Selective removal of Cr2O72- in aqueous solution by nonporous pure crystals of cucurbit[6]uril.

Cucurbit[6]uril (Q[6]) could serve as a selective absorbent for the toxic anion Cr2O72-, which was demonstrated by the results of UV-vis, ICP, XPS, SEM, and EDS experiments. Single-crystal X-ray diffraction analysis revealed that capture capacity could be attributed to the outer-surface interactions of cucurbit[n]uril between Cr2O72- and the outer surface of Q[6].

A Green Environmental Protection Photocatalytic Molecular Reactor for Aerobic Oxidation of Sulfide to Sulfoxide.

The design and synthesis of metal-organic frameworks (MOFs) as photocatalytic molecular reactors for varied reactions have drawn great attention. In this work, we designed a novel photoactive perylenediimides-based (PDI) carboxylate ligand N,N'-di(3',3",5',5"-tetrakis(4-carboxyphenyl))-1,2,6,7-tetrachloroperylene-3,4,9,10-tetracarboxylic acid diimide (Cl-PDI-TA) and use it to successfully synthesize a novel Zr(IV)-based MOF 1 constructed from [Zr6 O8 (H2 O)8 ]8+ clusters bridged by Cl-PDI-TA ligands. Structural analysis revealed that Zr-MOF 1 manifests a 3D framework with (4,8)-connected csq topology and possesses triangular channels of ~17 Šand mesoporous hexagonal channels of ~26 Šalong c-axis. Moreover, the synthesized Zr-MOF 1 exhibits visible-light absorption and efficient photoinduced free radical generation property, making it a promising photocatalytic molecular reactor. When Zr-MOF 1 was used as a photocatalyst for the aerobic oxidation of sulfides under irradiation of visible light, it could afford the corresponding sulfoxides with high yield and selectivity. Experimental results demonstrated that the substrate sulfides could be fixed in the pores of 1 and directly transformed to the products sulfoxides in the solid state. Furthermore, the mechanism for the photocatalytic transformation was also investigated and the results revealed that the singlet oxygen (1 O2 ) and superoxide radical (O2 ⋅- ) generated by the energy transfer and electron transfer from the photoexcited Zr-MOF to oxidants were the main active species for the catalytic reactions. This work offers a perceptive comprehension of the mechanism in PDI-based MOFs for further study on photocatalytic reactions.

The impact of aggregation of AIE and ACQ moiety-integrating material on the excited state dynamics.

The investigation of the properties of aggregate materials is highly interesting because the process of aggregation can result in the disappearance of original properties and the emergence of new ones. Here, a novel fluorescent material (TPEIP), which synergistically combines aggregation-induced emission (AIE) and aggregation caused quenching (ACQ) moieties, was first synthesized by the cyclization reaction of 2,3-diamino-phenazine with 4-tetraphenylenthenealdehyde. We controlled the degree of aggregation of TPEIP to shed light on the impact of the aggregation on the excited state dynamics. TPEIP aggregation realized control over the Intersystem Crossing (ISC) rates and, in turn, the suppression of triplet excited states in MeOH, EtOH or via the simple addition of water to TPEIP solutions in DMSO. From global target analysis, the time scale was 966.2 ps for ISC for TPEIP in DMSO, but it was 860 ps in the case of TPEIP solutions featuring 5% water. The dynamics of TPEIP excited states undergo significant changes as the degree of aggregation increases. Notably, the lifetime of singlet excited states decreases, and there was a gradual diminishment in triplet states.

[C(NH2)2NHNO2][C(NH2)3](NO3)2: A Mixed Organic Cationic Hybrid Nitrate with an Unprecedented Nonlinear-Optical-Active Unit.

We herein report a mixed organic cationic hybrid nitrate, namely, [C(NH2)2NHNO2][C(NH2)3](NO3)2 (1). It was successfully achieved via combining three different planar groups: [(C(NH2)2NHNO2]+, C(NH2)3+, and NO3-. First-principles calculations confirm that the [(C(NH2)2NHNO2]+ group is an excellent cationic nonlinear-optical (NLO)-active unit. The title compound exhibits a moderate second-harmonic-generation (SHG) response (1.5 × KDP), a wide band gap (3.58 eV), and a suitable birefringence of 0.071 at 550 nm. Theoretical calculations indicate that the synergy effect between the [(C(NH2)2NHNO2]+ and C(NH2)3+ groups dominates the SHG process.

