Coordination Polymers based on calixarene derivatives: Structures and properties

Dual Brønsted acidic-basic function immobilized on the 3D mesoporous polycalix [4]resorcinarene: As a highly recyclable catalyst for the synthesis of spiro acenaphthylene/indene heterocycles

In this study, a novel dual Brønsted acidic-basic nano-scale porous organic polymer catalyst, PC4RA@SiPr-Pip-BuSO3H, was synthesized through various steps: preparation of a 3D network of polycalix, modification with (3-chloropropyl)-trimethoxysilane, then functionalization of polymer with piperazine and n-butyl sulfonic acid under the provided conditions. The catalyst characterization was performed by FT-IR, TGA, EDS, elemental mapping, PXRD, TEM, and FE-SEM analyses, confirming high chemical stability, activity, recoverability, and excellent covalent anchoring of functional groups. So, the designed catalyst was utilized for preparing spiro-acenaphthylene and amino-spiroindene heterocycles, providing good performance with a high yield of the corresponding products. Accordingly, this catalyst can be used in different organic transformations. Necessary experiments were conducted for the recyclability test of the polymeric catalyst, and the results showed the PC4RA@SiPr-Pip-BuSO3H catalyst can be reused 10 times without any decrease in its activity or quality with excellent stability. The structure of resultant spiro heterocycles was confirmed using 1H NMR, 13C NMR, and FT-IR.

Applications of supramolecular assemblies in drug delivery and photodynamic therapy

One of the world's serious health challenges is cancer. Anti-cancer agents delivered to normal cells and tissues pose several problems and challenges. In this connection, photodynamic therapy (PDT) is a minimally invasive therapeutic technique used for selectively destroying malignant cells while sparing the normal tissues. Development in photosensitisers (PSs) and light sources have to be made for PDT as a first option treatment for patients. In the pursuit of developing new attractive molecules and their formulations for PDT, researchers are working on developing such type of PSs that perform better than those being currently used. For the widespread clinical utilization of PDT, effective PSs are of particular importance. Host-guest interactions based on nanographene assemblies such as functionalized hexa-cata-hexabenzocoronenes, hexa-peri-hexabenzocoronenes and coronene have attracted increasing attention owing to less complicated synthetic steps and purification processes (gel permeation chromatography) during fabrication. Noncovalent interactions provide easy and facile approaches for building supramolecular PSs and enable them to have sensitive and controllable photoactivities, which are important for maximizing photodynamic effects and minimizing side effects. Various versatile supramolecular assemblies based on cyclodextrins, cucurbiturils, calixarenes, porphyrins and pillararenes have been designed in order to make PDT an effective therapeutic technique for curing cancer and tumours. The supramolecular assemblies of porphyrins display efficient electron transfer and fluorescence for use in bioimaging and PDT. The multifunctionalization of supramolecular assemblies is used for designing biomedically active PSs, which are helpful in PDT. It is anticipated that the development of these functionalized supramolecular assemblies will provide more fascinating advances in PDT and will dramatically expand the potential and possibilities in cancer treatments.

Thiacalix[4]arene-protected alkynyl Agn (n = 9, 18) nanoclusters: syntheses, structural characterizations, photocurrent responses and fluorescence properties

