Urea and thiourea based coordination polymers and metal-organic frameworks: Synthesis, structure and applications

Thiophene-Functionalized Cadmium(II)-Based Metal-Organic Frameworks for CO2 Adsorption with Gate-Opening Effect, Separation, and Catalytic Conversion

Two new porous three-dimensional cadmium(II) metal-organic frameworks (MOFs) containing thiophene-appended carboxylate acid ligands, formulated as [Cd(L1)(4,4'-Bipy)]n.2n(DMF) (1) and [Cd(L2)(4,4'-Bipy)]n.2n(DMF) (2) [where L1 = 5-{(thiophen-2-ylmethyl)amino}isophthalate, L2 = 5-{(thiophen-3-ylmethyl)amino}isophthalate, 4,4'-Bipy = 4,4'-bipyridine, and DMF = N,N'-dimethylformamide] have been synthesized and structurally characterized. The gas adsorption analysis of the activated MOFs shows that they specifically capture CO2 (uptake amount 4.36 mmol/g under 1 bar at 195 K) over N2 and CH4. Moreover, both MOFs show a gate-opening-closing phenomenon, which features the S-shaped isotherms with impressive hysteretic desorption during the CO2 adsorption-desorption process at 195 K. Ideal adsorbed solution theory (IAST) calculations of these MOFs displayed that the obtained selectivity values for CO2/CH4 (50:50) and CO2/N2 (15:85) are approximately 8.6-23 and 93-565, respectively. Configurational bias Monte Carlo simulation was performed to understand the mechanism behind the better CO2 adsorption by these MOFs. Catalytic activity of the MOFs for the CO2 fixation reactions with different epoxides to form cyclic carbonates were tested. These MOFs demonstrated a significantly high conversion (94-99%) of epichlorohydrin to the corresponding cyclic carbonate within 8 h of reaction time at 1 bar of CO2 pressure, at 70 °C, and they can be reused up to five cycles without losing considerably their activity.

Advancements in mercury detection using surface-enhanced Raman spectroscopy (SERS) and ion-imprinted polymers (IIPs): a review

Mercury (Hg) contamination remains a major environmental concern primarily due to its presence at trace levels, making monitoring the concentration of Hg challenging. Sensitivity and selectivity are significant challenges in the development of mercury sensors. Surface-enhanced Raman spectroscopy (SERS) and ion-imprinted polymers (IIPs) are two distinct analytical methods developed and employed for mercury detection. In this review, we provide an overview of the key aspects of SERS and IIP methodologies, focusing on the recent advances in sensitivity and selectivity for mercury detection. By examining the critical parameters and challenges commonly encountered in this area of research, as reported in the literature, we present a set of recommendations. These recommendations cover solid and colloidal SERS substrates, appropriate Raman reporter/probe molecules, and customization of IIPs for mercury sensing and removal. Furthermore, we provide a perspective on the potential integration of SERS with IIPs to achieve enhanced sensitivity and selectivity in mercury detection. Our aim is to foster the establishment of a SERS-IIP hybrid method as a robust analytical tool for mercury detection across diverse fields.

Yellow-Orange Emission in Sb3+-Doped Hexakis(thiocarbamidium) Hexabromoindium(III) Tribromide

A luminescent zero-dimensional organic-inorganic hybrid indium halide (TUH)6[In1-xSbxBr6]Br3 (TU = thiourea, 0 ≤ x ≤ 0.0998) was synthesized via the solvothermal method. In structures, resolved by single-crystal X-ray diffraction, isolated distorted [InBr6]3- and [SbBr6]3- octahedra are linked to organic TUH+ cations by intermolecular N-H···Br and N-H···S hydrogen bonds. The crystals were characterized by elemental analysis, TG-DSC, powder X-ray diffraction, FTIR analysis, and steady-state absorption and photoluminescence spectroscopy. (TUH)6[In1-xSbxBr6]Br3 exhibits a broadband yellow-orange emission centered at 595-602 nm with a half-width of 141-149 nm (0.48-0.52 eV) and a large Stokes shift of 232-238 nm (1.33-1.35 eV). This emission can be attributed to the self-trapped exciton emission of triplet states of the octahedral anion [SbBr6]3- or [InBr6]3-. Two possible emission mechanisms were discussed. Doping with Sb3+ leads to a significant increase in photoluminescence quantum yield from 25.7 at x = 0 to 48.4% at x = 0.0065, when excited at 365 nm, indicating the potential use of (TUH)6[In1-xSbxBr6]Br3 compounds in the field of photonics.

