English

• 0   Introduction

  Polymer-metal coordination complexes (PMCCs) demonstrate as an emerging functional material in which polymer ligands attach to metal ions usually via coordination bonds. PMCCs are attracting increasing attention since the mid of 1990s because of the development of new synthesis strategies and their potential applications as functional materials for conductive ^[1], sensing ^[2], self-healing ^[3], luminescent ^[4-5], stimuli responsive ^[6], nanoscience ^[7], etc ^[8-9]. However, it is always a great challenge to prepare crystalline and porous PMCCs due to the high flexibility, random conformation of polymer ligands and lack of approp-riate synthesis methods. Coordination complexes including coordination polymers (CPs) and metal-organic frameworks (MOFs) consist of central metal ions or metal clusters connected by organic ligands via coordination bonds. Due to the regular coordination geometry of metal centers (e.g. Fe favors to form 6-coordinated octahedral geometry) and the reversibility of coordination bonds, coordination complexes can form highly crystalline materials with defined structures of various topologies (e.g. pcu, nbo, rho, sql) ^[10-13]. Coor-dination complexes are feasible to form large crystals which are suitable to single-crystal X-ray diffraction (SCXRD). Moreover, coordination complexes especially MOFs possess the word-record highest surface areas ^[14](Langmuir surface area around 10 000 m²·g^-1) among all known porous materials including zeolite, carbon, mesoporous silica and so on. Coordination complexes have attracted great attentions because they demon-strate plenty of promising applications such as gas storage and separation ^[15], drug delivery ^[16], conductivity ^[17] and so on. PMCCs possess the potential to harness not only the advantage of polymers such as facile fabrication of films, good processability and high chemical stability, but also the advantage of coordination complexes such as structure robustness, high crystallinity, well-determined structures and permanent porosity. In this review, we summarize the reported PMCCs which possess high crystallinity and porosity, and discuss how to design and synthesize this kind of functional PMCCs. Moreover, we will discuss how to characterize PMCCs and list the challenges and chances in this area.

  1   Photo-induced polymerization method

  The topochemical solid-sate reaction have attracted scientists′ great attention since this reaction is solvent-free, atom economic and environmental friendly. Ascribed to the mild reaction condition and gentle treatment, materials can possess their crystall-inity via a single-crystal to single-crystal transforma-tion manner under photo irradiation. Both single-crystal, powder X-ray diffraction spectra (PXRD) and Infrared Spectroscopy (IR) spectra can help to under-stand the structural changes in anatomic-level ^[18-19]. Therefore, photo-induced polymerization reaction is a feasible method to transform a crystalline coordination complex which contains photo reactive monomer into a crystalline PMCC. A wide variety of photo-active groups have been employed for photo-polymerization reactions such as olefins ^[20-21], anthracenes ^[22-24] and ace-tylenes ^[25-27] or their derivatives. For olefin groups, in order to undergo [2+2] photo-cycloaddition reaction, the C=C bonds should be aligned parallel and the distance should be lower than 0.42 nm proposed by Schmidt et al. ^[28]. For the anthracenes, the carbon atoms in 9, 10 positions of the anthracenes also follow the same rules to perform the [4+4] cycloaddition reactions ^[29]. However, the acetylenes obey a new rule to perform 1, 4-cycloaddition reaction. The distance of acetylene groups is approximately 0.35 nm, which represents the van der Waals contact between the adjacent molecules. And when the aligned angle is about 45° ^[30-31], acetylene groups can be polymerized via topochemical 1, 4-cycloaddition. In order to perform a photocycloaddition reaction, a lot of effort has been made to align the photo-active groups in a favorable stacking arrangement which is the key factor in photocycloaddition reactions with the help of self-assembly techniques such as hydrogen bonds, donor acceptor, coordination bonds and π-π stacking intera-ctions ^[32-34] etc. If the photo-active groups can be stacked head to tail, when the photo-active groups link together under light source, polymer-metal coordina-tion complexes will be obtained. This method will make it possible to synthesis large crystal of polymers. However, among these interactions, coordination bond is rarely studied and employed in the preparation of PMCCs.

