Benzo-15-crown-5 Research Articles

Geometric and Electronic Structures of Ag+(benzo-18-crown-6), Ag+(dibenzo-18-crown-6), and Ag+(dibenzo-15-crown-5) Complexes Investigated by Cold Gas-Phase Spectroscopy.

The UV photodissociation (UVPD) spectra of Ag+ complexes with benzo-18-crown-6 (B18C6), dibenzo-18-crown-6 (DB18C6), and dibenzo-15-crown-5 (DB15C5) [Ag+(B18C6), Ag+(DB18C6), and Ag+(DB15C5)] are observed under cold gas-phase conditions. Ag+(B18C6) and Ag+(DB18C6) show sharp vibronic bands in the 36000-37200 cm-1 region, while the UVPD spectrum of Ag+(DB15C5) is very broad. These UV bands are assigned to the π-π* transition, which is localized on the B18C6, DB18C6, and DB15C5 part of the complexes. Quantum chemical calculations suggest that the broad UV feature of Ag+(DB15C5) can be attributed to the short lifetimes of optically excited ππ* states due to internal conversion (IC) to low-lying excited states that are present only for this complex. The appearance of the π-π* transition in the same UV region as that of the neutral crown ethers and their complexes with alkali metal ions indicates that the positive charge is localized on the Ag atom in these complexes. However, the fragment ions produced after UV absorption are B18C6+, DB18C6+, and DB15C5+ radical ions, indicating that they are produced via charge transfer (CT) between the Ag+ ion and benzo-crown ethers. The CT during fragmentation is attributed to the higher ionization energy of Ag atom when compared to the benzo-crown ethers. In the complexes, the Ag+ ion is effectively encapsulated by the crown cavity of the benzo-crown ethers without transferring the positive charge from Ag+ to the crown. However, UV excitation of the Ag+(B18C6), Ag+(DB18C6), and Ag+(DB15C5) complexes can reduce the Ag+ ion and produce a Ag atom with high efficiency in the gas phase.

Behavior of Na and K in the extraction process of lithium isotope separation

The extraction behavior of Na and K during lithium isotope separation using benzo-15-crown-5 (B15C5) in chloroform as the extractant was investigated. It was found that potassium was extracted better than sodium and lithium, the metal: B15C5 ratio in the extracted compound was 1: 1 for all metals. It was shown that in the extraction systems with a LiCl concentration higher than 5 mol L-1, B15C5 was noticeably transferred into aqueous solutions, while concentrated LiCl solutions had a salting-out effect with respect to Na and K.

Theoretical prediction of 6Li/7Li separation in solvent extraction system using Urey model

Separation of lithium isotopes (6Li, 7Li) is a key technology to the development and utilization of nuclear energy. In this work, we present an efficient method to theoretically estimate the separation factors of 6Li/7Li in solvent extraction system based on Urey model. The approach was implemented by calculating the equilibrium separation factor of 6Li/7Li in the crown ether/Li aqueous solution [15-crown-5 (15C5), Benzo-15-crown-5 (B15C5), 12-crown-4 (12C4), Dicyclohexyl-18-Crown-6 (DH18C6)/LiX-H2O, X = Cl/I] exchange system utilizing the calculated harmonic vibration frequencies obtained by Density Functional Theory (DFT). The results showed that Urey model can correctly predict the direction of the 6Li/7Li separation as observed in the experiments. With this model, the underlying mechanisms driving the equilibrium isotope separation were elucidated further. The coordination structure of the Li complex played a dominant role in the separation of 6Li/7Li. For the solvent extraction system comprising crown ether phase and LiX aqueous solution, the crown ether with strong ability of excluding the hydrated water of Li gives a higher separation factor. The ways by which Li–O bonding of the Li-crown ether complex can be weakened, such as reducing the coordinated water molecules, applying high polar solvents, performing separation from Li salt with a softer anion, are helpful to improve the separation factor of 6Li/7Li at a fixed temperature. The lithium isotopic exchange is an exothermic reaction. Decreasing temperature favors the exchange reaction. This work is expected to provide guidance for the design of the exchanger and screening of the chemical exchange system for the separation of 6Li/7Li.

Lithium isotope separation by crown ethers of different nitrogen-containing derivatives in the ionic liquid-anisole system

A green and efficient ionic liquid-anisole extraction system was employed for the separation of lithium isotopes by comparing 4‑aminobenzo‑15‑crown‑5 (4‑NH2‑B15C5), 4‑nitrobenzo‑15‑crown‑5 (4‑NO2‑B15C5) and benzo‑15‑crown‑5 (B15C5) extraction agents. The results of the effects of crown ether substituents, crown ether concentration and lithium salt anion on solvent extraction indicated that the molar ratio of crown ether and lithium ion complex is 2:1 and the order of the extraction efficiency in three extraction agents was 4‑NH2‑B15C5 > B15C5 > 4‑NO2‑B15C5. Furthermore, the single-stage separation factor α for 6Li/7Li obtained in present work was 1.032 and maximum abundance of 6Li in organic phase was reached 7.762% in the extraction system of LiI/4‑NO2‑B15C5‑ILs.