Two thiacalix[4]arene-protected silver(I) alkynyl nanoclusters, [Na2(H2O)2][Ag9(TC4A)(tBuCC)4(CH3OH)2(SbF6)0.5(OH)2.5]·3.5H2O·CH3OH (1, abbreviated as Ag9) and [Ag9(TC4A)(tBuCC)4(CF3COO)]2·4CH3OH (2, abbreviated as Ag18), were synthesized by the reaction of [tBuCCAg]n, p-tert-butylthiacalix[4]arene (H4TC4A), NaBH4, and AgSbF6 or CF3COOAg in the mixed solvent of methanol-trichloromethane-toluene under solvothermal conditions, respectively. Driven by SbF6- and CF3COO- with different coordination properties, the structural unit [Ag9(TC4A)(tBuCC)4]+ in both the compounds migrated in different modes, accompanied by distinct Ag⋯Ag distances. Ag9 and Ag18 exhibit similar UV-Vis absorption and diffuse reflection spectra along with contrary tendency between photocurrent responses and solid-state fluorescence. The solution stability of Ag9 and Ag18 was demonstrated by 1H NMR and MALDI-TOF mass spectrometry. The fluorescence responses of Ag9 and Ag18 towards different organic molecules were also investigated, which indicated that the polarity of solvent has a certain effect on the emission intensities of Ag9 and Ag18. This study provides a positive guide for the controlled synthesis and further study of the structure-activity relationship of thiacalix[4]arene-protected silver alkynyl nanoclusters.

Tungstic acid-functionalized polycalix[4]resorcinarene as a cavity-containing hyper-branched supramolecular and recoverable acidic catalyst in 4H-pyran synthesis

In this study, tungstic acid immobilized on polycalix[4]resorcinarene, PC4RA@SiPr-OWO₃H, as a mesoporous acidic solid catalyst was synthesized and investigated for its catalytic activity. Polycalix[4]resorcinarene was prepared via a reaction between formaldehyde and calix[4]resorcinarene, and then the resulting polycalix[4]resorcinarene was modified using (3-chloropropyl)trimethoxysilane (CPTMS) to obtain polycalix[4]resorcinarene@(CH₂)₃Cl that was finally functionalized with tungstic acid. The designed acidic catalyst was characterized by various methods including FT-IR spectroscopy, energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), elemental mapping analysis and transmission electron microscopy (TEM). The catalyst efficiency was evaluated via the preparation of 4H-pyran derivatives using dimethyl/diethyl acetylenedicarboxylate, malononitrile, and beta-carbonyl compounds, confirmed by FT-IR spectroscopy and ¹H and ¹³C NMR spectroscopy. The synthetic catalyst was introduced as a suitable catalyst with high recycling power in 4H-pyran synthesis.

Atomically accurate structural tailoring of thiacalix[4]arene-protected copper(II)-based metallamacrocycles

Accurate manipulation of ligands at specific sites in robust clusters is attractive but difficult, especially for those ligands that coordinate in intricate binding patterns. By linking the shuttlecock-like {Cu₄(μ₄-Cl)TC4A} motif and the phenylphosphate (PhPO₃^2-) ligand, we elaborately design and synthesize two Cu(II)-thiacalix[4]arene metallamacrocycles (MMCs), namely Cu₁₂L₃ and Cu₁₆L₄, which have regular triangular and quadrilateral topologies, respectively. While keeping the core intact, the Cl^- and PhPO₃^2- in those two MMCs, which coordinated in a μ₄-bridging fashion, can be accurately substituted with salicylate ligands. Theoretical calculations have been carried out to reveal the effect of ligand tailoring on the electronic structure of clusters. Structural regulation can affect the catalytic activity of these clusters, which has been verified by using the clusters as catalysts for selective sulfide oxidation.

DFT study of the conformation, hydrogen bonds, IR, Raman, and NMR spectra of 1,3-disubstituted p-tert-butylthiacalix[4]arenes