  Vittal et al. reported to use 1, 4-bis[2-(4′-pyridyl)ethenyl]benzene(bpeb) as a photo-active ligand to form a non-porous MOF, [Zn₂(bpeb)-(bdc)(fa)₂] ^[35]. This MOF can undergo [2+2] cycloaddition reaction in a single-crystal to single-crystal manner to generate a non-interpenetrated 3D structure in which bpeb ligands polymerized to form 1D chain polymers (Fig. 1). The solid-state photoluminescence spectra are also recorded to tract the reaction process. The MOF before irradia-tion shows a strong green emission, while the MOF after irradiation has a weaker emission which is blue shifted to stronger blue emission. This new PMCC compound is unlikely prepared by a direct synthesis strategy from polymer ligands.

  图1 SCSC transformation from a MOF to a PMCC under UV light by polymerization and the diagram of the polymer (a), photographs of crystals under room light and UV-365 nm light (b) ^[35] Figure1. SCSC transformation from a MOF to a PMCC under UV light by polymerization and the diagram of the polymer (a), photographs of crystals under room light and UV-365 nm light (b) ^[35]

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  Vittal et al. ^[36] reported the crystal structure of a 3D Zn-based PMCC fused with an 1D organic polymer ligand which is made in situ by a [2+2] cycloaddition reaction of a six-fold interpenetrated 3D MOFs. The crystallinity of starting 3D MOF after irradiation under 365 nm UV lamp is retained and the structure of the 1D organic polymer is determined by single-crystal X-ray diffraction. This organic polymer ligand can be depolymerized in a SCSC fashion by heating at 250 ℃ for 3 h, the powder X-ray diffraction (PXRD) date (Fig. 2b) shows that the structure reverts back to the original MOF structure. Gas sorption study reveals that this PMCC can adsorb a small amount of CO₂ at 195 K and 100 kPa.

  图2 Reversible polymerization by [2+2] photo-cycloaddition under UV lamp and depolymerization on heating (a), PXRD patterns for as synthesized, after UV-irradiation and after heating (b) ^[36] Figure2. Reversible polymerization by [2+2] photo-cycloaddition under UV lamp and depolymerization on heating (a), PXRD patterns for as synthesized, after UV-irradiation and after heating (b) ^[36]

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  2   Coordination induced self-assembly method

  According to the knowledge of traditional coordination chemistry, organic chain polymer cannot directly react with metals to form crystalline PMCCs because organic chain polymers are mostly amor-phous, flexible and non-porous. Moreover, almost all coordination complexes are prepared from small organic ligands. Therefore, it is always a great challenge to directly prepare PMCCs from organic polymers. Until recently, Cohen et al., for the first time, demonstrate that amorphous, linear, and nonporous polymer ligands are possible to coordinate with metal ions to construct highly crystalline coordination polymers (polyMOFs) via coordination bond induced self-assembly processes. This method makes use of the polymer ligands to react with metal ions directly to synthesize PMCCs which possess not only high crystalline and high porosity inheriting from MOFs, but also the chemical stability, flexibility, easy film formation and good proccessability from the organic polymer.

  In 2015, Zhang et al. ^[37] reported a straightforward strategy to prepare highly crystalline MCPs from poly-ether ligands (pbdc-xa) which contain repeated 1, 4-benzenedicarboxylic acid (H₂bdc) unites. A series of polycrystalline hybrid materials with IRMOF networks were prepared upon hydrothermal reactions of pbdc-xa ligands with Zn^Ⅱ cations. PXRD and scanning electron microscope (SEM) confirm these materials exhibit the same structures as IRMOF-1. Gas-sorption studies confirm these materials are highly porous. As shown in Fig. 3, Zn-pbdc-7a and Zn-pbdc-8a all exhibit typical type Ⅰ isotherms, indicating a uniform microporous structure (Fig. 3b) compared to pbdc-xa polymers. Moreover, these materials can sorb more CO₂ than the parent MOF-5.

