Molecular Co-Catalyst Confined within a Metallacage for Enhanced Photocatalytic CO2 Reduction.

The construction of structurally well-defined supramolecular hosts to accommodate catalytically active species within a cavity is a promising way to address catalyst deactivation. The resulting supramolecular catalysts can significantly improve the utilization of catalytic sites, thereby achieving a highly efficient chemical conversion. In this study, the Co-metalated phthalocyanine (Pc-Co) was successfully confined within a tetragonal prismatic metallacage, leading to the formation of a distinctive type of supramolecular photocatalyst (Pc-Co@Cage). The host-guest architecture of Pc-Co@Cage was unambiguously elucidated by single-crystal X-ray diffraction (SCXRD), NMR, and ESI-TOF-MS, revealing that the single cobalt active site can be thoroughly isolated within the space-restricted microenvironment. In addition, we found that Pc-Co@Cage can serve as a homogeneous supramolecular photocatalyst that displays high CO2 to CO conversion in aqueous media under visible light irradiation. This supramolecular photocatalyst exhibits an obvious improvement in activity (TONCO = 4175) and selectivity (SelCO = 92%) relative to the nonconfined Pc-Co catalyst (TONCO = 500, SelCO = 54%). The present strategy provided a rare example for the construction of a highly active, selective, and stable photocatalyst for CO2 reduction through a cavity-confined molecular catalyst within a discrete metallacage.

Selective Construction and Structural Transformation of Homogeneous Linear Metalla[4]catenane and Metalla[2]catenane Assemblies.

Although the synthesis of mechanically interlocked molecules has been extensively researched, selectively constructing homogeneous linear [4]catenanes remains a formidable challenge. Here, we selectively constructed a homogeneous linear metalla[4]catenane in a one-step process through the coordination-driven self-assembly of a bidentate benzothiadiazole derivative ligand and a binuclear half-sandwich rhodium precursor. The formation of metalla[4]catenanes was facilitated by cooperative interactions between strong sandwich-type π-π stacking and non-classical hydrogen bonds between the components. Moreover, by modulating the aromatic substituents on the binuclear precursor, two homogeneous metalla[2]catenanes were obtained. The molecular structures of these metallacatenanes were unambiguously characterized by single-crystal X-ray diffraction analysis. Additionally, reversible structural transformation between metal-catenanes and the corresponding metallarectangles could be achieved by altering their concentration, as confirmed by mass spectrometry and NMR spectroscopy studies.

Trefoil-Shaped Metal-Organic Cages as Fluorescent Chemosensors for Multiple Detection of Fe3+, Cr2O72-, and Antibiotics.

The construction of metal-organic cages (MOCs) with specific structures and fluorescence sensing properties is of much importance and challenging. Herein, a novel phenanthroline-based metal-organic cage, [Cd3L3·6MeOH·6H2O] (1), was synthesized by metal-directed assembly of the ligand 3,3'-[(1E,1'E)-(1,10-phenanthroline-2,9-diyl)bis(ethene-2,1-diyl)]dibenzoic acid (H2L) and CdI2 using a solvothermal method. According to single-crystal X-ray analysis, cage 1 exhibits a rare trefoil-shaped structure. Meanwhile, the discrete MOCs are further stacked into a 3D porous supramolecular structure through abundant intermolecular C-H···O interactions. Additionally, through exploration of fluorescence sensing on cations, anions, and antibiotics in aqueous solution, the experimental results indicate that cage 1 has excellent fluorescence sensing abilities for Fe3+, Cr2O72-, and nitrofuran and nitroimidazole antibiotics. The sensing ability of 1 remains unaltered for five cycles toward all analytes. The above results suggested that cage 1 can be considered a potential multiple sensor for the detection of Fe3+, Cr2O72-, and some antibiotics.

Formation of Metallosupramolecular Helicates and Mesocates from Poly-N-Heterocyclic Carbene Ligands.