CONTEXT

The molecular design of spatially preorganized molecules is one of the critical issues in organic chemistry. Molecular recognition and multipoint binding define them. They organize nanoscale assemblies and devices and stably form host-guest inclusion complexes. Not only is this kind of research important in theory but it also has applications. They are used to create the basic elements of sensory devices: elements of cellular electronics, functional nanofilms and coatings, molecular switches, etc. Thiacalix[4]arenes are a useful molecular platform for constructing a wide range of preorganized receptor structures. This research aims to examine the structure and spectra of distally substituted para-tert-butylthiacalix[4]arene aliphatic (C1) and aromatic (C2) esters. The comparison of the spectra of C1, C2, and C3 makes it possible to reveal the structures and H-bonds of these compounds. The structures and H-bonds of these compounds can be seen by analyzing the spectra of C1, C2, and C3. Calculations were made for the spectra of various C1 and C2 molecule conformations. The most stable conformation for C1 and C2 molecules is a distorted cone 2 (DC2) with the same ester group orientation. The pinched cone (PC) conformation is the most unstable. Thiacalixarene molecules' cavities shrink from 3.61 to 3.57 Å when aromatic ester groups take the place of aliphatic ester groups. Two OH groups are linked to an oxygen atom in the DC1 and DC2 conformations of the C1 and C2 molecules. H-bonds in C1 and C2 molecules affect the supramolecular characteristics of these molecules. A drop in ionization energy and increases in electron affinity, chemical potential, softness, electrophilicity index, and dipole moment occur when aliphatic esters are replaced with aromatic ones.

METHODS

Disubstituted aliphatic and aromatic esters' IR, Raman, and NMR spectra have been investigated. The DFT/B3LYP/6-311G(d,p) method and the GAUSSIAN 09W software were used to determine the vibrational spectra of molecules and optimize their geometry. A gauge-independent (GIAO) approach was used to determine chemical shifts in the NMR spectra with respect to tetramethylsilane.

Sulfonate-modified calixarene-based porous organic polymers for electrostatic enhancement and efficient rapid removal of cationic dyes in water

Developing of fast and efficient adsorbents for removal of low concentration refractory organics in water is significant. Herein, a novel calix[4]arene-based porous organic polymer CaPy is constructed through Sonogashira-Hagihara cross-coupling polycondensation. The strong polar sulfonate is further anchored onto the polymer skeleton of CaPy and three sulfonate-modified anionic polymers CaPy-S1, CaPy-S2, and CaPy-S3 were obtained and fully characterized. The adsorption isotherms showed that the maximum adsorption capacities of CaPy, CaPy-S1, CaPy-S2, and CaPy-S3 toward methylene blue (MB) were 270, 1454, 558 and 1381 mg g^-1, whereas those for Rhodamine B (RhB) were 183, 2653, 1132, and 1796 mg g^-1, respectively. The maximum adsorption capacity toward RhB was the highest reported vale among the currently used synthetic adsorbents. In addition, the pseudo-second-order rate constants of CaPy, CaPy-S1, CaPy-S2, and CaPy-S3 toward MB were 0.00572, 0.488, 2.24, and 0.192 g mg^-1 min^-1, respectively, and those toward RhB were 0.000234, 0.138, 0.0819, and 0.203 g mg^-1 min^-1, respectively. The pseudo-second-order rate constant of CaPy-S2 toward MB was 2.24 g mg^-1 min^-1 indicating one of the highest adsorption speeds. The activation energy of CaPy-S1 for RhB and MB were 121 and 109 kJ mol^-1, respectively, demonstrating that the adsorption of both dyes on CaPy-S1 was chemisorption process. Further, the obtained values of Gibbs free energy were negative, revealing that the adsorption process was spontaneous. This work provides an effective approach for improving adsorption performance via post-modification.

Organo-macrocycle-containing hierarchical metal-organic frameworks and cages: design, structures, and applications

Developing hierarchical ordered systems is challenging. Using organo-macrocycles to construct metal-organic frameworks (MOFs) and porous coordination cages (PCCs) provides an efficient way to obtain hierarchical assemblies. Macrocycles, such as crown ethers, cyclodextrins, calixarenes, cucurbiturils, and pillararenes, can be incorporated within MOFs/PCCs and they also endow the resultant composites with enhanced properties and functionalities. This review summarizes recent developments of organo-macrocycle-containing hierarchical MOFs/PCCs, emphasizing applications and structure-property relationships of these hierarchically porous materials. This review provides insights for future research on hierarchical self-assembly using macrocycles as building blocks and functional ligands to extend the applications of the composites.