  图3 IRMOF derivatives construct from an H₂bdc ligand derivative, a cross-linked H₂bdc ligand, and a polymeric H₂bdc polymer ligand with Zn²⁺ (a), N₂ sorption isotherms for polyMOFs (top) and CO₂ adsorption isotherms at 298 K (bottom) (b) ^[37] Figure3. IRMOF derivatives construct from an H₂bdc ligand derivative, a cross-linked H₂bdc ligand, and a polymeric H₂bdc polymer ligand with Zn²⁺ (a), N₂ sorption isotherms for polyMOFs (top) and CO₂ adsorption isotherms at 298 K (bottom) (b) ^[37]

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  Zhang et al. also demonstrate that this synthesis strategy can not only access the IRMOF structure, but also generates more MOF structures via a mixed ligands strategy (Fig. 4) ^[38]. Reaction of pbdc-xa and bridging linkers including dabco(1, 4-diazabicyclo octane), bpy(4, 4′-bipyridine) with Zn²⁺ or Cu²⁺ cations afford a series of new PMCCs. Gas sorption studies reveal that these materials exhibit relatively high CO₂ sorption but low N₂ sorption, making them promising materials for CO₂/N₂ separations. Furthermore, these new PMCCs exhibit much higher water stability compared to their parent MOFs without polymers inside. It can be ascribed to the hydrophobicity of polymers ligands.

  图4 Design concept for creating a polyMOF analogue of MOF via replacing dangling groups by polymer chains (a), N₂ sorption and CO₂ sorption isotherms for polyMOFs (b) ^[38] Figure4. Design concept for creating a polyMOF analogue of MOF via replacing dangling groups by polymer chains (a), N₂ sorption and CO₂ sorption isotherms for polyMOFs (b) ^[38]

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  Very recently, Cohen et al. reported the first PMCCs with a UiO-66 architecture, prepared from polymer with various alkyl spacers, molecular weights, and dispersities ^[39]. Indeed, PXRD confirm that polyUiO -66 form only with polymers of a certain linker spacing (pbdc-xa, x=3~8). The morphology and particle size of polyUiO-66 are investigated using SEM. The pbdc-6a-u is obtained composed of very small, crystalline nanostructures (Fig. 5a). Pbdc-8a-u exhibit thin and brittle crystalline films (Fig. 5b). The pbdc-10a does not form crystalline polyUiO-66 and only amorphous material is produced. The sorption behavior of polyUiO-66 is provided by nitrogen gas adsorption. From Fig. 5c and Fig. 5d, the surface area of polyUiO-66 materials were about 200~400 m²·g^-1, which were lower than the parent UiO-66 (1 000~1 500 m²·g^-1). This result is ascribed to the pore filling of methylene in the polymer ligands, however, indicate the polyMOF is micro- and meso-porous material.

  图5 PXRD patterns, SEM images and N₂ sorption isotherms of polyMOF prepared from different polymer ligands (a~d) ^[39] Figure5. PXRD patterns, SEM images and N₂ sorption isotherms of polyMOF prepared from different polymer ligands (a~d) ^[39]

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  Johnson et al. ^[40] synthesized a series of uniform oligomeric polyMOF ligands with alkyne end groups via an iterative exponential growth (IEG) strategy. When these ligands are coupled with Zn ions, a novel “block co-polyMOF” (BCPMOF) is yielded. Revealed by PXRD, BCPMOFs possessed the MOF-5 (IRMOF-1) structure same as polyMOFs reported by Cohen et al. and represent a higher stability than the parent MOF-5 and polyMOF. SEM and transmission electron microscope (TEM) (Fig. 6) images reveal BCPMOFs can form a thin polymer film.

  图6 SEM images of L_4-Zn (a), L₄PS-Zn dried at RT (b) and TEM image of L₄PS-Zn dried at RT (c), Schematic of L₄PS-Zn depicting a crystalline polyMOF domain embedded within a PS matrix (d) ^[40] Figure6. SEM images of L_4-Zn (a), L₄PS-Zn dried at RT (b) and TEM image of L₄PS-Zn dried at RT (c), Schematic of L₄PS-Zn depicting a crystalline polyMOF domain embedded within a PS matrix (d) ^[40]

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  3   Two-step synthesis method

  Some coordination complexes such as metal-organic polyhedral (MOPs) are inherently porous. Therefore, a two-step synthesis starting from coordina-tion complexes with polymerization groups can afford crystalline and porous PMCCs. This approach includes two steps: first preparation of coordination complex with polymerization groups and second cross-linking of coordination complexes through homopoly-merization or copolymerization reactions.