In this work, a series of poly-NHC-based tetranuclear silver helicates and mesocates were synthesized from the silver-mediated self-assembly of the ligands involving multiple tridentate CNC-type pincer units and NHC coordination sites. The silver helicate was found to be transferred to a gold mesocate upon metal exchange reaction. The metallosupramolecular helicates and mesocates have been fully characterized by single-crystal X-ray crystallography, mass spectrometry, and multinuclear nuclear magnetic resonance spectroscopies. This study provides an example of the selective preparation of poly-NHC-based helicates or mesocates depending on the size of metal ions and the steric effect of ligands.

A novel 8-hydroxyquinoline derivative induces breast cancer cell death through paraptosis and apoptosis.

Chemotherapy represents one of the main conventional therapies for breast cancer. However, tumor cells develop mechanisms to evade chemotherapeutic-induced apoptosis. Thus, it is of great significance to induce non-apoptotic cell death modes, such as paraptosis, in breast cancer. Herein, a novel 8-hydroxyquinoline derivative, 5,7-dibromo-8-(methoxymethoxy)-2-methylquinoline (HQ-11), was obtained and its potential anti-breast cancer mechanisms were investigated. Our results showed that extensive cytoplasmic vacuoles derived from the endoplasmic reticulum (ER) and mitochondria were appeared in MCF7 and MDA-MB-231 breast cancer cells by HQ-11 incubation, and pretreatment of cycloheximide was able to inhibit this vacuolation and HQ-11-induced cell death, showing the characteristics of paraptosis. ER stress was involved in HQ-11-caused paraptosis evidenced by the increase of glucose-regulated protein 78, C/EBP homologous protein and polyubiquitinated proteins. Molecular docking analysis revealed a favorable binding mode of HQ-11 in the active site of the chymotrypsin-like ß5 subunit of the proteasome, indicative of proteasome dysfunction under HQ-11 treatment, which might result in further aggravated ER stress. Furthermore, treatment of HQ-11 resulted in increased phosphorylation of extracellular signal-regulated kinase (ERK) and c-Jun NH2-terminal kinase, and inhibition of ERK with U0126 significantly attenuated HQ-11-induced ER stress and paraptosis. In addition, exposure to HQ-11 also caused apoptosis in breast cancer cells partially through activation of ERK pathway. All these results conclusively indicate that HQ-11 triggers two distinct cell death modes via inhibition of proteasome and activation of ERK pathway in breast cancer cells, providing a promising candidate in future anti-breast cancer therapy.

Highly Efficient and Selective Visible-Light Driven CO2 Reduction by Two Co-Based Catalysts in Aqueous Solution.

Photocatalytic CO2 reduction has been considered as a promising approach to solve energy and environmental problems. Nevertheless, developing inexpensive photocatalysts with high efficiency and selectivity remains a big challenge. In this study, two Co-based complexes [Co2(L1)Cl2] (1-Co) and [Co(L2)Cl] (2-Co) were synthesized by treating two DPA-based (DPA: dipicolylamine) ligands with Co2+, respectively. Under visible-light irradiation, the performance of 1-Co as a homogeneous photocatalyst for CO2 reduction in aqueous media has been explored by using [Ru(phen)3]2+ as a photosensitizer, and triethylolamine (TEOA) as a sacrificial reductant. 1-Co shows high photocatalytic activity for CO2-to-CO conversion, corresponding to the high TONCO of 2600 and TOFCO of 260 h-1 (TONCO = turnover number for CO; TOFCO = turnover frequency for CO). High selectivity of 97% for CO formation is also achieved. The control experiments catalyzed by 2-Co demonstrated that two Co(II) centers in 1-Co may operate independently and activate one CO2 molecule each. Furthermore, the proposed mechanism of 1-Co for photocatalytic CO2 reduction has been investigated via electrochemical analysis, a series of quenching experiments, and density functional theory calculations.

