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.

Covalent connections between metal-organic frameworks and polymers including covalent organic frameworks

Hybrid composite materials combining metal-organic frameworks (MOFs) and polymers have emerged as a versatile platform for a broad range of applications. The crystalline, porous nature of MOFs and the flexibility and processability of polymers are synergistically integrated in MOF-polymer composite materials. Covalent bonds, which form between two distinct materials, have been extensively studied as a means of creating strong molecular connections to facilitate the dispersion of "hard" MOF particles in "soft" polymers. Numerous organic transformations have been applied to post-synthetically connect MOFs with polymeric species, resulting in a variety of covalently connected MOF-polymer systems with unique properties that are dependent on the characteristics of the MOFs, polymers, and connection modes. In this review, we provide a comprehensive overview of the development and strategies involved in preparing covalently connected MOFs and polymers, including recently developed MOF-covalent organic framework composites. The covalent bonds, grafting strategies, types of MOFs, and polymer backbones are summarized and categorized, along with their respective applications. We highlight how this knowledge can serve as a basis for preparing macromolecular composites with advanced functionality.

Photoreactive Crystals Exhibiting [2 + 2] Photocycloaddition Reaction and Dynamic Effects

ConspectusConducting a reaction in the solid state eliminates the usage of solvents. If such reactions are conducted in a single-crystal to single-crystal (SCSC) fashion, then structural characterization by single-crystal X-ray crystallography (SCXRD) techniques provides unequivocal structural details. Although topochemical principles govern, getting single crystals at the end of a SCSC reaction purely depends on the experimental skills of the researchers. SCSC reactions are common among solid-state [2 + 2] cycloaddition reactions (hereafter "photoreaction") after the classical work of Schmidt and co-workers in 1960s. Synthons and tectons in the crystal engineering box can be exploited to bring the functional groups into the required alignment and packing to achieve the desired chemical reactivities and physical properties, respectively. Bringing a pair of alkenes closer together in the organic molecules provides an effective starting point to achieve the goal of crystal engineering.Further, understanding and controlling photoreactivity in the solid state provide a gateway to designing new advanced materials, for example, making cycloreversible optical storage materials, photosalient and photomechanical materials, highly crystalline or even single-crystalline organic polymers, covalent organic framework structures, and organic polymers incorporated inside metal-organic frameworks (MOFs). Photoreactions often proceed in a SCSC manner due to the limited movements of the closely disposed reactive functional groups in the crystals. Thus, these photoreactions yield not only quantitative photoproducts but also regio- and stereospecificity, which are otherwise inaccessible by solution syntheses.The traditional definition of crystals being hard, rigid, and brittle is no longer valid ever since the mechanically responsive crystals were discovered. These dynamic crystals undergo various movements like curling, jumping, hopping, popping, splitting, and wiggling, when exposed to light (called "photosalient effect") or heat (called "thermosalient" effect). These crystals generate new methods of transforming light and heat energy into mechanical work. Recently, photosalient behavior during the [2 + 2] cycloaddition reaction under UV light has been frequently observed. With the emergence of the field of "crystal adaptronics", dynamic photoreactive crystals have emerged as smart actuating materials.This Account aims to provide an overview of the development in this area, since it has garnered much attention among solid state chemists. While presenting selected examples of important strategies, we try to illustrate the intentions and concepts behind the methods developed, which will help in a rational approach for the fabrication of advanced solid state materials. Apart from topochemical transformations, the important roles played by weak interactions, guest solvents, and mechanical grinding have been highlighted in several classes of compounds to show structural transformations that defy the expected outcomes. Overall, the progress of [2 + 2] cycloaddition reaction in solid state materials has been discussed from UV induced structural transformations to the development of smart actuating materials.

Fluorine as a robust balancer for tuning the reactivity of topo-photoreactions of chalcones and the photomechanical effects of molecular crystals

The higher the number of fluorine atoms, the higher the topological photo-induced [2 + 2] cycloaddition reactivity of chalcones.

Disappeared supramolecular isomer reappears with perylene guest

Among different types of polymorphism, disappearing polymorphism deals with the metastable kinetic form which can not be reproduced after its first isolation. In the world of coordination polymers (CPs) and metal-organic frameworks (MOFs), despite the fact that many types of supramolecular isomerism exist, we are unaware of disappearing supramolecular isomerism akin to disappearing polymorphism. This work reports a MOF with dia topology that could not be reproduced, but subsequent synthesis yielded another supramolecular isomer, a double-pillared-layer MOF. When perylene was added in the same reaction, the disappeared dia MOF reappeared with perylene as a guest in the channels. Interestingly, the photoluminescence of the dia MOF with a perylene guest is dominated by the emission of the guest molecule. The influence of guest molecules on the stabilization of the supramolecular isomers of a MOF opens up a strategy to access MOFs with different structures.