Synthesis of a Zirconium Complex of an N,O-type p-tert-Butylcalix[4]arene and Its Application in Some Multicomponent Reactions

The synthesis and characterization of a new octahedral Zr(IV) complex of oxygen-depleted N,O-type calixarene ligand comprising two distal-functionalized pyrazole rings have been reported. The cone shape and structure of the prepared complex were confirmed univocally by single-crystal X-ray diffraction and NMR studies. The Zr metal lies at 2.091 Å from the plane of the calixarene ring. This complex has been utilized as an efficient catalyst for the synthesis of Biginelli adducts, bis(indolyl)methanes, and coumarins. This complex (Cl₂Zr-calixarene) showed superior activity for these multicomponent reactions in comparison to the corresponding Ti(IV) and Zn(II) analogues. Ferrocene-appended bis(indolyl)methane, prepared using this catalyst, was also evaluated for its anticancer activity against the A-172 cell line.

New Calix[4]arene—Fluoresceine Conjugate by Click Approach—Synthesis and Preparation of Photocatalytically Active Solid Lipid Nanoparticles

New fluorescent systems for photocatalysis, sensors, labeling, etc., are in great demand. Amphiphilic ones are of special interest since they can form functional colloidal systems that can be used in aqueous solutions. A new macrocycle platform for click chemistry and its adduct with o-propargylfluoresceine was synthesized and characterized using modern physical techniques. Nanosized solid lipid nanoparticles (SLNs) from the calixarene—fluoresceine adduct were synthesized through the solvent injection technique and well-characterized in the solution and in solid state using light-scattering and microscopy methods. The maximum fluorescence intensity of the SLNs was found to be in the pH range from 7 to 10. The Förster resonance energy transfer (FRET) efficiency from SLNs to rhodamine 6g was found to be 97.8%. Finally, pure SLNs and the FRET system SLNs—Rh6G were tested in model photocatalytic ipso oxidative hydroxylation of phenylboronic acid under blue LED light. The SLNs—Rh6G system was found to be the best, giving an almost qualitative phenol yield, which was shown by HPLC-UV analysis.

Porous nickel and cobalt hexanuclear ring-like clusters built from two different kind of calixarene ligands – new molecular traps for small volatile molecules

The formation and structural analysis of porous hexanuclear ring-like cluster complexes built from two different kind of calixarene ligands is presented, together with their stability and vapor solvent sorption properties.

Halogen-bonded architectures of multivalent calix[4]arenes

A 2D halogen bonded network of calixarene macrocycles was obtained by co-crystallization of a 1,3-alternate calix[4]arene as a tetravalent XB donor with a bidentate XB acceptor.

Impact of flexible succinate connectors on the formation of tetrasulfonylcalix[4]arene based nano-sized polynuclear cages: structural diversity and induced chirality study

The formation of three types of supramolecular coordination cages is described. Tetrasulfonylcalixarene, combined with metallic salts (Ni, Co and Zn) and the flexible succinate ligand, led to cages. H bonded induced chirality was observed for both isomorphous cages.

Study of the conformation and hydrogen bonds of the p-tetrasulfonatothiacalix[4]arene pentasodium salt by vibrational spectroscopy and DFT

The vibrational spectra of the p-tetrasulfonatothiacalix[4]arene pentasodium salt (TCAS) and tert-butylthiacalix[4]arene (BuTCA) were studied. Comparison of the TCAS and BuTCA IR spectra allows us to isolate the bands of tert-butyl and sulfonate groups. Geometry, IR and Raman spectra were calculated for conformation cone, partial cone, 1,2-, and 1,3-alternate. The most stable conformation of the TCAS is the cone. Characteristic bands were determined for each of the possible conformations. In the case of the TCAS molecule, four ions of sodium are coordinated with the oxygen atoms of sulfonate groups, and the fifth ion interacts with the oxygen and sulfur atoms of the macrocycle. Under the influence of sodium ions, the distribution of electron density in the TCAS molecule and its ability to supramolecular interactions change.