8-Hydroxyquinolinate-Based Metal-Organic Frameworks: Synthesis, Tunable Luminescent Properties, and Highly Sensitive Detection of Small Molecules and Metal Ions.

Five new metal-organic frameworks, [Zn2L2]·2DMF·2MeOH (1), [Zn2L2(py)2] (2), [Cd2L2]·Diox·MeOH·6H2O (3), [Mn2L2]·2DMF·2MeOH (4), and [Co2L2]·2DMF·4H2O (5), were assembled by using a novel 8-hydroxyquinolinate derivative H2L with different metal ions. Complex 1 features a 3D porous network consisting of meso-helical chains ( P + M) built from metal-ligand coordination bonds. The adjacent dinuclear ZnII building blocks in 2 are connected together to generate a 2D grid network. In complex 3, each binuclear motif is bound to four ZnII ions to produce a 2D layer structure that stacks into a 3D porous structure. The framework of complex 4 is isostructural to 5, featuring a 21 helical chain built from [M2L2] units (M = Mn or Co). The adjacent meso-helices associated in parallel are interconnected by the phenolate µ2-O atoms of H2L to give rise to a 2D network. Distinct solid-state luminescence properties of 1-3 were observed, arising from their different metal nodes and frameworks. In particular, complex 1 exhibited excellent stability in both common organic solvents and H2O, thus facilitating its utility as a chemical sensor. Remarkably, luminescent 1 showed highly sensitive detection for nitroaromatic molecules in methanol and Fe3+ ion in H2O even in the presence of other interfering metal cations.

Chiral Cu(salen)-Based Metal-Organic Framework for Heterogeneously Catalyzed Aziridination and Amination of Olefins.

A homochiral 3D porous metal-organic framework was assembled from a chiral dicarboxylic acid-functionalized Cu(salen)-based catalyst and could serve as an efficient heterogeneous catalyst for aziridination and allylic amination of olefins. Besides easy separation and reuse of the catalyst, the chiral framework confinement could impart substrate size selectivity, enhance catalyst activity, and induce product enantioselectivity.

Chiral nanoporous metal-metallosalen frameworks for hydrolytic kinetic resolution of epoxides.

Chiral nanoporous metal-organic frameworks are constructed by using dicarboxyl-functionalized chiral Ni(salen) and Co(salen) ligands. The Co(salen)-based framework is shown to be an efficient and recyclable heterogeneous catalyst for hydrolytic kinetic resolution (HKR) of racemic epoxides with up to 99.5% ee. The MOF structure brings Co(salen) units into a highly dense arrangement and close proximity that enhances bimetallic cooperative interactions, leading to improved catalytic activity and enantioselectivity in HKR compared with its homogeneous analogues, especially at low catalyst/substrate ratios.

Highly efficient and selective photocatalytic CO2 to CO conversion in aqueous solution.

Five molecular complexes with different non-noble metal centers were synthesized. The Co-based complex displays the highest photocatalytic performance for CO2 to CO conversion in aqueous media. It achieves high activity (TON = 41 017 and TOF = 3.80 s-1) and selectivity (87%) for the production of CO.

Anion-driven conformational polymorphism in homochiral helical coordination polymers.

Three homochiral 3D frameworks are assembled based on periodically ordered arrays of helices built from axial chiral 3,3'-bipyridine-5,5',6,6'-tetramethyl-2,2'-dimethoxy-1,1'-biphenyl ligands and linearly coordinated Ag(I) ions. The aggregation behavior of silver salts and the ditopic ligand in solutions was investigated by a variety of techniques, including (1)H NMR, UV-vis, CD, GPC and MALDI-TOF. The cationic polymer skeleton exhibits an unprecedented conformational polymorphism in the solid-state, folding into two-, three- and four-fold helices with NO(3)(-), PF(6)(-) and ClO(4)(-) as the counteranion, respectively. The two-fold helices cross-link via argentophilic Ag-Ag interactions to form sextuple helices, which lead to a three-dimensional (3D) chiral framework. The three-fold or four-fold helices, on the other hand, self-associates in pairs to form three-dimensional tubular architectures. This anion-dependent self-assembly behavior can be rationalized by considering the sizes, geometries and binding abilities of the counteranions and subsequent chain conformation to minimize steric repulsions and maximize secondary interactions.