  Kitagawa et al. ^[41] in Japan reported the divergent and convergent synthesis of coordination star polymers (CSPs) by using MOPs as a multifunctional core. The great rhombicuboctahedral MOPs as a multifunctional core consists of a total of 24 isophthalic acid ligands interconnected via 12 dicopper paddle wheel clusters. Reversible addition-fragmentation chain transfer polymerization mediated with the MOP led to MOP-star polymers. Atomic force microscope (AFM) images show CSPs exhibit the nanoscale particles.

  Thibonnet et al. ^[42] reported titanium-doped porous polymers obtained from specific Ti-containing monomers with polymerization groups. This free radical co-polymerization reaction affords several titanium-containing polymers, which were dried under supercritical conditions to afford porous organic aerogels. As shown in Fig. 8, the IR spectra reveal that the strong signal at 3 400 cm^-1 for the Ti aerogel may be corresponded to the presence of hydrogen bonded OH groups. Moreover, two carbonyl signals are observed at 1 708 and 1 200 cm^-1 which confirm the existence of Ti carboxylate complexes. The porosity is investigated using N₂ adsorption-desorption isotherms. The BET value of PMCCs was about 454 m²·g^-1. There are mesopores and microporosity characterized through pore size distribution.

  图8 Different porous co-polymers obtained with Ti-complex (a) and IR spectra of a 50/50 Ti1/DVB co-polymer foam and a DVB homopolymer foam (b), N₂ adsorption-desorption isotherms of polymer (c, d) ^[42] Figure8. Different porous co-polymers obtained with Ti-complex (a) and IR spectra of a 50/50 Ti1/DVB co-polymer foam and a DVB homopolymer foam (b), N₂ adsorption-desorption isotherms of polymer (c, d) ^[42]

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  A facile and scalable route to prepare PMCCs were employed by Dai et al. ^[43] The bifunctional 1-vinylimidazole (VIm) with a coordinating site and a polymerizable organic group is introduced as the ligand. Subsequently, the radical polymerization of [Zn(VIm)₄][NO₃]₂ coordination complex is carried out under solvothermal conditions to gain a higher degree of cross-linking. This material exhibits excellent stability in boiling water and can be stable up to 390 ℃ in air. Fig. 9 displays the abundant pores within a large domain of CIN-1. It is observed that mesopores exist side by side among CIN-1 particles. This strategy will inspire a number of stable metal-supported porous polymers by careful selection of ligands, thus opening a new pathway to porous PMCCs.

  图9 Strategy to prepare coordination-supported imidazolate networks (A)and STEM-HAADF images of CIN-1 at 60 kV (B) ^[43] Figure9. Strategy to prepare coordination-supported imidazolate networks (A)and STEM-HAADF images of CIN-1 at 60 kV (B) ^[43]

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  图10 Depiction of polymer imprinting with metal-oxo-hydroxo carboxylate clusters, the adsorption of Fe³⁺ on unimprinted polymer and imprinted polymer ^[44] Figure10. Depiction of polymer imprinting with metal-oxo-hydroxo carboxylate clusters, the adsorption of Fe³⁺ on unimprinted polymer and imprinted polymer ^[44]

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  By using the same synthesis strategy, Walton′s group ^[44] synthesized three new ion-oxo-hydroxo cluster coordinated by vinyl-derivatized carboxylates, [Fe₆O₂(OH)₂(O₂CC(Cl)=CH₂)₁₂(H₂O)₂] (1), [{Fe(O₂CC(Cl)=CH₂)(OMe)₂}₁₀] (2) and [Fe₆O₂(OH)₂(O₂C-Ph-(CH)=CH₂)₁₂(H₂O)₂] (3). Polymerization these Fe-based coordination complexes afford a series of PMCCs. For E-L (non-imprinted copolymer of chloroacrylic acid and egdma) the maximum iron uptake is 1.1 mg·g^-1 of polymer, for E-1 (egdma polymer imprinted with 1) this figure is 1.8 mg·g^-1 of polymer. Hence, the imprinted polymer shows a greater than 60% increase in the amount of iron removed from solution compared to the non-imprinted polymer.

