Regulation of Crystal Structures and Solid-State Photoreactivity of Diolefin Coordination Polymers by Carboxylate Ligands

Abstract

Olefinic coordination polymers (CPs) have recently drawn more attention, owing to the many possibilities in conformational conversions and photochemical reactivity that olefin molecules offer. In the presence of different carboxylic acids, we utilize one diolefin ligand 4,4′-((1E,1′E)-(2,5-dimethoxyl-1,4-phenylene)bis(ethene-2,1-diyl))dipyridine (OCH3-bpeb) and Cd(II) to assemble six different crystalline CPs (1–6). By fine-tuning the substituent size, carboxyl group number, and geometrical configuration of carboxylate ligands, these diolefin CPs show quite different crystal architecture models, from one-dimensional intersecting stacking to one-dimensional parallel stacking to three-dimensional interpenetrated structure. Of these, four kinds of CPs (1, 2, 5, and 6) are demonstrated to be photoreactive for [2 + 2] cycloaddition reactions, as confirmed by proton nuclear magnetic resonance and single-crystal X-ray diffraction. Both 2 and 5 can be dimerized into different cyclobutane products in a single-crystal-to-single-crystal manner under visible light, and remarkably, the photocycloaddition reaction of 5 involves a rare phase transition with structural symmetry enhancement from P 1̅ to P2/n. This work demonstrates the power of carboxylate ligands in tuning single crystal structures and photocycloaddition reactions of CPs, which provides important references for the further exploration of other physicochemical properties of functionalized olefin-containing complexes.

Construction of olefinic coordination polymer single crystal platforms: precise organic synthesis, in situ exploration of reaction mechanisms and beyond

“…Derivatives of L 17 and L 18 , such as 1,4-bis(2-(3-pyridyl)ethenyl)benzene (L 20 ), 4,4 0 -((2,5-dimethyl-1,4-phenylene)bis(ethene-2,1diyl))dipyridine (L 21 ), 4,4 0 -((2,5-dioxymethyl-1,4-phenylene)bis (ethene-2,1-diyl))dipyridine (L 22 ) and 5-fluoro-1,3-bis(2-(4pyridyl)ethenyl)benzene (L 23 ), have been reported to yield CP single crystal platforms (104-114). [129][130][131][132][133][134] These diolefinic ligands contain different substituents or have their pyridine nitrogen atoms placed differently, providing access to versatile structural topologies and diverse [2+2] photocycloaddition reactions. Modification of the olefin ligands allows to some extent fine tuning of the alignment of olefin pairs, the orientation, and the distance between proximate CQC bonds, providing increased opportunities for the exploration of new physicochemical properties and potential applications.…”

“…(c) and (d) Emission spectra of 112-Vis in water after the addition of different concentrations of Cr 2 O 7 2À and CrO 4 2À. Reproduced with permission from ref 132. Copyright 2023, the American Chemical Society.…”

Solvent-Dependent Zn(II) Supramolecular Isomers and [2 + 2] Photocycloaddition Reaction via an SCSC Transformation

“…Taking inspiration from the building blocks of general MOFs, a combination of bipyridyl olefin ligands and carboxylate coligands with appropriate divalent metal ions have been successfully employed in constructing a range of photoreactive MOFs. , In general, mono- and dicarboxylates can act as chelating terminal ligands and dianionic spacers, respectively. , While dipyridyl olefins are somewhat multifunctional building blocks that can be used as photoreaction sites, linker, conjugated chromophore, and π–π stacking sites. We previously introduced a reversible photoinduced polymerization and thermal depolymerization of zinc(II) MOF with a herringbone-patterned slip-stacked packing of dipyridyl dienes via a single-crystal-to-single-crystal (SCSC) manner …”