The post-synthesis modification (PSM) of MOFs for catalysis

While there are myriad ways to construct metal-organic framework (MOF) based catalysts, the introduction of catalytic functionality via covalent post-synthesis functionalization (PSM) offers multiple advantages: (i) a wide range of different catalyst types are generated from a handful of well-known parent MOFs, (ii) MOF catalyst properties can be systematically tuned while changing few variables, and (iii) catalytically active functional groups that would otherwise interfere with MOF assembly can be introduced facilely. This last advantage is particularly crucial for our quest to generate MOF active sites that are decorated with multiple functional groups capable of cooperative activity, analogous to enzyme active sites.

Halogen-Decorated Metal-Organic Frameworks for Efficient and Selective CO2 Capture, Separation, and Chemical Fixation with Epoxides under Mild Conditions

In the present work, three novel halogen-appended cadmium(II) metal-organic frameworks [Cd2(L1)2(4,4'-Bipy)2]n·4n(DMF) (1), [Cd2(L2)2(4,4'-Bipy)2]n·3n(DMF) (2), and [Cd(L3)(4,4'-Bipy)]n·2n(DMF) (3) [where L1 = 5-{(4-bromobenzyl)amino}isophthalate; L2 = 5-{(4-chlorobenzyl)amino}isophthalate; L3 = 5-{(4-fluorobenzyl)amino}isophthalate; 4,4'-Bipy = 4,4'-bipyridine; and DMF = N,N'-dimethylformamide] have been synthesized under solvothermal conditions and characterized by various analytical techniques. The single-crystal X-ray diffraction analysis demonstrated that all the MOFs feature a similar type of three-dimensional structure having a binuclear [Cd2(COO)4(N)4] secondary building block unit. Moreover, MOFs 1 and 2 contain one-dimensional channels along the b-axis, whereas MOF 3 possesses a 1D channel along the a-axis. In these MOFs, the pores are decorated with multifunctional groups, i.e., halogen and amine. The gas adsorption analysis of these MOFs demonstrate that they display high uptake of CO2 (up to 5.34 mmol/g) over N2 and CH4. The isosteric heat of adsorption (Qst) value for CO2 at zero loadings is in the range of 18-26 kJ mol-1. In order to understand the mechanism behind the better adsorption of CO2 by our MOFs, we have also performed configurational bias Monte Carlo simulation studies, which confirm that the interaction between our MOFs and CO2 is stronger compared to those with N2 and CH4. Various noncovalent interactions, e.g., halogen (X)···O, Cd···O, and O···O, between CO2 and the halogen atom, the Cd(II) metal center, and the carboxylate group from the MOFs are observed, respectively, which may be a reason for the higher carbon dioxide adsorption. Ideal adsorbed solution theory (IAST) calculations of MOF 1 demonstrate that the obtained selectivity values for CO2/CH4 (50:50) and CO2/N2 (15:85) are ca. 28 and 193 at 273 K, respectively. However, upon increasing the temperature to 298 K, the selectivity value (S = 34) decreases significantly for the CO2/N2 mixture. We have also calculated the breakthrough analysis curves for all the MOFs using mixtures of CO2/CH4 (50:50) and CO2/N2 (50:50 and 15:85) at different entering gas velocities and observed larger retention times for CO2 in comparison with other gases, which also signifies the stronger interaction between our MOFs and CO2. Moreover, due to the presence of Lewis acidic metal centers, these MOFs act as heterogeneous catalysts for the CO2 fixation reactions with different epoxides in the presence of tetrabutyl ammonium bromide (TBAB), for conversion into industrially valuable cyclic carbonates. These MOFs exhibit a high conversion (96-99%) of epichlorohydrin (ECH) to the corresponding cyclic carbonate 4-(chloromethyl)-1,3-dioxolan-2-one after 12 h of reaction time at 1 bar of CO2 pressure, at 65 °C. The MOFs can be reused up to four cycles without compromising their structural integrity as well as without losing their activity significantly.

