Stepwise Host–Guest [2 + 2] Photoreaction in a Hydrogen-Bonded One-Dimensional Coordination Polymer to a Two-Dimensional Layered Structure

Two hydrogen-bonded interdigitated one-dimensional (1D) coordination polymers (CPs) were synthesized from Cd­(II) nitrate and 1,4-benzenedicarboxylate (bdc) with two 4-styrylpyridine (4spy) derivatives. In the solid state structure of 1D CP containing 2′-fluorostyrylpyridine (2F-4spy), a guest 2F-4spy was sandwiched between the terminal 2F-4spy ligands and the CC bonds of all the 2F-4spy are well-aligned in <i>host–guest-host–host-guest–host</i>- sequence infinitely. From time-dependent photoreaction studies, it has been found that the [2 + 2] photocycloaddition occurs between <i>host–guest</i> molecules first followed by <i>host–host</i> pairs in a two-step process, which resulted in the quantitative conversion of CC bond pairs to cyclobutane rings. It is a rare quantitative photoreaction between the <i>host</i> and <i>guest</i> molecules. Further, solvothermal crystallization of the final photoproduct furnished an interesting three-dimensional CP with <b>bcg</b> topology. Interestingly, 2NO₂-4spy also furnished a similar hydrogen-bonded 1D CP with parallel orientation of olefin bonds. Although the olefin bonds satisfy the Schmidt’s criteria for photoreactivity, it was found to be photoinert under UV light. This has been attributed to the steric hindrance caused by NO₂ substituent or the electron withdrawing effect

Solid-State Reactivity of Supramolecular Isomers: A Study of the <i>s</i>‑Block Coordination Polymers

Four coordination polymers of <i>s</i>-block metal ions, namely, Na­(I), K­(I), and Ba­(II) with <i>rctt</i>-cyclobutanetetracarboxylate (<i>rctt</i>-cbtc) ligand were synthesized, and their solid-state structures were determined by X-ray crystallography. Of these, [Na₂(<i>rctt</i>-cbtc<b>-</b>H₂)­(H₂O)₄] (<b>1</b>) and (<b>2</b>) are supramolecular isomers with <b>mog</b> and <b>pcu</b> topologies. While the three-dimensional structure of [K₂(<i>rctt</i>-cbtc)­(H₂O)₂] (<b>3</b>) is constructed based on a (6,8) net, [Ba₂(<i>rctt</i>-cbtc)­(H₂O)₆] (<b>4</b>) has <b>fsh</b> topology with (4,6) connectivity. Compounds <b>1</b>–<b>3</b> have been found to undergo thermal isomerization, contrary to the expected thermal cleavage of the cyclobutane ring, in the temperature range 200–250 °C cleanly to the <i>rtct</i> isomer in 50–85% yield, but not <b>4</b>. Interestingly, recrystallization of the isomerized product of <b>1</b> yielded single crystals of [Na₃(<i>rtct</i>-cbtc-H)­(H₂O)₃]_<i>n</i> (<b>5</b>). Although the composition has changed in this process, the stereochemistry at the cyclobutane ring was confirmed in this three-dimensional coordination polymer with a new topology

Synthesis, Characterization, and Photocatalytic Properties of In₂S₃, ZnIn₂S₄, and CdIn₂S₄ Nanocrystals

A one-pot method has been employed to synthesize the nanocrystals of In₂S₃, ZnIn₂S₄, and CdIn₂S₄. The single-source precursor [In­(bipy)­(SC­{O}­Ph)₃] has been used for making In₂S₃ nanocrystals. On the other hand, [Zn­(SC­{O}­Ph)₂]·2H₂O or [Cd­(SC­{O}­Ph)₂]·2H₂O was reacted with [In­(bipy)­(SC­{O}­Ph)₃] and decomposed to make the corresponding ternary metal indium sulfides. The nanocrystals have been characterized by X-ray powder diffraction (XRPD), transmission (TEM) and scanning electron microscopies (SEM), selected area electron diffraction (SAED) patterns, and energy-dispersive X-ray analysis (EDX). Parameters such as temperature, molar ratio of precursor to surfactant, duration of reaction time, and surfactant type were varied to investigate their influence on the morphology and size of nanomaterial. It was found that In₂S₃ exhibits different morphologies under different reaction conditions whereas the effect of these reactions conditions on the morphological evolution is not very prominent for ZnIn₂S₄ and CdIn₂S₄. All the synthesized metal ternary In₂S₃ showed efficient photocatalytic degradation of dye under ultraviolet (UV) light irradiation. We observed that the degradation of dye is much faster in chloroform than in the aqueous solution as the dispersion of nanoparticles is more homogeneous in chloroform solution. A comparison of the photocatalytic activity of In₂S₃ with ZnIn₂S₄ and CdIn₂S₄ having similar morphology and size shows that the photocatalytic activity of the ternary chalcogenides of In₂S₃ is considerably enhanced

Photoreactivity of Ag(I) Complexes and Coordination Polymers of Pyridyl Acrylic Acids