  4   Post-synthetic modification method

  Compared with other porous materials, a great advantage of MOFs is the ability to perform post-synthetic modifications (PSMs). The clear crystal structures and defined pores of MOFs make them as suitable platforms to perform post-synthetic PSMs in MOF crystals without destroying MOFs′ crystallinity. Therefore, if MOFs are functionalized with polymeri-zation groups in their structures, it is possible to employ PSMs method to form crystalline and porous PMCCs.

  图11 Schematic illustration of cross-linking of the organic linkers in MOF and subsequent decomposition to obtain polymer gel (a), Photographs of resulting MOF-templated polymers from various combinations of organic ligands and metal ions (b), Powder X-ray diffraction pattern of a single piece of whole chimera-type hybrid (c) ^[45] Figure11. Schematic illustration of cross-linking of the organic linkers in MOF and subsequent decomposition to obtain polymer gel (a), Photographs of resulting MOF-templated polymers from various combinations of organic ligands and metal ions (b), Powder X-ray diffraction pattern of a single piece of whole chimera-type hybrid (c) ^[45]

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  图12 Schematic images for the CC method using CD-MOF to obtain a cubic gel particle (a), SEM images of CL-CD-MOF and CGP with different sizes (b) ^[46] Figure12. Schematic images for the CC method using CD-MOF to obtain a cubic gel particle (a), SEM images of CL-CD-MOF and CGP with different sizes (b) ^[46]

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  An azide-functionalized terphenyl dicarboxylic acid derivative was selected as the organic ligand for the PSM strategies ^[45]. Starting from dicarboxylic acid ligands, treatment of Zn²⁺, Cu²⁺ and Zr⁴⁺ provid colorless cubic and green truncated octahedral MOF crystals under the solvothermal reactions. The polymer gels (PG) are produced from the transformation of various MOFs via inner cross-linking of the organic linkers in the void space of MOFs, followed by decomposition of the metal coordination. As expected, all crystals are successfully transformed into polymer gels with the same shape as the corresponding MOF, indicating that the PSM method should be applicable to many MOFs systems.

  The uniform cubic gel particles with well-defined edges and square faces using internal cross-linking of the CD-MOF crystals followed by loss of coordinating metal ions ^[46]. The cubic gel particles retain the shape and size of the original CD-MOF crystals, indicating that by controlling the recrystallization conditions a wide range of sizes of CGPs, from millimeters to nanometers, can be produced. Moreover, a variety of polyhedral gel particles from the MOF crystals with controlled polyhedral shapes can be produced.

  5   Characterization and application of coordination polymers

  Similar to the characterization methods for traditional coordination polymers, single crystal and powder X-ray diffraction data can be used to study the crystallinity of PMCCs. For example, the structure of PMCCs in Fig. 2a are firstly determined via the single crystal X-ray diffraction. Furthermore, PXRD is used to confirm that bulky samples possesse the same structure as single crystal. In addition, IR, photolu-minescence spectra (PL) and solid nuclear magnetic resonance (NMR) data can be employed to study whether there are polymer groups formed. As shown in Fig. 13a, the complete polymerization of the [Zn(VIm)₄][NO₃]₂ monomer is indicated by the disapp-earance of the characteristic peak for vinyl group (1 650 cm^-1) in IR spectra ^[43]. Solid state photolumine-scence spectra in Fig. 14 are recorded for 1 (MOF) and 2 (MOPF) after photopolymerization. Compound 1 shows a strong green emission while 2 has a weaker emission which is blue shifted to more strong blue emission which may be due to the loss of extended conjugation upon polymerization ^[35]. The presence of a broad signal at δ 46.5 indicates the formation of the cyclobutane ring in the Solid NMR spectra ^[36] in Fig. 15. SEM, TEM and AFM are widely applied to check the PMCCs particles′ surface morphology, fracture characteristics of cross section and the nanoscale. The SEM images ^[39] in Fig. 5 show that the obtained PMCCs are composed of tiny crystalline nanostructures. TEM images ^[43] in Fig. 9 display the abundant pores within a large domain of CIN-1, wormhole-like mesopores side by side are observed in a high-resolution image, and the apparent pore sizes are in the range of 4~7 nm. AFM spectra ^[41] in Fig. 7 are used to visualize the shape of individual particles of MOP. All particles are clearly shown to possess an individual core that is covered by a polymeric corona.

