅O₆)(C₁₂H₁₀N₂)]_n or [Ag(H₂BTC)(3,4'-bpe)]_n, (I), and poly[[(μ₃-5-carboxybenzene-1,3-dicarboxylato-κ⁴O¹,O^1':O³:O³)[μ-trans-1-(pyridin-3-yl)-2-(pyridin-4-yl)ethene-κ²N:N']cadmium(II)] monohydrate], {[Cd(C₉H₄O₆)(C₁₂H₁₀N₂)]·H₂O}_n or {[Cd(HBTC)(3,4'-bpe)]·H₂O}_n, (II), have been prepared by the hydrothermal reactions of benzene-1,3,5-tricarboxylic acid (H₃BTC) and trans-1-(pyridin-3-yl)-2-(pyridin-4-yl)ethene (3,4'-bpe) in the presence of AgNO₃ or Cd(NO₃)₂·4H₂O, respectively. These two title compounds have been structurally characterized by IR spectroscopy, elemental analysis, single-crystal X-ray diffraction and powder X-ray diffraction. In (I), the Ag^I ions and organic ligands form a one-dimensional coordination chain, and adjacent coordination chains are connected by Ag...O interactions to give rise to a two-dimensional supramolecular network. Each two-dimensional network is entangled with other equivalent networks to generate an infrequent interlocked 2D→3D (2D and 3D are two- and three-dimensional, respectively) supramolecular framework. In (II), the Cd^II ions are bridged by the HBTC^2- and 3,4'-bpe ligands, which lie across centres of inversion, to give a two-dimensional coordination network. The thermal stabilities and photocatalytic properties of the title compounds have also been studied.