Binding of a TlCl Entity by a Tetragold Tetramercaptothiacalixarene Metalloligand via Metallophilic Interactions

The successive auration of p-tert-butyltetramercaptotetrathiacalix[4]arene, H₄ (MTC[4]), with gold(I) phosphine units was investigated. Through deprotonation with NaOMe, followed by salt metathesis reactions with (PR₃ )AuCl (R=Me, Ph) complexes with two and three [(PR₃ )Au]⁺ moieties could be prepared and isolated, namely [(Ph₃ PAu)₂ H₂ (MTC[4])] and [(Me₃ PAu)₃ H(MTC[4])]. In [(Me₃ PAu)₃ H(MTC[4])] two gold atoms already come close enough to undergo aurophilic interactions. To introduce a fourth [(PR₃ )Au]⁺ entity TlOEt had to be used for the deprotonation, which led to the finding that four gold atoms organised by the (MTC[4])^4- coordination platform are able to bind and stabilize a TlCl entity, yielding [(Me₃ PAu)₄ TlCl(MTC[4])]. As evidenced by structural and theoretical investigations the binding occurs through strong metallophilic interactions, which lead to photoluminescence at low temperatures.

Switching Ion Binding Selectivity of Thiacalix[4]arene Monocrowns at Liquid-Liquid and 2D-Confined Interfaces

Understanding the interaction of ions with organic receptors in confined space is of fundamental importance and could advance nanoelectronics and sensor design. In this work, metal ion complexation of conformationally varied thiacalix[4]monocrowns bearing lower-rim hydroxy (type I), dodecyloxy (type II), or methoxy (type III) fragments was evaluated. At the liquid–liquid interface, alkylated thiacalixcrowns-5(6) selectively extract alkali metal ions according to the induced-fit concept, whereas crown-4 receptors were ineffective due to distortion of the crown-ether cavity, as predicted by quantum-chemical calculations. In type-I ligands, alkali-metal ion extraction by the solvent-accessible crown-ether cavity was prevented, which resulted in competitive Ag⁺ extraction by sulfide bridges. Surprisingly, amphiphilic type-I/II conjugates moderately extracted other metal ions, which was attributed to calixarene aggregation in salt aqueous phase and supported by dynamic light scattering measurements. Cation–monolayer interactions at the air–water interface were monitored by surface pressure/potential measurements and UV/visible reflection–absorption spectroscopy. Topology-varied selectivity was evidenced, towards Sr²⁺ (crown-4), K⁺ (crown-5), and Ag⁺ (crown-6) in type-I receptors and Na⁺ (crown-4), Ca²⁺ (crown-5), and Cs⁺ (crown-6) in type-II receptors. Nuclear magnetic resonance and electronic absorption spectroscopy revealed exocyclic coordination in type-I ligands and cation–π interactions in type-II ligands.

Metallo-Supramolecular Coordination Polymers Based on Amidopyridine Derivatives of Pillar[5]arene and Cu(II) and Pd(II) Cations: Synthesis and Recognition of Nitroaromatic Compounds

Decasubstituted pillar[5]arenes containing amidopyridine fragments have been synthesized for the first time. As was shown by UV-vis spectroscopy, the pillar[5]arenes with p-amidopyridine fragments form supramolecular associates with Cu(II) and Pd(II) cations in methanol in a 2:1 ratio. Using a sol-gel approach these associates are transformed into metallo-supramolecular coordination polymers (supramolecular gels) which were characterized as amorphous powders by scanning electron microscopy (SEM) and dynamic light scattering (DLS). The powders are able to selectively adsorb up to 46% of nitrophenols from water and were incorporated into an electrochemical sensor to selectively recognize them in aqueous acidic solution.