Comparative study between three carbonaceous nanoblades and nanodarts for antimicrobial applications

The design of nanostructured materials occupies a privileged position in the development and management of affordable and effective technology in the antibacterial sector. Here, we discuss the antimicrobial properties of three carbonaceous nanoblades and nanodarts materials of graphene oxide (GO), reduced graphene oxide (RGO), and single-wall carbon nanotubes (SWCNTs) that have a mechano-bactericidal effect, and the ability to piercing or slicing bacterial membranes. To demonstrate the significance of size, morphology and composition on the antibacterial activity mechanism, the designed nanomaterials have been characterized. The minimum inhibitory concentration (MIC), standard agar well diffusion, and transmission electron microscopy were utilized to evaluate the antibacterial activity of GO, RGO, and SWCNTs. Based on the evidence obtained, the three carbonaceous materials exhibit activity against all microbial strains tested by completely encapsulating bacterial cells and causing morphological disruption by degrading the microbial cell membrane in the order of RGO > GO > SWCNTs. Because of the external cell wall structure and outer membrane proteins, the synthesized carbonaceous nanomaterials exhibited higher antibacterial activity against Gram-positive bacterial strains than Gram-negative and fungal microorganisms. RGO had the lowest MIC values (0.062, 0.125, and 0.25 mg/mL against B. subtilis, S. aureus, and E. coli, respectively), as well as minimum fungal concentrations (0.5 mg/mL for both A. fumigatus and C. albicans). At 12 hr, the cell viability values against tested microbial strains were completely suppressed. Cell lysis and death occurred as a result of severe membrane damage caused by microorganisms perched on RGO nanoblades. Our work gives an insight into the design of effective graphene-based antimicrobial materials for water treatment and remediation.

Polyaromatic Group Embedded Cd(II)-Coordination Polymers for Microwave-Assisted Solvent-Free Strecker-Type Cyanation of Acetals

In this work, two new 1D Cd(II) coordination polymers (CPs), [Cd(L1)(NMF)₂]_n (1) and [Cd(L2)(DMF)(H₂O)₂]_n·n(H₂O) (2), have been synthesized, characterized and employed as catalysts for the microwave-assisted solvent-free Strecker-type cyanation of different acetals. Solvothermal reaction between the pro-ligand, 5-{(pyren-1-ylmethyl)amino}isophthalic acid (H₂L1) or 5-{(anthracen-9-ylmethyl)amino}isophthalic acid (H₂L2), and Cd(NO₃)₂.6H₂O in the presence of NMF or DMF:THF solvent, produces the coordination polymer 1 or 2, respectively. These frameworks were characterized by single-crystal and powder X-ray diffraction analyses, ATR-FTIR, elemental and thermogravimetry analysis. Their structural analysis revealed that both CPs show one-dimensional structures, but CP 1 has a 1D double chain type structure whereas CP 2 is a simple one-dimensional network. In CP 1, the dinuclear {Cd₂(COO)₄} unit acts as a secondary building unit (SBU) and the assembly of dinuclear SBUs with deprotonated ligand (L1^2-) led to the formation of a 1D double chain framework. In contrast, no SBU was observed in CP 2. To test the catalytic effectiveness of these 1D compounds, the solvent-free Strecker-type cyanation reactions of different acetals in presence of trimethylsilyl cyanide (TMSCN) was studied with CPs 1 and 2 as heterogenous catalysts. CP 1 displays a higher activity (yield 95%) compared to CP 2 (yield 84%) after the same reaction time. This is accounted for by the strong hydrogen bonding packing network in CP 2 that hampers the accessibility of the metal centers, and the presence of the dinuclear Cd(II) SBU in CP 1 which can promote the catalytic process in comparison with the mononuclear Cd(II) center in CP 2. Moreover, the recyclability and heterogeneity of both CPs were tested, demonstrating that they can be recyclable for at least for four cycles without losing their structural integrity and catalytic activity.

Assembled Morphology of Copper-Thiourea Coordination-Mediated Metallo-Supramolecular Polymers

Metallo-supramolecular polymers represent a powerful platform to construct self-assembled morphologies. Copper-thiourea (Cu-TU) coordination interactions, though have been extensively studied in small molecular system, the role of TU motifs in synthetic polymers using metal-ligand coordination to afford supramolecular aggregation and their morphology are often overlooked. Herein, an amphiphilic random copolymer, poly(oligo(ethylene glycol) ethyl acrylate-r-acylthiourea) (P(OEGEA-r-ATU)), bearing pendant TU motifs behaving as the ligand to coordinate Cu, a design characterized by core-coordinated metallo-supramolecular polymer is rationally synthesized. Indeed, rod-like nano-objects are successfully generated via the self-assembly and coordination interaction between P(OEGEA-r-ATU) and Cu. The spatial distribution of TU moieties in polymer chain, along with their Cu chelating capability, featuring the interchain coordination interaction, is tightly related to metallo-supramolecular polymer organization. The specific Cu-TU coordination interactions enable the prompted robustness and stability of soft P(OEGEA-r-ATU), induce the polymer chain configuration, which eventually furnish efficient fabrication of rod-like nano-objects via straightforward nanoprecipitation procedure. These structural motifs of copper-coordinated, rod-like nano-objects from such metallo-supramolecular polymers endow the potential therapeutic properties, such as anti-inflammatory and antitumor effects.