An attempt has been made to orient the CC bonds in <i>trans</i>-3-(3′-pyridyl)acrylic acid (3-PAH) and <i>trans</i>-3-(4′-pyridyl)acrylic acid (4-PAH) in the hydrogen-bonded coordination complexes and coordination polymers of Ag(I), utilizing the argentophilic interaction. Both neutral and deprotonated ligands were employed to synthesize the following compounds: [Ag(3-PAH)₂](BF₄) (<b>1</b>), [Ag(3-PAH)₂](ClO₄) (<b>2</b>), [Ag(4-PAH)₂](ClO₄)·H₂O (<b>3</b>), [Ag(3-PA)]·1.5H₂O (<b>4</b>), and [Ag(4-PA)] (<b>5</b>). Of these, <b>1–2</b> are isotypical hydrogen-bonded polymers of Ag(I) complexes and <b>3</b> is a hydrogen-bonded dimer, whereas <b>4</b> and <b>5</b> are coordination polymers. Compounds <b>1–4</b> undergo photodimerization in <i>head-to-head</i> fashion in the solid state. The photoreactivity of these compounds in solution was also investigated. The <i>head-to-head</i> photodimerized product of 4-PAH, namely, 3,4-bis(4′-pyridyl)cyclobutane-1,2-dicarboxylic acid (HH-4,4-BPCD), has been shown to be a potential ligand for synthesizing coordination polymers, by the isolation of [Ag₂(HH-4,4-BPCD)(H₂O)]·(2H₂O)(¹/₂MeOH), which has a two-dimensional polymeric structure in the solid state

Photoreactivity of Ag(I) Complexes and Coordination Polymers of Pyridyl Acrylic Acids

An attempt has been made to orient the CC bonds in <i>trans</i>-3-(3′-pyridyl)acrylic acid (3-PAH) and <i>trans</i>-3-(4′-pyridyl)acrylic acid (4-PAH) in the hydrogen-bonded coordination complexes and coordination polymers of Ag(I), utilizing the argentophilic interaction. Both neutral and deprotonated ligands were employed to synthesize the following compounds: [Ag(3-PAH)₂](BF₄) (<b>1</b>), [Ag(3-PAH)₂](ClO₄) (<b>2</b>), [Ag(4-PAH)₂](ClO₄)·H₂O (<b>3</b>), [Ag(3-PA)]·1.5H₂O (<b>4</b>), and [Ag(4-PA)] (<b>5</b>). Of these, <b>1–2</b> are isotypical hydrogen-bonded polymers of Ag(I) complexes and <b>3</b> is a hydrogen-bonded dimer, whereas <b>4</b> and <b>5</b> are coordination polymers. Compounds <b>1–4</b> undergo photodimerization in <i>head-to-head</i> fashion in the solid state. The photoreactivity of these compounds in solution was also investigated. The <i>head-to-head</i> photodimerized product of 4-PAH, namely, 3,4-bis(4′-pyridyl)cyclobutane-1,2-dicarboxylic acid (HH-4,4-BPCD), has been shown to be a potential ligand for synthesizing coordination polymers, by the isolation of [Ag₂(HH-4,4-BPCD)(H₂O)]·(2H₂O)(¹/₂MeOH), which has a two-dimensional polymeric structure in the solid state

An Unusual Interweaving in a 3-Fold Interpenetrated Pillared-Layer Zn(II) Coordination Polymer with a Long Spacer Ligand

This communication describes a unique interweaving of a pyridyl-based long linear spacer ligand, 1,4-bis­[2-(4-pyridyl)­ethenyl]­benzene (bpeb), in the triply interpenetrated pillar-layer porous coordination polymer [Zn₂(ndc)₂(bpeb)]·DMF·3H₂O (where ndc = 2,6-naphthalenedicarboxylate) containing a paddle-wheel secondary building unit (SBU) with α-Po topology. When the dicarboxylate is changed diethylpyrocarbonate (DEPC) from ndc to biphenyl-4,4′-dicarboxylate (bpdc), the reaction furnished a completely different 3-fold interpenetrating three-dimensional coordination polymer [Zn₃(bpdc)₃(bpeb)]·0.5DMSO·1.5H₂O having a uninodal eight connected network structure with hexagonal bipyramidal SBUs

Solid State Packing and Photoreactivity of Alkali Metal Salts of <i>trans</i>,<i>trans</i>-Muconate

Three alkali-metal salts of <i>trans</i>,<i>trans</i>-muconate (<i>muco</i>) <i>viz</i>. Li₂<i>muco</i> (<b>1</b>), Na₂<i>muco</i> (<b>2</b>), and K₂<i>muco</i> (<b>3</b>) have been prepared, and the influence of the crystal packing on the solid state photoreactivity has been investigated. Although the CC bonds of the <i>muco</i> ligands are oriented infinitely parallel in <b>1</b>, it was found to be photoinert. In contrast, the <i>muco</i> ligands of <b>2</b> and <b>3</b> in the crystalline state undergo photodimerization yielding cycloocta-3,7-diene-1,2,5,6-tetracarboxylate which has been formed stepwise via the [2 + 2] cycloaddition reaction of a single pair of CC bonds and subsequent Cope rearrangement. This study demonstrates how the size of the metal ion can influence the crystal packing in metal organic salts