Coordination polymers with embedded recognition sites: lessons from cyclotriveratrylene-type ligands

Coordination polymers with molecular recognition sites are assembled using cyclotriveratrylene ligands. Many show differential guest-spaces with host and lattice sites available, however common host–guest and self-inclusion motifs can block sites.

Non-traditional thermal behavior of Co(ii) coordination networks showing slow magnetic relaxation

Three new Co(ii) coordination polymers show the DC magnetic data consistent with the S = 3/2 spin system with large zero-field splitting D > 0, which was confirmed by HF EPR and FIRMS measurements.

Self-assembly of cuprous iodide cluster-based calix[4]resorcinarenes and photocatalytic properties

Cluster-based complexes 1 and 2 with [Cu6I5] and [Cu8I8] polynuclear motifs were constructed via a conformation-adaptive self-assembly strategy, respectively. Two Cu(i) complexes exhibited photocatalytic activity to the CuAAC reaction in water solution.

Recent progress to construct calixarene-based polymers using covalent bonds: synthesis and applications

The combination of supramolecular chemistry and polymer sciences creates a great possibility to afford calixarene-based polymers offering unique features and applications. The enhancement of calixarene's versatility in this manner has made chemists better able to achieve different objectives in host-guest chemistry. The calixarene-based polymers can be divided into covalent polymers and supramolecular polymers regarding the interactions. Although there are several studies available on the calixarene-based supramolecular polymers, there is a paucity of studies on the calixarene-based covalent polymers. In this paper, the most recent developments and applications of the calixarene-based covalent polymers in the last two decades have been reviewed. We have particularly focused on the polymers, including those where the calixarene molecules have been used as macromonomers and polymerize through covalent bonds. Moreover, covalent polymers or solid supports functionalized with calixarenes are highlighted as well.

Formation of Unsymmetrical Trinuclear Metallamacrocycles Based on Two Different Cone Calix[4]arene Macrocyclic Rings

A combination of tetrasulfonylcalix[4]arene (3-4H) together with a calix[4]arene dicarboxylate derivative 2-4H led, in the presence of MII(NO3)2 (M = Co, Ni, Zn), to the formation of three novel isostructural metallomacrocycles of formula [M3(DMF)2(μ3-H2O)-(2-2H)-3]. The structure of the prepared coordination compounds was studied in the solid state using single crystal/powder X-ray diffraction studies. The X-ray diffraction on single crystal revealed that the structure of the obtained supramolecular complexes is composed of a trinuclear metallic cluster [M3]+6 held between one di-deprotonated molecule of (2-2H)2− offering two carboxylate groups for binding metal cations and one tetra-deprotonated compound 34−, where four oxygen atoms, belonging to four deprotonated phenolic moieties and three oxygen atoms coming from three SO2 groups, are coordinated with the cluster core. Thus, an example of an easily reproducible molecular recognition pattern involving two different types of calix[4]arene based ligands, displaying different coordination moieties, and trinuclear metallic clusters, is reported here. In addition, it has been shown that the cone moieties of the calixarene also encapsulate solvent molecules.

Three thiacalix[4]arene-based Cu(i) coordination polymers: catalytic activities for azide-alkyne cycloaddition reactions and luminescence properties

Three new coordination polymers, [Cu₂(CN)(L)(OCH₃)]·CH₃OH·3H₂O (1), [Cu₃(Br)₃(L)] (2) and [Cu(I)(L)]·1.5H₂O (3), have been solvothermally prepared by reacting L (5,11,17,23-tetra-tert-butyl-25,26,27,28-tetra[(3-pyridylmethyl)oxy]-2,8,14,20-tetrathiacalix[4]arene) with Cu(i) halide. 1 and 2 exhibit layers. 3 displays a chain, a supramolecular layer constructed by hydrogen bonds. The performance of 1-3 was examined as heterogeneous catalysts for azide-alkyne cycloaddition reactions. Most strikingly, 1 and 2 show predominant efficiency with high regioselectivity and excellent recyclability. Remarkably, solids 1-3 all have luminescence characteristics under irradiation with a UV lamp.