Formation of a four-bladed waterwheel-type chloro-bridged dicopper(ii) complex with dithiamacrocycle via double exo-coordination

A four-bladed waterwheel-like chloro-bridged dicopper(ii) complex! The self-assembly of O₃S₂-macrocycle (L) with copper(ii) nitrate afforded a chloro-bridged tetra(macrocycle) dicopper(ii) complex.

Effect of stepwise protonation of an N-containing ligand on the formation of metal–organic salts and coordination complexes in the solid state

Controlled synthesis of a series of metal–organic salts and coordination complexes is tuned by the protonation of ligand, and their transformations are induced by the solid–gas and concentration of [H⁺].

Reversible photo/thermal solid-state transformation of a coordination polymer

A 2D coordination polymer, 1, was synthesized, characterized, and investigated with single-crystal-to-single-crystal photoreaction and thermal pyrolysis.

Solid-State Photoinitiated Cycloaddition Reaction of 4,4′-(Ethene-1,2-diyl)bis(pyridinium) Dinitrate: Charge-Density Perspective on Initial Stage of the Reaction

Solid-state photoinitiated [2 + 2] cycloaddition reaction 2(H2bpe)(NO3)2 → (H4tpcb)(NO3)4 (bpe = 1,2-bis(pyrid-4-yl)ethylene; tpcb = 1,2,3,4-tetrakis(pyrid-4-yl)cyclobutane) was carried out in a single-crystal-to-single-crystal manner. The reaction product was characterized by means of X-ray diffraction and 1H NMR spectroscopy. Only the rctt-isomer of tpcb was found as the reaction product. Intermolecular interactions in a single crystal of (H2bpe)(NO3)2 were studied within the QTAIM approach. Although sum energy of strong and weak hydrogen bonds dominates in total packing energy, contribution of π…π stacking interactions to the packing energy is also prominent. At solid (H2bpe)(NO3)2, stacking of photoreactive H2bpe2+ cations is realized via N…C, C…C and C–H…C bonding, although no four-membered cycles formed by these bond paths was found in molecular graph representation. Reduced density gradient (RDG) surfaces and molecular Voronoi surfaces clearly demonstrate accumulation of charge density between olefin groups prone to take part in photoinitiated cycloaddition reactions. Good correlation between description of hydrogen bonding in terms of QTAIM and Voronoi approaches was demonstrated. The Voronoi approach confirmed that during the photoreaction the system of hydrogen bonds remained almost unchanged.

Metal/Carboxylate-Induced Versatile Structures of Nine 0D → 3D Complexes with Different Fluorescent and Electrochemical Behaviors

To investigate the effect of the polycarboxylates and metal ions on the assembly and structures of complexes based on a thiophene-containing bis-pyridyl-bis-amide N,N'-bis(pyridine-3-yl)thiophene-2,5-dicarboxamide (3-bptpa) ligand, nine 0D → 3D complexes of [Ni₂(3-bptpa)₄(1,2-BDC)₂(H₂O)₂] (1), [Ni(3-bptpa)(IP)(H₂O)₂]·H₂O (2), [Ni(3-bptpa)(5-MIP)(H₂O)₂]·H₂O (3), [Ni(3-bptpa)(5-NIP)(H₂O)] (4), [Ni(3-bptpa)(5-AIP)]·2H₂O (5), [Ni₂(OH)(3-bptpa)(1,3,5-BTC)]·DMA·5H₂O (6), [Cu(3-bptpa)(5-MIP)]·3H₂O (7), [Cu(3-bptpa)(5-AIP)(H₂O)_0.25]·H₂O (8), and [Cu(3-bptpa)(1,3,5-HBTC)] (9) (1,2-H₂BDC = 1,2-benzenedicarboxylic acid, H₂IP = 1,3-benzenedicarboxylic acid, 5-H₂MIP = 5-methylisophthalic acid, 5-H₂NIP = 5-nitroisophthalic acid, 5-H₂AIP = 5-aminoisophthalic acid, DMA = N,N'-dimethylacetamide, and 1,3,5-H₃BTC = 1,3,5-benzenetricarboxylic acid) have been hydrothermally/solvothermally synthesized and structurally characterized by IR, thermogravimetric, powder X-ray diffraction, and single-crystal X-ray diffraction. Complex 1 is a zero-dimensional (0D) bimetallic complex. Complexes 2 and 3 feature two similar one-dimensional ladderlike structures. Complex 4 displays a two-dimensional (2D) 4-connected network based on single-metallic nodes. Complex 5 shows a 2D double-layer structure containing a pair of 6³ [Ni(5-AIP)] honeycomblike sheets. Complex 6 is a 3,5-connected three-dimensional (3D) framework derived from bimetallic nodes and 6³ [Ni₂(OH)(1,3,5-BTC)] honeycomblike sheets. Complex 7 displays a 2D 4-connected grid based on bimetallic nodes. Complex 8 features a 2D double-layer structure based on two 4-connected [Cu(3-bptpa)(5-AIP)] sheets and bridging coordinated water molecules. Complex 9 is a 2D structure extended by incomplete deprotonation of 1,3,5-HBTC and 3-bptpa linkers. The effect of the metal ions and polycarboxylates on the structures of the title complexes was discussed, and the fluorescent properties of 1-9 were investigated. The carbon paste electrodes bulk-modified by complexes 3, 5, and 6-9 show different electrocatalytic activities for the oxidation of ascorbic acid as well as the reduction of hydrogen peroxide, nitrites, and bromates.

