Multi-Stimuli-Responsive Metallogel Molded from a Pd2L4-Type Coordination Cage: Selective Removal of Anionic Dyes

Tunable Metallogels Based on Bifunctional Ligands: Precursor Metallogels, Spinel Oxides, Dye and CO2 Adsorption

A semisolid gel material is a gift of serendipity via various chemical interactions, and metal incorporation (metallogels) imparts diverse functional properties. In this work, we have synthesized four metallogels from tetrapodal and hexapodal carboxylic acid/amide-based low-molecular-weight gelators with Ni(II) and Cu(II) salts. These metallogels can be tuned to be a low-temperature precursor of porous spinel oxides. These xerogels exhibit impressive water soluble dye and carbon dioxide adsorption, which coupled with the tunability and facile synthesis of porous spinel oxides underscores their potential in environmental remediation and energy applications.

Novel Approach to Generate a Self-Deliverable Ru(II)-Based Anticancer Agent in the Self-Reacting Confined Gel Space

Finding the most effective method for cancer treatment is one of the thought-provoking tasks. Drug delivery by collapsing of metallogel to the cancer cell is an appealing way out. Cancer cells have an acidic environment due to excessive accumulation of lactic acid. In this work, the novel G5 gelator with a strategically free carboxylic acid arm has been designed and fabricated and characterized by several spectroscopic and microscopic techniques. These experiments suggest the formation of an ordered supramolecular gel with clover-leaf-like morphology. Mechanical properties from rheological measurements suggest the viscoelastic nature of the gel. Furthermore, we have obtained crystals of G5 from the pure dimethyl sulfoxide solution, whereas gelation gets induced by addition of water. This G5 gelator loses its gelation capability once the carboxylate is esterified by layering with methanol, which furnished the crystals of Me-G5' (G5' = G5-H). Further, the G5 gelator is used for the formation of ruthenium metallogel. Interestingly, we obtained the monomeric species [Ru(G5')(η⁶-p-cymene)Cl] [Ru(II)G5] only in confined gel space upon addition of a [Ru₂(η⁶-p-cymene)₂Cl₄] dimer to G5. The Ru(II)G5 metallogel has an inherent anticancer property with an IC₅₀ value of 10.53 μM for the A549 cancer cell line. Treatment of the Ru(II)G5 metallogel by lactic acid for mimicking the acidic environment of the malignant cell results in collapsing of the gel by releasing the ruthenium metal ion. This released ruthenium ion binds with the lactic acid derivative making the gelator G5 free and producing a new compound Ru(II)L, which has also shown the anticancer property. The molecular docking study revealed that the released G5 could interact with a monocarboxylate transporter to disrupt the lactate transport chain, which might induce apoptosis.

One-step synthesis of Cu(II) metal-organic gel as recyclable material for rapid, efficient and size selective cationic dyes adsorption

Efficient removal of non-biodegradable and hazardous dyes from wastewater remains a hot research topic. Herein, a rationally designed a Cu(II)-based metal-organic gel (Cu-MOG) with a nanoporous 3D network structure prepared via a simple one-step mixing method was successfully employed for the removal of cationic dyes. The Cu-MOG exhibited high efficiency, with an adsorption capacity of up to 650.32 mg/g, and rapid adsorption efficiency, with the ability to adsorb 80% of Neutral Red within 1 min. The high adsorption efficiency was attributed to its large specific surface area, which enabled it to massively bind cationic dyes through electrostatic interaction, and a nanoporous structure that promoted intra-pore diffusion. Remarkably, the Cu-MOG displayed size-selective adsorption, based on adsorption studies concerning dyes of different sizes as calculated by density functional theory. Additionally, the adsorption performance of the Cu-MOG still maintained removal efficiency of 100% after three regeneration cycles. These results suggested that the Cu-MOG could be expected to be a promising and competitive candidate to conveniently process wastewater.

Embedding and Positioning of Two FeII4 L4 Cages in Supramolecular Tripeptide Gels for Selective Chemical Segregation

An unreported d,l-tripeptide self-assembled into gels that embedded FeII4 L4 metal-organic cages to form materials that were characterized by TEM, EDX, Raman spectroscopy, rheometry, UV/Vis and NMR spectroscopy, and circular dichroism. The cage type and concentration modulated gel viscoelasticity, and thus the diffusion rate of molecular guests through the nanostructured matrix, as gauged by 19 F and 1 H NMR spectroscopy. When two different cages were added to spatially separated gel layers, the gel-cage composite material enabled the spatial segregation of a mixture of guests that diffused into the gel. Each cage selectively encapsulated its preferred guest during diffusion. We thus present a new strategy for using nested supramolecular interactions to enable the separation of small molecules.

