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

Olefin [2+2] photocycloaddition reactions based on coordination-bond templates provide numerous advantages for the selective synthesis of cyclobutane compounds. This review outlines the recent advances in the design and construction of single crystal platforms of olefinic coordination polymers for precise organic synthesis, in situ exploration of reaction mechanisms, and possible developments as comprehensively as possible. Numerous examples are presented to illustrate how the arrangements of the olefin pairs influence the solid-state photoreactivity and examine the types of cyclobutane products. Furthermore, the photocycloaddition reaction mechanisms are investigated by combining advanced techniques such as single crystal X-ray diffraction, powder X-ray diffraction, nuclear magnetic resonance, infrared spectroscopy, fluorescence spectroscopy, laser scanning confocal microscopy and theoretical calculations. Finally, potential applications resulting from promising physicochemical properties before and after photoreactions are discussed, and existing challenges and possible solutions are also proposed.

The crystal structure of poly[diaqua-bis(μ 3-5-bromobenzene-1,3-dicarboxylato-κ 3 O,O,O′)-(μ 2-1,3-bis-(4-pyridyl)-propane-κ 2 N,N′)-dizinc(II))] – 5-bromobenzene-1,3-dicarboxylic acid [2/1], C37H29Br3N2O14Zn2

C37H29Br3N2O14Zn2, monoclinic, P21/m (no. 11), a = 8.2047(6) Å, b = 28.6129(13) Å, c = 8.8721(7) Å, β = 112.069(9)°, V = 1930.2(3) Å3, Z = 2, R gt(F) = 0.0588, wR ref(F 2) = 0.1547, T = 200 K.

An europium(III) metal-organic framework as a multi-responsive luminescent sensor for highly sensitive and selective detection of 4-nitrophenol and I- and Fe3+ ions in water

A luminescence sensor based on an europium(III)-based lanthanide-organic framework, [Eu(BCB)(DMF)]·(DMF)_1.5(H₂O)₂ (1), was synthesized via a solvothermal method using 4,4',4''-benzenetricarbonyltribenzoic acid (H₃BCB) as a bridging ligand. Single-crystal X-ray diffraction indicates that Eu centers are eight-coordinated with a trigonal dodecahedron and a square antiprismatic configuration, and adjacent Eu atoms are bridged by BCB organic linkers to form a 3D rod-packing structure. Photoluminescence studies show that compound 1 emits bright red luminescence and behaves as a multi-responsive luminescent sensor toward 4-nitrophenol (4-NP) and I^- and Fe³⁺ ions in water with high sensitivity, selectivity and low detection limits. Furthermore, the possible luminescence sensing mechanisms were also investigated by PXRD analysis, UV-vis spectroscopy and X-ray photoelectron spectroscopy (XPS). The recognition mechanism for 4-NP and I^- ions can be attributed to the competition absorption and that for Fe³⁺ ions is considered to be a multi-quenching mechanism dominated by competition absorption. This study demonstrates that the lanthanide-based MOF might be a promising candidate for the detection of 4-NP and I^- and Fe³⁺ ions in aqueous medium.

A zinc(II) coordination polymer based on a flexible bis(benzimidazole) ligand: synthesis, crystal structure and fluorescence study

A new one-dimensional Zn(II) coordination polymer, {[ZnCl2(BBM)]·CH3OH} n (2,2-(1,4-butanediyl)bis-1,3-benzimidazole [BBM]), has been obtained from the hydrothermal reaction of zinc chloride with the flexible bis-benzimidazole ligand BBM and characterized by single-crystal X-ray diffraction, elemental analysis, IR and UV–vis spectra. Structural analysis has revealed that the BBM ligand connects the Zn(II) atoms to form a square-wave chain, which is further extended into supramolecular layers through hydrogen bonds and π···π stacking interactions. Solid-state fluorescence investigations showed that the Zn(II) coordination polymer has an emission peak at 381 nm upon excitation at 330 nm, which is attributed to ligand-centered luminescence. It is only slightly red shifted as compared to the ligand but partially quenched due to the strong π···π stacking interactions.

Functional group induced structural diversities and photocatalytic, magnetic and luminescence sensing properties of four cobalt(ii) coordination polymers based on 1,3,5-tris(2-methylimidazol-1-yl)benzene

Based on the designed tripodal linker timb, four cobalt(ii) coordination polymers, {[Co₄(timb)₂(Br–IPA)₄]·5H₂O}_n (1), {[Co(timb)_0.5(NH₂–IPA)]·4H₂O}_n (2), {[Co₅(timb)₄(OH–IPA)₄]·2NO₃·2DMA·2H₂O}_n (3), and {[Co₃(timb)₂(SO₃–IPA)₂(H₂O)₂]·8H₂O}_n (4), have been obtained.

From lamellar net to bilayered-lamella and to porous pillared-bilayer: reversible crystal-to-crystal transformation, CO2 adsorption, and fluorescence detection of Fe3+, Al3+, Cr3+, MnO4−, and Cr2O72− in water

Layered coordination polymers of different network topologies have showed reversible structural transformations and fluorescence detection toward Fe³⁺, Al³⁺, Cr³⁺, MnO₄^–, and Cr₂O₇^2– in water.

[2 + 2] cycloaddition reaction and luminescent sensing of Fe3+ and Cr2O72− ions by a cadmium-based coordination polymer

A cadmium-based coordination polymer can produce the corresponding photoproduct via [2 + 2] cycloaddition reaction, and can detect both Fe³⁺ and Cr₂O₇²⁻ ions.