Enantioselective recognition and separation by a homochiral porous lamellar solid based on unsymmetrical Schiff base metal complexes.

Our Schiff has come in: A homochiral porous lamellar solid based on chiral unsymmetrical Schiff base metal complexes was assembled by using coordination and hydrogen bonds (see picture). The host features a flexible helical framework and chiral amphiphilic channel surfaces capable of multiple interactions with guest species.A homochiral lamellar supramolecular host system has been developed by treating 3-[(E)-{[(1R,2R)-2-aminocyclohexyl]imino}methyl]-4-hydroxybenzoic acid (H(2)L) with copper nitrate and characterized by a variety of techniques including microanalysis, IR spectroscopy, thermogravimetric analysis (TGA), circular dichroism (CD) spectroscopy, and powder and single-crystal X-ray diffraction. Tridentate Schiff base L ligands link adjacent metal centers to form 1D coordination polymeric chains using tridentate N(2)O donors and carboxylate groups, while interchain metal-oxygen and hydrogen-bonding interactions further link 1D polymeric chains to a porous lamellar solid. The host features a flexible helical framework for guest inclusions and chiral amphiphilic channel surfaces lined with amine hydrogen atoms and aliphatic groups capable of multiple interactions with guest species. It allows for the development of an efficient approach for highly enantioselective separation of racemic secondary alcohols by inclusion crystallization followed by distillation (>99.5 % ee). In addition, the host including different alcohols exhibits guest-responsive ferroelectric behavior.

Five 8-hydroxyquinolinate-based coordination polymers with tunable structures and photoluminescent properties for sensing nitroaromatics.

Using two 8-hydroxyquinolinate ligands (L1-MOM and L2-MOM) containing 3-pyridyl or 4-pyridyl groups, five novel coordination polymers, namely, [Zn3(L1)6] (1), [Zn(L1)2]·2MeOH (2), [Zn(L2)2] (3), [Cd(L2)2] (4), and [Cd4(L1)6]·13H2O (5), were synthesized and characterized by a variety of techniques. Single-crystal X-ray structures have revealed that these coordination polymers exhibit a structural diversification due to the different choices of metal salts and the effect of pyridyl nitrogen position. Compounds 1-5 exhibited different fluorescence emissions and lifetimes upon excitation in the solid state. The sensing behavior of these polymers was also investigated upon exposure to vapors of various nitroaromatic molecules (analytes). The results show that all five polymers are capable of sensing these nitroaromatic molecules in the vapor phase through fluorescence quenching. Interestingly, 3 exhibits superior sensitivity to the analytes in comparison with other polymers. 2-Nitrotoluene quenches the emission of 3 by as much as 96%.

Six Zn(II) and Cd(II) coordination polymers assembled from a similar binuclear building unit: tunable structures and luminescence properties.

Six Zn(ii) and Cd(ii) coordination polymers were constructed by treating a 2-substituted 8-hydroxyquinolinate ligand containing a pyridyl group with zinc or cadmium salts, and characterized by a variety of techniques. Interestingly, based on a similar binuclear Zn(ii) or Cd(ii) building unit, the supramolecular structures of the six coordination polymers () exhibit an unprecedented structural diversification due to the different choices of metal salts. and represent a novel 2D framework containing 1D infinite right- and left-handed helical chains. and are 2D coordination frameworks based on binuclear Cd(ii) building units. For and , the L ligands can bridge binuclear building units forming a 1D infinite chain. Interestingly, the adjacent Cd2O2 planes of the 1D chain in are in parallel with each other, while the dihedral angle between the two Zn2O2 planes in is 83.43°. Photoluminescence properties revealed that the six coordination polymers exhibit redshifted emission maximum compared with the free ligand HL, which can be ascribed to an increased conformational rigidity and the fabrication of coplanar binuclear building units M2L2 in . Coordination polymers also display distinct fluorescence lifetimes and quantum yields because of their different metal centers and supramolecular structures.