Design of a double-decker coordination cage revisited to make new cages and exemplify ligand isomerism

The complexation study of cis-protected and bare palladium(II) components with a new tridentate ligand, i.e., pyridine-3,5-diylbis(methylene) dinicotinate (L1) is the focus of this work. Complexation of cis-Pd(tmeda)(NO₃)₂ with L1 at a 1:1 or 3:2 ratio produced [Pd(tmeda)(L1)](NO₃)₂ (1a). The reaction mixture obtained at 3:2 ratio upon prolonged heating, produced a small amount of [Pd₃(tmeda)₃(L1)₂](NO₃)₆ (2a). Complexation of Pd(NO₃)₂ with L1 at a 1:2 or 3:4 ratios afforded [Pd(L1)₂](NO₃)₂ (3a) and [(NO₃)₂@Pd₃(L1)₄](NO₃)₄ (4a), respectively. The encapsulated NO₃^– ions of 4a undergo anion exchange with halides (F^–, Cl^– and Br^– but not with I^–) to form [(X)₂@Pd₃(L1)₄](NO₃)₄5a–7a. The coordination behaviour of ligand L1 and some dynamic properties of these complexes are compared with a set of known complexes prepared using the regioisomeric ligand bis(pyridin-3-ylmethyl)pyridine-3,5-dicarboxylate (L2). Importantly, a ligand isomerism phenomenon is claimed by considering complexes prepared from L1 and L2.

Palladium-Based Metal-Ligand Assemblies: The Contrasting Behavior upon Addition of Pyridine or Acid

The stability of five different [Pd _n(N-donor) _m]^{2 n+} assemblies was examined by performing disassembly experiments with pyridine and with trifluoroacetic acid. Pyridine-induced disassembly was found to be most pronounced for Pd complexes containing N-donor ligands of low basicity. At the same time, these assemblies displayed high acid resistance. The contrasting stability in the presence of acid or pyridine can be used for the pH-controlled switching between different metallosupramolecular structures.

Palladium-induced transformation of nematic liquid crystals to robust metallogel comprising self-assembled nanowires

Transformation of nematic liquid crystals to metallogels.

Discrete and Polymeric Self-Assembled Palladium(II) Complexes as Supramolecular Gelators

Supramolecular gels prepared from low-molecular-weight gelators have been extensively explored. However, the exploitation of discrete or polymeric metal complexes as gelators is a relatively recent trend. The synthesis of self-assembled coordination complexes from palladium(II) and selected ligands is well established, but the potential of these complexes as gelators is a less explored treasure. Herein we focus on the gelation abilities of some self-assembled palladium(II) complexes and the resulting unique properties. First, discrete complexes with PdL, PdL₂ , Pd₂ L, Pd₂ L₂ , Pd₂ L₄ , and Pd₃ L₆ compositions are discussed. Second, gelation behavior promoted by coordination-polymer-like gelators formed in situ is explored. These gel samples have been employed in catalysis and the uptake of organic and dye molecules from the solution and gas phases. It is concluded that untapped unique properties can be realized by further exploration of designer palladium(II) complexes.

Ligand Isomerism in Coordination Cages

Complexation reactions of palladium(II) nitrate with a set of 3-pyridyl appended nonchelating bidentate ligands possessing regioisomeric phenylene-diurea functionalities as spacers were carried out. The ligands utilized in this study are 1,1'-(1,2-phenylene)bis(3-(pyridin-3-yl)urea), L1; 1,1'-(1,3-phenylene)bis(3-(pyridin-3-yl)urea), L2; and 1,1'-(1,4-phenylene)bis(3-(pyridin-3-yl)urea), L3. The complexation reactions of the ligands (L1, L2, and L3) with palladium(II) produced single discrete isomeric cages (1, 2, and 3) of Pd₂L₄ formulation in each case and thereby illustrated ligand-isomerism in coordination cages. All 16 hydrogen atoms of eight urea moieties present in four ligand strands are delineated completely endohedrally in cage 1 and completely exohedrally in cage 3, whereas cage 2 exhibited half of the urea hydrogens in exohedral locations and the remaining half in endohedral locations. In addition to the variable number of solvent molecules, the cavities of cages 1 and 2 lodged four and two nitrate ions, respectively, using the endohedral (H)_urea atoms (i.e., NH groups) as binding sites, whereas the cavity of 3 remained anion free. The abilities of the complexes 1-3 for adsorption of CO₂ gas are demonstrated, and their behaviors are compared.

Uranyl dication mediated photoswitching of a calix[4]pyrrole-based metal coordination cage

A set of self-assembled tri- and tetrapodal metal coordination cage structures (cage-1 and cage-2, respectively) constructed from the uranyl dication (UO22+) and a dibenzoic acid functionalised cis-calix[4]pyrrole (1) are described. The inherent photochemical reactivity of the uranyl dication mediates the transformation of cage-1 to cage-2via the activation of molecular oxygen.