C(NH2)3(I3O8)(HI3O8)(H2I2O6)(HIO3)4·3H2O: An Unprecedented Asymmetric Guanidinium Polyiodate with a Strong Second-Harmonic-Generation Response and a Wide Band Gap.

Herein, we report an unprecedented asymmetric guanidinium polyiodate, namely, C(NH2)3(I3O8)(HI3O8)(H2I2O6)(HIO3)4·3H2O (1). The title compound was obtained via the hybridization of polyiodate anions and planar π-conjugated C(NH2)3+; meanwhile, its strong second-harmonic-generation (SHG) response (2.1 × KDP, where KDP = KH2PO4) and wide band gap (3.89 eV) were mainly dominated by the synergy effect of the aforementioned structural units.

Na2(C4O4)(H3BO3)(H2O)4·H3BO3: the first borate-squarate with strong SHG response obtained by superior synergy.

We herein report the first sodium borate-squarate, namely, Na2(C4O4)(H3BO3)(H2O)4·H3BO3 (1). It has been successfully synthesized via introducing the planar π-conjugated (C4O4)2- into a borate system. Compound 1 exhibits a strong second-harmonic-generation (SHG) response (2.1 × KDP), wide transparency in the ultraviolet (UV) region and a suitable birefringence of 0.26 at 1064 nm. Theoretical calculations indicate that the synergy effect between inorganic planar π-conjugated species H3BO3 and organic moiety (C4O4)2- dominates the SHG process.

KC9H5O6(H2O): A Promising UV Nonlinear-Optical Material with Large Birefringence Based on a π-Conjugated (C9H5O6)- Group.

In order to meet the growing needs for the laser technology and optics industries, the goal is to find suitable fundamental building blocks with large nonlinear-optical (NLO) coefficients and birefringence for an excellent-performance NLO or birefringent system. Via preliminary investigations and calculations, it has been found that the planar π-conjugated group (C9H5O6)- possesses large polarizability anisotropy (δ) and hyperpolarizability (ßmax), comparable to well-known groups such as (B3O6)3-, (C3N3O3)3-, etc. Herein, we report a new alkali-metal 3,5-dicarboxybenzoate, KC9H5O6(H2O) (KH2BTC), which crystallized in the acentric space group Pna21. Second-harmonic-generation (SHG) measurements of KH2BTC under 1064 nm laser radiation show that the SHG response of KH2BTC is 1.2 times that of KDP with type I phase-matching behavior. Birefringence measurements show that KH2BTC owns a large birefringence of about 0.372 at 550 nm. The band gap of KH2BTC obtained by ultraviolet (UV) diffuse-reflectance spectroscopy is 3.91 eV, indicating that KH2BTC has potential applications as UV NLO or birefringent materials. Theoretical calculation further confirmed that the impressive optical properties of KH2BTC are derived from the large polarizability anisotropy of the (C9H5O6)- anions.

Noncentrosymmetric (C3H7N6)6(H2PO4)4(HPO4)·4H2O and Centrosymmetric (C3H7N6)2SO4·2H2O: Exploration of Acentric Structure by Combining Planar and Tetrahedral Motifs via Hydrogen Bonds.

The combination of organic and inorganic nonlinear active units to obtain organic-inorganic hybrid materials has been proved to be a very effective method to obtain nonlinear optical (NLO) materials with excellent properties. Herein we reported two hybrid melamine-based compounds, namely, acentric (C3H7N6)6(H2PO4)4(HPO4)·4H2O (1) and centrosymmetric (C3H7N6)2SO4·2H2O (2), which were synthesized via facile solvent evaporation method. Compound 1 features a three-dimensional (3D) network structure composed of ∞[(H2PO4)4(HPO4)(H2O)4]6- layers which are further linked with ∞[(C3H7N6)6]6+ layers via hydrogen bonds. Compound 2 displays a 3D structure composed of [(C3H7N6)2(SO4)(H2O)2]∞ layers further linked with each other by hydrogen bonds. Compound 1 presents a second harmonic generation signal of about 0.1 × KDP. Furthermore, UV-vis and infrared spectra, thermal analyses, and theoretical calculation were also adopted to evaluate its NLO performance. The theoretical calculations showed that the SHG response and large birefringence of 1 were primarily caused by the (C3H7N6)+, (H2PO4)-, and (HPO4)2- groups.