  图13 IR spectra of [Zn(VIm)₄][NO₃]₂ and CIN-1 (a), formation process of [Zn(VIm)₄][NO₃]₂ to CIN-1 (b) ^[43] Figure13. IR spectra of [Zn(VIm)₄][NO₃]₂ and CIN-1 (a), formation process of [Zn(VIm)₄][NO₃]₂ to CIN-1 (b) ^[43]

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  图14 SCSC transformation from MOF (1) to MOPF (2) by polymerization (a) and their UV spectra (b) ^[35] Figure14. SCSC transformation from MOF (1) to MOPF (2) by polymerization (a) and their UV spectra (b) ^[35]

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  图15 SCSC transformation (a) and its ¹³C CPMAS solid-state NMR spectra (b) ^[36] Figure15. SCSC transformation (a) and its ¹³C CPMAS solid-state NMR spectra (b) ^[36]

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  图7 Schematic diagram of the divergent route for MOP-core CSPs (a) and AFM height image of individual particles of MOP with scale bar=1 μm (b) ^[41] Figure7. Schematic diagram of the divergent route for MOP-core CSPs (a) and AFM height image of individual particles of MOP with scale bar=1 μm (b) ^[41]

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  PMCCs have been reported to possess some promising applications such as catalysis, gas separation and film fabrications. For example, Dai et al. reported that CINs are interesting catalysts for selective oxidations ^[43] . CINs were used in phenol oxidation with water as solvent and H₂O₂ as oxidant. No products are observed in the blank run. However, the CIN-3 with Co²⁺ centers coordinated by imidazole ligand shows a good activity in the oxidation of phenol, and a high turnover frequency (TOF) of 779 h^-1 was achieved. As a solid catalyst, CIN-3 could be easily recovered by centrifugation and reused for at least three cycles with slight loss in efficiency. Hence, CIN-3 could be considered as a promising catalyst in the catalytic oxidation of phenol.

  图16 Catalytic oxidation of phenol by CINs ^[43] Figure16. Catalytic oxidation of phenol by CINs ^[43]

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  Cohen et al. reported that PMCCs could be applied in gas separation ^[38]. The observed selective adsorption of PMCCs can be attributed to a kinetic sieving effect, where the small windows limit the diffusion of larger N₂ molecules into pores resulting in reduced adsorption. Attempts to quantitatively evaluate the CO₂/N₂ and CO₂/CH₄ separation performance at 273 and 298 K for these PMCCs are performed in Fig. 17. The PMCCs can absorb significant amounts of CO₂ at 100 kPa and 298 or 273 K, however low N₂ and methane uptake. The relative high CO₂ sorption but very low N₂ sorption makes these PMCCs as promising materials for CO₂/N₂ separation.

  图17 CO₂, CH₄ and N₂ sorption isotherms at 273 K (a) and CO₂, CH₄ and N₂ sorption isotherms at 298 K for polyMOFs (b) Figure17. CO₂, CH₄ and N₂ sorption isotherms at 273 K (a) and CO₂, CH₄ and N₂ sorption isotherms at 298 K for polyMOFs (b)

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  Except the above application, PMCCs also are easy to fabricate films as shown in Fig. 18. Cohen et al. reported that at a low temperature, rather than forming spheroidal structures, Zn-pbdc-7a and Zn-pbdc-8a produce crystalline films, showing an intergrown network of crystallites. The films are about 20 μm thick. Such films may prove useful for small molecule and gas separations ^[37].

  图18 Film morphology of Zn-pbdc-7a (a) and Zn-pbdc-8a (b) Figure18. Film morphology of Zn-pbdc-7a (a) and Zn-pbdc-8a (b)