Anion-directed self-assembly of two half-sandwich ruthenium-based metallamacrocycles as catalysts for water oxidation.

The binuclear [η(6) -(cymene)Ru(L)]2 (OTf)2 (TfO(-) =trifluoromethanesulfonate) and tetranuclear [η(6) -(cymene)Ru(L)]4 (NO3 )4 metallacycles were prepared by treating the pyridyl-substituted 8-hydroxyquinoline ligand (E)-2-[2-(pyridin-3-yl)vinyl]quinolin-8-ol (HL) with [(p-cymene)Ru(µ-Cl)Cl]2 in the presence of AgOTf or AgNO3 . The molecular structures of these complexes were confirmed by single-crystal X-ray diffraction, which revealed that both complexes have macrocycle frameworks induced by the TfO(-) and NO3 (-) counteranions, respectively. The electrochemical properties of the two metallacycles were investigated by cyclic voltammetry, which showed that they have great potential as catalysts for water oxidation. Good efficiency was obtained by utilizing the nitrate complex as a water oxidation catalyst in the presence of a Ce(IV) salt as an oxidant at high pH values.

Structural and luminescence modulation in 8-hydroxyquinolinate-based coordination polymers by varying the dicarboxylic acid.

Two Zn(ii) and Cd(ii) coordination polymers [ZnL2·2DMF] (1) and [CdL(OAc)] (2) were first synthesized by treating a novel 2-substituted 8-hydroxyquinolinate ligand HL involving a pyridyl group with zinc or cadmium salts. Two dicarboxylic acid ligands (H2BDC = 1,4-benzenedicarboxylic acid; H2BPDC = 4,4'-biphenyldicarboxylic acid) are employed as secondary auxiliary ligands to perform a systematic study on the structural diversities in the M(ii)-quinolinate frameworks. By introducing two dicarboxylate anions in the reaction system, four new polymers [Zn2L2(BDC)] (3), [Zn3L2I2(BPDC)·2MeOH·8H2O] (4), [Cd2L2(BDC)] (5) and [Cd2L2(BPDC)·2MeOH·4H2O] (6) were obtained. Complex 1 possesses a two-dimensional (2D) square grid containing meso-helical chains. Complex 2 is a 2D network fabricated by binuclear {Zn2} secondary building units (SBUs). Complexes 3 and 5 show a kind of 2D structure constructed by cyclic hexamers Zn6L4, which are divided into half by the coordinated BDC. In complex 4, the BPDC ligands bridge the 1D M(ii)-L chains into a 2D layered structure. Complex 6 presents an interesting 3D structure, in which the BPDC ligands link the binuclear Cd(ii) units into many meso-helical chains along the a and b axes. The diverse structures of complexes 1-6 indicate that the skeletons of dicarboxylate anions play an important role in the assembly of such different frameworks. Moreover, distinct fluorescence properties (emission wavelength and lifetime) of the complexes 1-6 were observed in the solid state.

Self-assembly of five 8-hydroxyquinolinate-based complexes: tunable core, supramolecular structure, and photoluminescence properties.