Unravelling Structural Dynamics, Supramolecular Behavior, and Chiroptical Properties of Enantiomerically Pure Macrocyclic Tertiary Ureas and Thioureas

The introduction of urea or thiourea functionality to the macrocycle skeleton represents an alternative way to control conformational dynamics of chiral, polyamines of a figure-shaped periodical structure. Formally highly symmetrical, these macrocycles may adapt diverse conformations, depending on the nature of an amide linker and on a substitution pattern within the aromatic units. The type of heteroatom X in the N-C(═X)-N units present in each vertex of the macrocycle core constitutes the main factor determining the chiroptical properties. In contrast to the urea-containing derivatives, the electronic circular dichroism of thioureas is controlled by the chiral neighborhood closest to the chromophore. The dynamically induced exciton couplet is observed when the biphenyl chromophores are present in the macrocycle core. In the solid state, the seemingly disordered molecules may create ordered networks stabilized by intermolecular S···halogen, H···halogen, and S···H interactions. The presence of two bromine substituents in each aromatic unit in thiourea-derived trianglamine gives rise to a self-sorting phenomenon in the crystal. In solution, this particular macrocycle exists as a dynamic equimolar mixture of two conformational diastereoisomers, differing in the spatial (clockwise and counter clockwise) arrangement of the C-Br bonds. In the crystal lattice, macrocycles of a given handedness assemble into homohelical layers.

A Heniconuclear {Mn21} Cluster-Based Coordination Polymer with Manganese(II) Linkers Showing High Proton Conductivity

An unprecedented metal-linked cluster-based coordination polymer, composed of heniconuclear {Mn₂₁} clusters and Mn(II) ions as the nodes and linkers, respectively, was self-assembled from a facile aqueous synthesis. The structural analysis reveals that the compound possesses a rare 3D 8-connected hex framework topology. Significantly, the compound demonstrates a high proton conductivity of 1.06 mS cm^-1 at 373 K and 98% RH and exhibits a magnetocaloric effect with a magnetic entropy change of -9.94 J kg^-1 K^-1 at H = 80 kOe and T = 6.0 K.

Polyaromatic Carboxylate Ligands Based Zn(II) Coordination Polymers for Ultrasound-Assisted One-Pot Tandem Deacetalization–Knoevenagel Reactions

Solvothermal reactions between the polyaromatic group containing carboxylic acid pro-ligands 5-{(pyren-1-ylmethyl)amino}isophthalic acid (H2L1) and 5-{(anthracen-9-ylmethyl)amino}isophthalic acid (H2L2) with Zn(NO3)2·6H2O led to the formation of the new 1D coordination polymer [Zn(L1)(NMF)]n (1) and four other coordination polymers, [Zn(L1)(DMF)]n (2), [Zn(L1)(4,4′-Bipy)]n (3), [Zn(L2)(DMF)(H2O)2]n·n(H2O) (4) and [Zn2(L2)2(DMF)(CH3OH)]n (5), which were previously reported by our group. Single crystal X-ray diffraction analyses revealed that the CP 1 has a one-dimensional (1D) double-chain-type structure similar to that of CP 2. For CP 3, the assembly of the Zn(II) ion with a deprotonated L12− ligand and 4,4′-bipyridine produces a 3D network. CP 4 and 5 exhibit 1D linear and 2D layered-type structures. The ultrasound-assisted tandem reactions promoted by CPs have not yet been well studied. Thus, in the present work, we have investigated the catalytic activities of the newly synthesized CP 1, as well as of the other CPs 2–5, towards the tandem deacetalization–Knoevenagel condensation reactions of various acetals under ultrasonic irradiation. They proved to be highly efficient, with special emphasis on catalyst 1, which completely converted the substrate (benzaldehyde dimethyl acetal) into the desired product (2-benzylidenemalononitrile) after 2 h. The stability of the catalysts, namely regarding the action of ultrasonic radiation, was demonstrated by their reuse, where only a slight loss of activity was observed after four cycles. Heterogeneity was also demonstrated, and no leaching was detected over the various cycles.