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  6   Summary and outlook

  In this review article, we have discussed four approaches how to construct polymer-metal coordina-tion complexes (PMCCs) with good crystalline and high porosity. We also display the characterization methods of PMCCs. Although PMCCs are in the process of rapid development, there are still some challenges and potential chances. For the first approach, the limited numbers of coordination complexes for realizing the single crystal to single crystal manner is a big challenge in the research. Therefore, design coordination complexes with novel topologies suitable for photo-polymerization is of great significance in the future research. During the transformation process, crystals are easy to lose their crystallinity. So how to control the completeness of polymerization and retain the crystallinity of PMCCs is deserved to explore. For the second approach, it is difficult to synthesize crystalline PMCCs because the organic chain polymers are mostly amorphous, flexible and non-porous. Finding appropriate polymer ligands react directly with metal ions is extremely urgent. For the third approach, finding right coordination comp-lexes with polymerization groups is very important and the conditions for homopolymerization or copoly-merization of the complex is also needed to be explored to find the appropriate condition reactions. For the fourth approach, how to control the reaction condition to retain the crystallinity of coordination polymers is the key in research. These techniques will enable the as-yet unexplored precise structural control of PMCCs on the molecular, which are advanced materials for novel properties and applications discovered in the future.

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  Figure 1  SCSC transformation from a MOF to a PMCC under UV light by polymerization and the diagram of the polymer (a), photographs of crystals under room light and UV-365 nm light (b) ^[35]

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  Figure 2  Reversible polymerization by [2+2] photo-cycloaddition under UV lamp and depolymerization on heating (a), PXRD patterns for as synthesized, after UV-irradiation and after heating (b) ^[36]

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  Figure 3  IRMOF derivatives construct from an H₂bdc ligand derivative, a cross-linked H₂bdc ligand, and a polymeric H₂bdc polymer ligand with Zn²⁺ (a), N₂ sorption isotherms for polyMOFs (top) and CO₂ adsorption isotherms at 298 K (bottom) (b) ^[37]

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  Figure 4  Design concept for creating a polyMOF analogue of MOF via replacing dangling groups by polymer chains (a), N₂ sorption and CO₂ sorption isotherms for polyMOFs (b) ^[38]

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  Figure 5  PXRD patterns, SEM images and N₂ sorption isotherms of polyMOF prepared from different polymer ligands (a~d) ^[39]

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  Figure 6  SEM images of L_4-Zn (a), L₄PS-Zn dried at RT (b) and TEM image of L₄PS-Zn dried at RT (c), Schematic of L₄PS-Zn depicting a crystalline polyMOF domain embedded within a PS matrix (d) ^[40]

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  Figure 8  Different porous co-polymers obtained with Ti-complex (a) and IR spectra of a 50/50 Ti1/DVB co-polymer foam and a DVB homopolymer foam (b), N₂ adsorption-desorption isotherms of polymer (c, d) ^[42]

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  Figure 9  Strategy to prepare coordination-supported imidazolate networks (A)and STEM-HAADF images of CIN-1 at 60 kV (B) ^[43]

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  Figure 10  Depiction of polymer imprinting with metal-oxo-hydroxo carboxylate clusters, the adsorption of Fe³⁺ on unimprinted polymer and imprinted polymer ^[44]

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  Figure 11  Schematic illustration of cross-linking of the organic linkers in MOF and subsequent decomposition to obtain polymer gel (a), Photographs of resulting MOF-templated polymers from various combinations of organic ligands and metal ions (b), Powder X-ray diffraction pattern of a single piece of whole chimera-type hybrid (c) ^[45]

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  Figure 12  Schematic images for the CC method using CD-MOF to obtain a cubic gel particle (a), SEM images of CL-CD-MOF and CGP with different sizes (b) ^[46]

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  Figure 13  IR spectra of [Zn(VIm)₄][NO₃]₂ and CIN-1 (a), formation process of [Zn(VIm)₄][NO₃]₂ to CIN-1 (b) ^[43]

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  Figure 14  SCSC transformation from MOF (1) to MOPF (2) by polymerization (a) and their UV spectra (b) ^[35]

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  Figure 15  SCSC transformation (a) and its ¹³C CPMAS solid-state NMR spectra (b) ^[36]

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  Figure 7  Schematic diagram of the divergent route for MOP-core CSPs (a) and AFM height image of individual particles of MOP with scale bar=1 μm (b) ^[41]

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  Figure 16  Catalytic oxidation of phenol by CINs ^[43]

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  Figure 17  CO₂, CH₄ and N₂ sorption isotherms at 273 K (a) and CO₂, CH₄ and N₂ sorption isotherms at 298 K for polyMOFs (b)

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  Figure 18  Film morphology of Zn-pbdc-7a (a) and Zn-pbdc-8a (b)

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