Mixed Tb/Dy coordination ladders based on tetra(carboxymethyl)thiacalix[4]arene: a new avenue towards luminescent molecular nanomagnets

The macrocyclic ligand calix[4]arene (L1) and its sulphur-containing analogue thia[4]calixarene (L2) are promising precursors for functional molecular materials as they offer rational functionalization with various organic groups. Here, we present the first example of lanthanide-based coordination polymers built from the macrocyclic thiacalix[4]arene backbone bearing four carboxylic moieties, namely, ligand H₄L3. The combination of H₄L3 with the Tb³⁺ and Dy³⁺ cations led to the formation of 1D ladder-type coordination polymers with the formula [Ln^IIIHL3DMF₃]·(DMF) (where DMF = dimethylformamide and Ln = Tb or Dy, denoted as HL3–Tb and HL3–Dy), which resulted from the coordination of the lanthanide cations with the partially deprotonated ligand HL3³⁻ that behaved as a T-shape connector. The coordination sphere around the metal was completed by the coordinated DMF solvent molecules. By combining both Tb³⁺ and Dy³⁺ cations, isostructural heterobimetallic solid solutions HL3–Tb_1−xDy_x were also prepared. HL3–Tb and HL3–Dy showed visible light photoluminescence originating from the f–f electronic transitions of pale green emissive Tb³⁺ and pale yellow emissive Dy³⁺ with efficient sensitization by the functionalized thia[4]calixarene ligand HL3. In the HL3–Tb_1−xDy_x solid solutions, the Tb/Dy ratio governed both the emission colour as well as the emission quantum yield, which reached even 28% at room temperature for HL3–Tb. Moreover, HL3–Dy exhibited a slow magnetic relaxation effect related to the magnetic anisotropy of the dodecahedral Dy³⁺ complexes, which were well isolated in the crystal lattice by expanded organic spacers.

The single crystals of the two isostructural Tb³⁺- and Dy³⁺-based coordination polymers (HL3–Tb and HL3–Dy) were structurally characterized, and their photophysical properties were investigated, together with their corresponding solid solutions.

Metalloporphyrinic metal-organic frameworks: Controlled synthesis for catalytic applications in environmental and biological media

Recently, as a new sub-family of porous coordination polymers (PCPs), porphyrinic-MOFs (Porph-MOFs) with biomimetic features have been developed using porphyrin macrocycles as ligands and/or pillared linkers. The control over the coordination of the porphyrin ligand and its derivatives however remains a challenge for engineering new tunable Porph-MOF frameworks by self-assembly methods. The key challenges exist in the following respects: (i) collapse of the large open pores of Porph-MOFs during synthesis, (ii) deactivation of unsaturated metal-sites (UMCs) by axial coordination, and (iii) the tendency of both coordinated moieties (at peripheral meso- and beta-carbon sites) and the N₄-pyridine core to coordinate with metal cations. In this respect, this review covers the advances in the design of Porph-MOFs relative to their counterpart covalent organic frameworks (Porph-COFs). The potential utility of custom-designed porphyrin/metalloporphyrins ligands is highlighted. Synthesis strategies of Porph-MOFs are also illustrated with modular design of hybrid guest@host composites (either Porph@MOFs or guest@Porph-MOFs) with exceptional topologies and stability. This review summarizes the synergistic benefits of coordinated porphyrin ligands and functional guest molecules in Porph-MOF composites for enhanced catalytic performance in various redox applications. This review shed lights on the engineering of new tunable hetero-metals open active sites within (metallo)porphyrin-MOFs as out-of-the-box platforms for enhanced catalytic processes in chemical and biological media.