Sensing Properties of NH2-MIL-101 Series for Specific Amino Acids via Turn-On Fluorescence.

Metal-organic frameworks (MOFs) have been demonstrated to be desired candidates for sensing definite species owing to their tunable composition, framework structure and functionality. In this work, the NH2-MIL-101 series was utilized for sensing specific amino acids. The results show that cysteine (Cys) can significantly enhance the fluorescence emission of NH2-MIL-101-Fe suspended in water, while NH2-MIL-101-Al exhibits the ability to sense lysine (Lys), arginine (Arg) and histidine (His) in aqueous media via turn-on fluorescence emission. Titration experiments ensure that NH2-MIL-101-Fe and NH2-MIL-101-Al can selectively and quantitatively detect these amino acids. The sensing mechanism was examined and discussed. The results of this study show that the metal centers in MOFs are crucial for sensing specific amino acids.

Cobalt-Based Metal-Organic Frameworks for Adsorption of CO2 and C2 Hydrocarbons: Effect of Auxiliary Ligands with Different Functional Groups.

Recently, metal-organic frameworks (MOFs) have been investigated as potential materials for CO2 capture and light hydrocarbon storage/separation due to their high porosity, large surface area, and tunable skeleton structures. In this work, the six cobalt-based MOFs 1-6 were successfully synthesized under solvothermal conditions by a mixed-ligand strategy. 1 and 2 have the same framework structure with a topology of {42·5}2{44·510·67·76·8}, while the structures of the 3-6 frameworks are the same with a topology of {42·5}2{44·510·69·74·8}. The adsorption properties of these MOFs for CO2 and C2 hydrocarbons were then investigated, and the effect of the functional groups was discussed. The results revealed that the introduction of amino and bromo groups could effectively strengthen the adsorption performance.

Potential Applications of Cucurbit[n]urils and Their Derivatives in the Capture of Hazardous Chemicals.

Cucurbit[n]urils (Q[n]s) are a relatively young family of macrocycles, consisting of glycoluril units bridged by methylene groups, and their unique structures have attracted extensive attention from chemists in recent decades. Due to the presence of a rigid hydrophobic inner cavity and two polar outer portals lined with carbonyl groups, Q[n]s not only encapsulate guest species into the cavity, but also coordinate with metal ions/clusters. Considerable achievements have been obtained in the fields of Q[n]s-based host-guest chemistry, coordination chemistry, as well as the combination of host-guest and coordination chemistry. Furthermore, the outer surface of Q[n]s has been demonstrated to be capable of interacting with definite species to generate supramolecular architectures in recent years. With more in-depth research into Q[n]s, their application studies have also emerged as a hot topic. This Minireview focuses on recent advances in the potential applications of solid-state materials based on Q[n]s and their derivatives for the capture and adsorption of hazardous chemicals from a solution or a gas mixture.

Magnetic anisotropy in square pyramidal cobalt(II) complexes supported by a tetraazo macrocyclic ligand.

Two five-coordinate mononuclear Co(ii) complexes [Co(12-TMC)X][B(C6H5)4] (L = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane (12-TMC), X = Cl- (1), Br- (2)) have been studied by X-ray single crystallography, magnetic measurements, high-frequency and -field EPR (HF-EPR) spectroscopy and theoretical calculations. Both complexes have a distorted square pyramidal geometry with the Co(ii) ion lying above the basal plane constrained by the rigid tetradentate macrocyclic ligand. In contrast to the reported five-coordinate Co(ii) complex [Co(12-TMC)(NCO)][B(C6H5)4] (3) exhibiting easy-axis anisotropy, an easy-plane magnetic anisotropy was found for 1 and 2via the analyses of the direct-current magnetic data and HF-EPR spectroscopy. Frequency- and temperature-dependent alternating-current magnetic susceptibility measurements demonstrated that complexes 1 and 2 show slow magnetic relaxation at an applied dc field. Ab initio calculations were performed to reveal the impact of the terminal ligands on the nature of the magnetic anisotropies of this series of five-coordinate Co(ii) complexes.