Study of the Structure of Lithium Thiocyanate Complexes with Benzo-15-Crown-5 by X-ray Diffraction and IR Spectroscopy

The complex formation of lithium thiocyanate with benzo-15-crown-5 (B15C5) was studied. The possibility of formation of both anhydrous and crystal water-containing complexes was demonstrated. The complexes LiB15C5NCS and LiB15C5H2ONCS were synthesized and characterized by X-ray diffraction and IR spectroscopy.

Effects of Side-Chain Substituents in Benzo-15-Crown-5 on Lithium Extraction

Chloroform–water extraction systems have been studied using crown-ethers as extracting agents, namely: benzo-15-crown-5 (B15C5), 2,3-naphtho-15-crown-5 (N15C5), 4′-nitro-benzo-15-crown-5 (NO2B15C5), 4′-tert-butyl-benzo-15-crown-5 (TBB15C5), and 4′-acetyl-benzo-15-crown-5 (AcB15C5). Extraction isotherms of these systems have been obtained, and an attempt made to elucidate the effect of the structure of extracting agent on extraction characteristics. IR-spectroscopic studies have been performed for selected crown-ethers and their complexes in crystalline form and in chloroform solutions, namely, for N15C5, NO2B15C5, AcB15C5, and B15C5. The complexes LiN15C5H2OClO4 (1), LiN15C5H2OI (2), LiNO2B15C5H2OI (3), LiAcB15C5H2OI (4), and LiTBB15C5H2OI (5) have been isolated for the first time and characterized by IR spectroscopy. Single-crystal X-ray data have been obtained for complexes 1–3.

Controlled architecture of macrocyclic ligand functionalized polymer brushes from glass fibers using surface-initiated ICAR ATRP technique for adsorptive separation of lithium isotopes

By combining surface-initiated atom transfer radical polymerization (SI-ATRP) with mussel-inspired polydopamine (PDA) chemistry, controlled growth of macrocyclic ligands decorated polymer brushes from surfaces of glass fibers was achieved for effective separation of lithium isotopes. Homogenous PDA layer were firstly deposited onto glass fiber mats (GFMs), facilitating the anchoring of ATRP initiators. Propagation of poly(glycidyl methacrylate) (PGMA) brushes from the GFMs were then initiated by using the initiators for continuous activator regeneration (ICAR) ATRP method. The abundant reactive epoxy groups in the PGMA brushes provided an ideal platform for post functionalization of the obtained composites PCGFMs. Benzo-15-crown-5 (B15C5) macrocyclic ligands, with selective binding ability to lithium ions due to the host–guest interaction, were readily introduced to PCGFMs. Adsorption behavior of the functionalized composites PCGFMs-B15C5 toward lithium isotopes was fully investigated. The adsorption of lithium onto PCGFMs-B15C5 fitted Freundlich isotherm model best, and it was a combination of chemisorption and physical adsorption for Li(I) uptake. Kinetics data for Li(I) adsorption was in good agreement with pseudo-second-order rate equation and showed a hybrid rate-limiting process including both film and inter-particle diffusion. The maximum separation factor was 1.037 ± 0.002 and it was independent of both the counter ions and solvents. Softer counter anions and lower polarity solvents in systems were beneficial for higher Li(I) removal but counterintuitive for separation factor. The synthetic strategy established in this work provided an opportunity for broadening functional chromatography extraction substrates for lithium isotopes separation.

Study of lithium complexes with benzo-15-crown-5 ether by X-ray diffraction and IR spectroscopy

The complex formation of lithium with benzo-15-crown-5 (B15C5) was investigated. The complexes LiB15C5H2OX, where X = Cl− (1), I− (2), (3), (5), and LiBF4B15C5 (4) were synthesized and studied by IR spectroscopy. Complexes 1–4 were examined by X-ray diffraction. According to IR spectroscopy data, the crown ether conformation changes upon dissolution. The interaction of the extracted complex with the solvent was identified.

An ion-imprinted material embedded carbon quantum dots for selective fluorometric determination of lithium ion in water samples

An ion-imprinted fluorescent polymer (referred to as CQD@SiO2@IIP) is presented for recognition of lithium ion. The material is based on the use of carbon quantum dots (CQDs) and is prepared by a surface imprinting technique using benzo-15-crown-5 (B15C5) as the complexing agent, methacrylic acid (MAA) as the functional monomer, ethylene glycol dimethacrylate (EGDMA) as the crosslinker, 2,2-azobisisobutyronitrile (AIBN) as the radical initiator, and lithium ion as the template. After optimization of the detection conditions, the relative fluorescence intensity (F0/F), best measured at excitation/emission wavelength of 360 nm/460 nm, varies linearly with the Li+ concentration in the range between 0.5 and 50 μmol·L−1, with a limit of detection of 16 μmol·L−1. Performance was compared to the non-imprinted material, and the imprinting factor is found to be 4.5. The ion-imprinted fluorescence material was applied to the determination of Li+ in (spiked) water samples and obtained good recoveries ranged from 102 to 111.6%.