Making Photoreactive <i>trans</i>-3‑(<i>n</i>′‑Pyridyl)acrylic Acid (<i>n</i> = 2, 3) with Head-to-Tail Orientation in the Solid State by Salt Formation

This work demonstrates that the photoinert <i>trans</i>-3-(2′-pyridyl)­acrylic acid (2-PA) can be made photoreactive by salt formation with HCl, CF₃CO₂H, and H₂SO₄. All three salts undergo photodimerization in head-to-tail (HT) fashion resulting in the formation of the corresponding dimer, 2,4-bis­(2′-pyridyl)-cyclobutane-1,3-dicarboxylic acid (HT-<i>rctt</i>-2,2′-BPCD), of which the former two salts, namely, [2-PAH]­Cl·H₂O and [(2-PAH)]­(CF₃CO₂) undergo single-crystal-to-single-crystal (SCSC) conversion. <i>trans</i>-3-(3′-Pyridyl)­acrylic acid (3-PA), on the other hand, is known to be photoreactive and undergoes photodimerization in head-to-head (HH) fashion producing the dimer HH-<i>rctt</i>-3,3′-BPCD. The HH-orientation of 3-PA can be flipped to HT by forming the ClO₄^– salt, which upon photodimerization produces HT-<i>rctt</i>-3,3′-BPCD. While HT-<i>rctt</i>-2,2′-BPCD exhibits isomerization in the presence of acid in solution, both the HH- and HT-<i>rctt</i>-3,3′-BPCD were inert under similar conditions. Our work demonstrates how the noncovalent intermolecular interactions can play a crucial role in the stereoselective synthesis and also emphasizes that the position of the nitrogen atom in the pyridyl ring is vital for the isomerization to occur in solution

Influence of Fluorine Substitution on the Unusual Solid-State [2 + 2] Photo-Cycloaddition Reaction between an Olefin and an Aromatic Ring

Solid-state [2 + 2] photo-cycloaddition reactions observed so far were exclusively between a pair of olefin bonds. Usually when the phenyl–olefin bonds have been closely aligned, they were found to be either photoinert or sliding of molecules takes place for [2 + 2] cycloaddition reaction between olefins in the solid state, although intramolecular phenyl–olefin reactions are well-known in solution. In the crystal structure of [Zn₂(ptol)₄­(4spy)₂] (ptol = <i>para</i>-toluate), the neighboring 4-styrylpyridine (4spy) ligands are organized in a head-to-tail manner. On one side of the complex in the crystal structure, the olefin bonds in the 4spy pairs are perfectly aligned to undergo cycloaddition reaction, but on the other side, the olefin bond pairs are slightly offset and found to be photoinert at 223 K forming only a dimer in single crystals. The sliding of 4spy groups has been restricted by the steric hindrance of the adjacent methyl group of the ptol ligands. A similar packing of 2-fluoro-4′-styrylpyridine (2F-4spy) pairs was found in [Zn₂(ptol)₄­(2F-4spy)₂]. Again, normal cycloaddition reaction occurs on one side of the 2F-4spy ligand pairs, whereas the second offset 2F-4spy ligand pairs undergo a rare [2 + 2] cycloaddition reaction between the fluorophenyl group and olefin bond resulting in the formation of a one-dimensional coordination polymers containing a bicyclic product in a quantitative yield. The bicyclic ring in the photoproduct can be thermally cleaved back to olefin and phenyl groups. These observations have been confirmed by single-crystal X-ray crystallography, ¹H NMR, and ¹⁹F NMR studies. Density functional theory calculations were performed to elucidate the nature of the interactions between the fluorophenyl and olefin groups. The greater reduction of aromaticity of 2F-4spy in the excited singlet state compared to the 4spy system may explain the observed reactivity difference between the two systems. The improved reactivity in 2F-4spy may also be attributed to the fact that the olefin–phenyl distance is shorter in 2F-4spy than in 4spy (3.63 versus 3.69 Å). This solid state phenyl–olefin photodimerization helps to pave the way for making new bicyclic derivatives

Photosalient Behavior of Photoreactive Crystals

Being documented with only about a dozen serendipitous observations, the photosalient effect, where crystals leap when exposed to light, is considered a very rare phenomenon. Here, with a set of structurally related materials that undergo [2 + 2] photocycloaddition we present evidence that this effect is more common than it has been realized in the past, and we seek to establish correlations with the kinematics and the crystal structure toward rational design of photosalient materials. To that end, nine photoreactive complexes AgL₂X₂ (L = 4-styrylpyridine, 2′-fluoro-4-styrylpyridine, and 3′-fluoro-4-styrylpyridine, X = BF₄^–, ClO₄^– and NO₃^–) were prepared. The [AgL₂]⁺ cations in these structures pack by both head-to-head and head-to-tail alignment of the styrylpyridine ligands. Crystals of six out of the nine complexes were photosalient and popped, hopped, and/or leaped when exposed to UV light. It is concluded that the occurrence of the photosalient effect is determined not only by the nature of the ligand but also by the crystal packing which directs the magnitude, direction, and rate of volume expansion during the photoreaction