Metal-Organic Frameworks in Polymer Science: Polymerization Catalysis, Polymerization Environment, and Hybrid Materials

The development of metal-organic frameworks (MOFs) has had a significant impact on various fields of chemistry and materials science. Naturally, polymer science also exploited this novel type of material for various purposes, which is due to the defined porosity, high surface area, and catalytic activity of MOFs. The present review covers various topics of MOF/polymer research beginning with MOF-based polymerization catalysis. Furthermore, polymerization inside MOF pores as well as polymerization of MOF ligands is described, which have a significant effect on polymer structures. Finally, MOF/polymer hybrid and composite materials are highlighted, encompassing a range of material classes, like bulk materials, membranes, and dispersed materials. In the course of the review, various applications of MOF/polymer combinations are discussed (e.g., adsorption, gas separation, drug delivery, catalysis, organic electronics, and stimuli-responsive materials). Finally, past research is concluded and an outlook toward future development is provided.

Controlled polymerizations using metal-organic frameworks

This short review focuses on recent developments in polymerization reactions using metal-organic frameworks (MOFs). MOFs are crystalline porous materials that are able to tune their frameworks, enabling their use as promising media for polymerization. The precise design of the MOF structure is key to controlling polymerizations, allowing for the regulation of not only primary but also higher-order structures.

Functionalization of Metal-Organic Frameworks for Photoactive Materials

Metal-organic frameworks (MOFs) are intriguing platforms with multiple functionalities. Additional functionalization of MOFs generates novel materials for various applications. Here, three main topics are examined regarding the functionalization of MOFs for use as photoactive materials. The first is chemical approaches for postsynthetic modification of the metal clusters and organic linkers in MOFs; that is, sites on pore surfaces and chemical trapping of photoactive moieties within the pores, which create materials with chemical functionalities for water splitting and CO₂ reduction by light. The second topic focuses on the functionalization of MOFs for photochemical response and the versatile applications of such materials. State-of-the-art research on functionalizing MOFs through photochemical reactions on the pore surface and within the pores as guests is also summarized. The third topic introduces the functionalization of MOFs for photofunctional materials, including photoluminescent tuning and integration, photoluminescent LED devices and barcodes, and photophysical applications for chemical sensing. Finally, conclusions and perspectives on the fields are given.

2D and 3D lanthanide metal–organic frameworks constructed from three benzenedicarboxylate ligands: synthesis, structure and luminescent properties

Nineteen Ln-MOFs with four different crystal structures were prepared and the luminescence was studied.

Liquid-free single-crystal to single-crystal transformations in coordination polymers

Single-crystal to single-crystal (SCSC) transformations not only can create new materials, but also provide an opportunity to explore the process of forming a chemical bond. SCSC transformations discussed in this paper are confined to transformationsviaan absolutely liquid-free mode and involve the breakage and formation of new chemical bonds.

Single-crystal-to-single-crystal transformation of a coordination polymer from 2D to 3D by [2 + 2] photodimerization assisted by a coexisting flexible ligand

A 2D interdigitated [Ni₂(adipate)₂(spy)₄(H₂O)₂] was transformed to a 3D coordination polymer through [2 + 2] photodimerization with conformational changes of adipate ligands.

