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

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

Contrast Solid-State Photoreactive Behavior of Two Two-Dimensional Zn(II) Coordination Polymers

A two-dimensional photoreactive coordination polymer (2D CP), [Zn₂(Fumarate)₂(H₂O)₂(2F-spy)₄] (<b>1</b>) (2F-spy = 2′-fluoro-4-styrylpyridine), undergoes partial [2 + 2] cycloaddition reaction under UV light in a single-crystal-to-single-crystal manner to a three-dimensional (3D) CP [Zn₂(Fumarate)₂(H₂O)₂(2F-spy)₃(<i>rctt</i>-2F-ppcb)_0.5] (<b>2</b>) (where <i>rctt</i>-2F-ppcb = 1,3-bis­(4′-pyridyl)-2,4-bis­(2′-fluoro-phenyl)­cyclobutane), whereas another similar photoreactive 2D CP, [Zn₂(Fumarate)₂(3F-spy)₂] (<b>3</b>) (3F-spy = 3′-fluoro-4-styrylpyridine), when exposed to UV light, forms a cyclobutane ring arising from the hetero-cross-coupling of 3F-spy and fumarate, in addition to the expected cyclobutane ring, <i>rctt</i>-3F-ppcb (<i>rctt</i>-3F-ppcb = 1,3-bis­(4′-pyridyl)-2,4-bis­(3′-fluoro-phenyl)­cyclobutane) by the [2 + 2] cycloaddition reaction of 3F-spy pairs aligned in a head-to-tail (HT) fashion. It is unusual to observe two different photoproducts in a solid-state [2 + 2] photo-cycloaddition reaction involving CPs. It is possible because the metal ions appear to support the reactions between two different types of ligands

Putting the Squeeze on CH₄ and CO₂ through Control over Interpenetration in Diamondoid Nets

We report the synthesis, structure, and sorption properties of a family of eight diamondoid (<b>dia</b>) metal–organic materials (MOMs) that are sustained by Co­(II) or Zn­(II) cations linked by one of three rigid ligands: 4-(2-(4-pyridyl)­ethenyl)­benzoate (<b>1</b>), 4-(pyridin-4-yl)­benzoate (<b>2</b>), and 4-(pyridin-4-yl)­acrylate (<b>3</b>). Pore size control in this family of <b>dia</b> nets was exerted by two approaches: changing the length of the linker ligand from <b>1</b> to <b>3</b>, and using solvent as a template to control the level of interpenetration in nets based upon <b>1</b> and <b>3</b>. The resulting MOMs, dia-8i-<b>1</b>, dia-5i-<b>3</b>, dia-7i-<b>1</b>-Zn, dia-7i-<b>1</b>-Co, dia-4i-<b>3</b>-a, dia-4i-<b>3</b>-b, dia-4i-<b>2</b>, and dia-4i-<b>1</b>, exhibit 1D channels with pore limiting diameters (PLDs) of 1.64, 2.90, 5.06, 5.28, 8.57, 8.83, 11.86, and 18.25 Å, respectively. We selected <b>dia</b> nets for this study for the following reasons: their 1D channels facilitate study of the impact of pore size on gas sorption parameters in situations where pore chemistry is similar (pyridyl benzoate-type linkers) or identical (in the case of polymorphs), and their saturated metal centers eliminate open metal sites from dominating sorbent–solvate interactions and possibly masking the effect of pore size. Our data reveal that smaller pore sizes offer stronger interactions, as determined by the isosteric heat of adsorption (<i>Q</i>_st) and the steepness of the adsorption isotherm in the low-pressure region. The porous MOM with the smallest PLD suitable for physisorption, dia-7i-<b>1</b>-Co, was thereby found to exhibit the highest <i>Q</i>_st values for CO₂ and CH₄. Indeed, dia-7i-<b>1</b>-Co exhibits a <i>Q</i>_st for CH₄ of 26.7 kJ/mol, which was validated through grand canonical Monte Carlo simulation studies of CH₄ adsorption. This <i>Q</i>_st value is considerably higher than those found in covalent organic frameworks and other MOMs with unsaturated metal centers. These results therefore further validate the critical role that PLD plays in gas adsorption by porous MOMs

Elusive Network Topology of a 5‑Connected Self-Catenated 3D Coordination Polymer: Featuring Ligand Formation via the In Situ S–S Bond

This article describes the synthesis of a new Zn(II)-based three-dimensional coordination polymer (3D CP) [Zn2(4,4′-dsb)2(4,4′-bpy)3]·(solvent)x [H24,4′-dsb = 4,4′-disulfanediyldibenzoic acid and 4,4′-bipyridine (4,4′-bpy)] (1). Here, the originally used 4-mercaptobenzoic acid (4-mba) undergoes in situ dimerization via the S–S bond to produce H24,4′-dsb. Fascinatingly, compound 1 exhibits a scarcely reported self-catenated 5-connected underlying net with point symbol {42·68}. As far as our knowledge is concerned, this tangled network is the first of this kind among CPs. The calculated highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) band gap computed from density functional theory (DFT) calculation along with well-corroborated experimental values obtained by Tauc’s plot reveals the conducting nature of the synthesized material

Influence of Interpenetration in Diamondoid Metal–Organic Frameworks on the Photoreactivity and Sensing Properties

The degree of interpenetration is known to influence the gas sorption, catalytic, magnetic and nonlinear optical properties, chirality, and sensing of various molecules but not the solid-state [2 + 2] photocycloaddition reaction. In our previous studies of a solvothermal reaction using dimethylacetamide (DMA) as one of the solvents, a photoreactive 6-fold interpenetrated metal–organic framework with <b>dia</b> topology, [Zn­(bpeb)­(bdc)] (<b>1</b>) [bpeb = 1,4-bis­[2-(4′-pyridyl)­ethenyl]­benzene; bdc = 1,4-benzenecarboxylate], was isolated. Because of the slip-stacked alignment of a dipyridyl ligand with two conjugated olefin bonds, the [2 + 2] cycloaddition reaction occurs under UV light leading to the formation of an organic polymer ligand fused with a coordination polymer, <b>2</b>. On the contrary, under similar conditions when diethylformamide was used instead of DMA, a 5-fold interpenetrated structure, <b>3</b>, with the same <b>dia</b> topology was obtained in this work. This has been found to be photostable as also predicted from the analysis of the solid state structure. All the solids show interesting photoluminescence properties, and the emissions were preferentially quenched by curcumin to make these materials as potentially useful sensing agents