Coordination polymers with a pyridyl-salen ligand for photocatalytic carbon dioxide reduction.

A new ligand H2L with pyridine and salen moieties and its coordination polymers (CPs) [Mn(L)Cl]·DMF (1) and [Fe(L)Cl]·DMF (2) were synthesized and their photocatalytic activity for the conversion of CO2 into CO under visible-light irradiation was investigated. This is the first instance of pyridyl-salen-ligand based CPs for photocatalyzing CO2 reduction.

Amino group dependent sensing properties of metal-organic frameworks: selective turn-on fluorescence detection of lysine and arginine.

Recently, metal-organic frameworks (MOFs) have been extensively investigated as fluorescence chemsensors due to their tunable porosity, framework structure and photoluminescence properties. In this paper, a well-known Zr(iv)-based MOF, UiO-66-NH2 was demonstrated to have capability for detection of l-lysine (Lys) and l-arginine (Arg) selectively from common essential amino acids in aqueous media via a fluorescence turn-on mechanism. Further investigation reveals its high sensitivity and strong anti-interference properties. Moreover, the possible mechanism for sensing Lys and Arg was explored by FT-IR and 1H-NMR, and the results indicate that the enhancement of the fluorescence could be ascribed to the adsorption of Lys/Arg and the hydrogen bonding interactions between Lys/Arg and the amino group of UiO-66-NH2. The difference of the sensing capacity and sensitivity between UiO-66 and UiO-66-NH2 revealed that the amino group plays an essential role in the sensing performance. This work presents a unique example of the functional group dependent sensing properties of MOFs.

Cucurbit[7]uril-Based Metal-Organic Rotaxane Framework for Dual-Capture of Molecular Iodine and Cationic Potassium Ion.

Metal-organic rotaxane frameworks (MORFs) attracted much attention in the past years for construction of intelligent functional materials. Herein, a one-pot synthesis is reported of a three-dimensional (3D) cucurbit[7]uril (Q[7])-based MORF under hydrothermal conditions, namely Q[7]-MORF-1, formed by encapsulating the anionic benzoate moieties of the tricarboxylate ligand into the cavity of Q[7]. Furthermore, Q[7]-MORF-1 shows dual-capture capacity for iodine and K+ selectively among the alkali metal ions. The captured molecular iodine is included in the cavity of Q[7] through halogen-bonding interactions and the K+ cations are positioned at the carbonyl port of the Q[7] through K-O coordination interactions.

Water-Stable Coordination Polymers as Dual Fluorescent Sensors for Highly Oxidizing Anions Cr2 O7 2- and MnO4.

Due to their striking optical properties, luminescent coordination polymers as sensors for the detection of hazardous species have drawn interest of researchers in consideration of the control of environmental pollution. In this work, the organic ligand 2-(4-((E)-2-(pyridine-2-yl)vinyl)styryl)pyridine (2-bpeb), which possesses a large π-conjugated system, was employed to react with d10 metal ions to obtain novel luminescent coordination polymers. Three complexes [Cd(2-bpeb)0.5 (CNA)(H2 O)] (CP1), [Cd(2-bpeb)0.5 (NDC)] (CP2) and [Zn(2-bpeb)(BDC)] (CP3) were synthesized successfully by introducing carboxylic acids of 4-carboxycinnamic acid (H2 CNA), 2,6-naphthalene dicarboxylic acid (H2 NDC) and 1,4-benzenedicarboxylic acid (H2 BDC) as auxiliary ligands. Because of the existence of the large π-conjugated system and d10 metal ions, all of these coordination polymers exhibit striking fluorescence properties. Impressively, all of them can function as sensors for the detection of highly oxidizing anions MnO4 - and Cr2 O7 2- , with an increased sensitivity for MnO4 - .

Cucurbit[6]uril-based multifunctional supramolecular assemblies: synthesis, removal of Ba(ii) and fluorescence sensing of Fe(iii).