Interpenetrated Double Pillared-Layer CoII MOFs with pcu Topology

Three double pillared-layer CoII metal–organic frameworks (MOFs) with a pcu topology of a long, conformationally flexible, dipyridyl spacer ligand, 1,4-bis[2-(4-pyridyl)ethenyl]benzene (bpeb), and aromatic dicarboxylates (1,4-benzenedicarboxylate (bdc), 2,6-naphthalenedicarboxylate (ndc), and biphenyl-4,4′-dicarboxylate (bpdc)) have been synthesised and structurally characterised by X-ray crystallography. The MOFs are denoted as [Co2(bpeb)2(bdc)2]·DMF·3H2O (1), [Co2(bpeb)2(ndc)2]·1.75DMF·3.75H2O (2), and [Co2(bpeb)2(bpdc)2]·3.5DMF·4H2O (3). In the dinuclear repeating unit, four carboxylates are bonded to two CoII atoms forming a (4,4) layer structure. The axial positions are occupied by bpeb ligands. Of these, 1 and 2 have 2-fold interpenetration, whereas 3 displays 3-fold interpenetration. The two bpeb space ligands in 1 have trans,trans,trans and trans,cis,trans conformations. In contrast, the bpeb ligands in 2 and 3 have a trans,cis,trans conformation. Although the olefin groups in two adjacent bpeb ligands, as the double pillars in 2 and 3, satisfy the conditions for photo-dimerisation to occur, they are photo-inactive. The conformational changes of bpeb, bonding modes of the dicarboxylates, and pore sizes in these double pillared-layer compounds have been discussed.

Water-Resistant and Transparent Plastic Films from Functionalizable Organic Polymers: Coordination Polymers as Templates for Solid-State [2+2]-Photopolymerization

An organic polymer containing cyclobutanes and amides as backbones and pyridyl groups as sidearms was synthesized by single-crystal-to-single-crystal (SCSC) [2+2]-photopolymerization in the coordination polymers (CPs) of diene. The diene molecule was photo-inactive in its crystals and formed a triply intertwined 1D-helical CP with Cd(NO₃ )₂ and Cu(NO₃ )₂ salts. The 1D-CP was transformed into a coordination polymer of organic polymers containing threefold interpenetrated 3D-networks of CdSO₄ topology through a [2+2]-reaction in SCSC manner upon irradiation. The organic polymer was separated from its CPs and found to have an unusually high degree of polymerization for this type of reaction. Furthermore, the organic polymer was amenable for N-alkylation reactions such as methylation, propylation, and decylation. The formate salts of the organic polymer and the methylated polymer were shown to form plastic films with a combination of properties such as high transparency, tensile strengths, gas permeability, thermal stability, water-resistance, and resistance to other organic solvents. The methylated polymer was also able to capture chromate ions and anionic dyes from aqueous solutions.

Solid-state polymerisation via [2+2] cycloaddition reaction involving coordination polymers

Recent advancements in the construction of cyclobutane polymersviaphoto-dimerisation reaction in the monocrystalline solids of metal complexes, coordination polymers and metal–organic framework structures are reviewed.

Metal-Organic Frameworks via Emissive Metal-Carboxylate Zwitterion Intermediates

Pyridinemethanol-carboxylate esters form octahedral complexes with Zn(NO₃ )₂ in aqueous DMF that subsequently undergo hydrolysis at elevated temperatures to form metal-carboxylate zwitterions. In situ deprotonation of the hydroxy group leads to thermally robust, neutral MOFs. This stepwise synthesis can be controlled by temperature and is made possible by the subtle difference in reactivity of the functional groups.

Coordination assemblies of Zn(NO3)2 with 4-pyr-poly-2-ene and polycarboxylates: structural diversification and photoluminescence properties

Reactions of Zn(NO₃)₂·6H₂O with 4-pyr-poly-2-ene and five polycarboxylates afforded a series of coordination polymers with different architectures. Their thermal and photoluminescence properties were also investigated.

Dynamic structural transformations of coordination supramolecular systems upon exogenous stimulation

This feature article comments on the dynamic structural transformations of coordination supramolecular systems, which can be triggered by exposure to various exogenous stimuli such as concentration, temperature, light and mechanical force, as well as their synergic effect.

A novel example of double reactivity by either photochemical [2+2] or thermal additions of an ionic organic supramolecular assembly

An example of double reactivity in the solid state was achieved from an ionic array directed by charge-assisted hydrogen bonds.