Five new Zn(II) complexes, namely [Zn(3)(L)(6)] (1), [Zn(2)(Cl)(2)(L)(2) (py)(2)] (2), [Zn(2)(Br)(2) (L)(2)(py)(2)] (3), [Zn(L)(2)(py)] (4), and [Zn(2)(OAc)(2)(L)(2)(py)(2)] (5), were prepared by the solvothermal reaction of ZnX(2) (X(-) =Cl(-), Br(-), F(-), and OAc(-)) salts with a 8-hydroxyquinolinate ligand (HL) that contained a trifluorophenyl group. All of the complexes were characterized by elemental analysis, IR spectroscopy, and powder and single-crystal X-ray crystallography. The building blocks exhibited unprecedented structural diversification and their self-assembly afforded one mononuclear, three binuclear, and one trinuclear Zn(II) structures in response to different anions and solvent systems. Complexes 1-5 featured four types of supramolecular network controlled by non-covalent interactions, such as π⋅⋅⋅π-stacking, C-H⋅⋅⋅π, hydrogen-bonding, and halogen-related interactions. Investigation of their photoluminescence properties exhibited disparate emission wavelengths, lifetimes, and quantum yields in the solid state.

Three Mn(II) coordination polymers with a bispyridyl-based quinolinate ligand: the anion-controlled tunable structural and magnetic properties.

Three new Mn(ii) coordination polymers, namely [Mn3L6·2H2O] (), [MnL2] (), and [MnL2·2H2O] (), were prepared by solvothermal reactions of Mn(ii) salts with a bispyridyl-based quinolinate ligand. All complexes were characterized by elemental analysis, IR spectra, powder and single-crystal X-ray crystallography. Single crystal X-ray studies show that these coordination polymers exhibit a structural diversification due to the different counteranions (OAc(-), Cl(-), and NO3(-)). Complex has a 2D supramolecular structure with a cyclic tetramer Mn3L6 secondary building unit. Complex possesses a rhombohedral grid network containing a type of meso-helical chain (P + M) constructed via the metal-ligand coordination interaction. Complex features a 3D non-porous structure based on the arrangement of 2D grids. Magnetic susceptibility measurements indicate that the three Mn(ii) polymers show disparate magnetic properties due to their different supramolecular structures.

Experimental and DFT studies of (E)-2-[2-(2,6-dichlorophenyl)ethenyl]-8-hydroxyquinoline: electronic and vibrational properties.

The title molecule (E)-2-[2-(2,6-dichlorophenyl)ethenyl]-8-hydroxyquinoline (DPEQ) was synthesized and characterized by FT-IR, UV-vis, NMR spectroscopy. The molecular geometry, vibrational frequencies and gauge independent atomic orbital (GIAO) 1H and 13C NMR chemical shift values of the compound in the ground state have been calculated by using the density functional theory (DFT) method. All the assignments of the theoretical frequencies were performed by potential energy distributions using VEDA 4 program. The calculated results indicate that the theoretical vibrational frequencies, 1H and 13C NMR chemical shift values show good agreement with experimental data. The electronic properties like UV-vis spectral analysis and HOMO-LUMO analysis of DPEQ have been reported and compared with experimental data. Information about the size, shape, charge density distribution and site of chemical reactivity of the molecule has been obtained by mapping electron density isosurface with molecular electrostatic potential (MEP).

Controllable supramolecular structures and luminescent properties of unique trimeric Zn(II) 8-hydroxyquinolinates tuned by functional substituents.

We reported here the self-assembly of two supramolecular structures based on similar trimeric Zn(II) units that are built from novel 2-substituted 8-hydroxyquinoline ligands and coordination Zn(II) ions. The aggregation behavior of zinc salt and ligand in solution was investigated by a variety of techniques, including (1)H NMR, UV-vis and photoluminescence (PL). In the solid state, the supramolecular structures can be controlled by the substituted groups (-NO(2) and -F) via intermolecular interaction, such as π···π stacking, C-H···O, and C-F···F-C interactions. As a result, the two trimeric Zn(II) complexes exhibit disparate photophysical properties. The present research holds great promise in the development of novel multinuclear Zn(II) materials, and may contribute to the understanding of structure-property relationships.