A novel cucurbit[6]uril-based (Q[6]) supramolecular assembly {(NH4)2·Q[6]·(HDTNB)2·2H2O} (1) with a three-dimensional (3D) framework structure was successfully constructed via outer-surface interactions between Q[6] and a flexible aromatic compound, 5,5'-dithiobis-(2-nitrobenzoic acid) (H2DTNB), as a structure-directing agent. It is interesting to find that assembly 1 can selectively capture Ba(ii) cations among the common alkaline-earth metal ions of Mg(ii), Ca(ii), Sr(ii) and Ba(ii), resulting in the formation of an isomorphic 3D assembly {Ba(H2O)2Q[6]}·(HDTNB)2 (2). Furthermore, both assemblies 1 and 2 exhibit the selective sensing of Fe(iii) ions through fluorescence quenching, which has rarely been reported for Q[n]-based supramolecular assemblies.

Zinc(II) and Copper(II) Hybrid Frameworks via Metal-Ion Metathesis with Enhanced Gas Uptake and Photoluminescence Properties.

The fabrication of metal-organic frameworks with controlled structure and desired properties is important but still a challenge. In this work, a zinc(II) framework, {[Zn3(L)2(DABCO)(H2O)]·9DMF} (named as Zn-1), has been synthesized based on [1,1':3',1″-terphenyl]-4,4″,5'-tricarboxylic acid (H3L) and 1,4-diazabicyclo[2.2.2]octane (DABCO), which is isostructural to the previously reported copper(II) analogue, {[Cu3(L)2(DABCO)(H2O)]·15H2O·9DMF} (named as Cu-1). Interestingly, hybrid zinc(II) and copper(II) bimetallic frameworks have been obtained via metal-ion metathesis and found to show enhanced adsorption and photoluminescence properties. Such a post-metal-ion metathesis method can be used to synthesize new and desired frameworks that could not be obtained by direct synthesis.

Metal-organic frameworks with 1,4-di(1H-imidazol-4-yl)benzene and varied carboxylate ligands for selectively sensing Fe(iii) ions and ketone molecules.

Four new metal-organic frameworks (MOFs) [Zn(L)(bpdc)]·1.6H2O (1), [Co(L)(bpdc)]·H2O (2), [Ni3(L)2(bptc)2(H2O)10]·2H2O (3) and [Cd2(L)(Hbptc)2] (4) were achieved by reactions of the corresponding metal salt with mixed organic ligands of 1,4-di(1H-imidazol-4-yl)benzene (L) and 4,4'-benzophenonedicarboxylic acid (H2bpdc) or biphenyl-2,4',5-tricarboxylic acid (H3bptc). They exhibit varied structures: MOFs 1 and 4 are porous three-dimensional (3D) frameworks, while 2 is an infinite one-dimensional (1D) chain and 3 is a two-dimensional (2D) network. Remarkably, 1 and 4 can act as potential fluorescent materials for sensing Fe(iii) ions and different ketone molecules with high selectivity and sensitivity. In addition, MOF 1 shows selective adsorption of CO2 over N2.

Multifunctional Metal-Organic Frameworks with Fluorescent Sensing and Selective Adsorption Properties.

Metal-organic frameworks (MOFs) have attracted great attention in the past years due to their diverse structures as well as interesting properties. However, MOFs with multifunctionality are still challenging. Under solvothermal conditions, reactions of 1,3,5-tris(1-imidazolyl)benzene (tib) and 4,4',4″-benzene-1,3,5-triyl-tribenzoic acid (H3BTB) with Cd(II) salt give rise to two novel MOFs [Cd3(tib)2(BTB)2]·3DEF·4.5H2O (1) and [Cd3(tib)2(BTB)2(DMA)2(H2O)2]·2DMA·8H2O (2) (DEF = N,N-diethylformamide, DMA = N,N-dimethylacetamide) with three-dimensional framework structures. It is fascinating that 1 and 2 not only show unique selectivity for detection of acetone through fluorescence quenching mechanism but also exhibit selective adsorption of gas (CO2 over N2 at 298 K) and dye (methyl orange) molecules.