A Novel Poly(N‐Isopropylacrylamide‐co‐acryloylamidobenzo‐12‐crown‐4) Microgel with Rapid Stimuli‐Responsiveness for Molecule‐Specific Adsorption of γ‐Cyclodextrin

AbstractA novel poly(N‐isopropylacrylamide‐co‐acryloylamidobenzo‐12‐crown‐4) (PNB) microgel with rapid γ‐cyclodextrin (CD)‐responsive characteristics and adsorption property is developed. The microgel is composed of benzo‐12‐crown‐4 (B12C4) units as molecule‐recognition receptors and poly(N‐isopropylacrylamide) networks as phase‐transition actuators as well as adsorbent backbone chains. The PNB microgels significantly increase their volumes induced by γ‐CD, and adsorb γ‐CD molecules within PNB networks because of formation of γ‐CD/B12C4 inclusion complexes. Detection of γ‐CD‐concentration and the molecule‐specific adsorption processes of the microgels are investigated systematically. The PNB microgels provide a new tool for rapid concentration measurement and effective separation of γ‐CD.

Lithium isotopes separation by using benzo-15-crown-5 in eco-friendly extraction system

A green and efficient liquid–liquid extraction system was developed for the separation of lithium isotopes by using hydrophobic ionic liquids (ILs=[C4,6,8,10mim]+[NTf2]−) as extraction organic phase and benzo-15-crown-5 (B15C5) as complexing agent. The maximum single-stage separation factor α of 6Li/7Li obtained in this study was 1.029±0.001, indicating 6Li was enriched in ionic liquid phase while 7Li was concentrated in the aqueous phase. The lithium ion was extracted into the ionic liquid in the formation of 1:2 complex [Li+(B15C5)2]. The negative data of thermodynamic parameters (∆H0 and ∆G0) suggest that the extraction system was a spontaneous exothermic process. In addition, effective lithium isotopes separation factor and the extraction efficiency of lithium ions can be gained in the condition of lower temperature with softer counter anions in the novel extraction system.

Organometallic Chalcones Functioning as Radical Traps: Observations on the Solvated Electron Reduction and the C·H2OH and C·H2Cl Addition Processes. A Time-Resolved, Mechanistic Study.

The pulse radiolysis method was used to investigate reactions between organometallic chalcones derived from ferrocene, cyrhetrene, and cymantrene substituted with a phenyl (R1) or a 4'-benzo-15-crown-5 (B1) moiety and the solvated electron e-sol and two radicals. The principal spectroscopic transformations resolved with the e-sol reactions reveal that the chalcone compounds react under a diffusion controlled condition. The chromophore in the reaction product is the radical anion chalcone, -C(═O)CH═CH-. The kinetics of the redox processes are consistent with the formation of the radical anion in a first step, followed by an E/Z isomerization reaction in the second step. The rate of the E/Z isomerization reaction is dependent on the chalcone substituent. Reactions with C·H2OH and C·H2Cl radicals are strongly affected by the nature of the organometallic fragment. The transient spectra for the reactions between C·H2OH and C·H2Cl radicals with the phenyl-substituted chalcone show weak, broad absorption bands at λob < 400 nm. Only the ferrocenyl derivatives showed an intense absorption band with λmax = 350 nm. The C-centered radicals react with organometallic chalcones with lifetimes less than or equal to a few microseconds, and the products are assigned as adducts of the C-centered radicals to the chalcone.

Gamma‐Cyclodextrin‐Recognition‐Responsive Characteristics of Poly(N‐isopropylacrylamide)‐Based Hydrogels with Benzo‐12‐crown‐4 Units as Signal Receptors

Molecular‐recognition‐responsive characteristics of a novel poly(N‐isopropylacrylamide‐co‐benzo‐12‐crown‐4‐acrylamide) (PNB12C4) hydrogel have been investigated. In the prepared PNB12C4 hydrogel, benzo‐12‐crown‐4 (B12C4) groups act as guest molecules and γ‐cyclodextrin (γ‐CD)‐receptors, and poly(N‐isopropylacrylamide) (PNIPAM) networks act as phase‐transition actuators. The formation of stable γ‐CD/B12C4 complexes enhances the hydrophilicity of the PNB12C4 hydrogel networks, and induces positive shift of the volume phase transition temperature (VPTT) of PNB12C4 hydrogel. Moreover, the PNB12C4 hydrogel also shows thermoresponsive adsorption property selectively towards γ‐CD. The γ‐CD‐recognition sensitivity of PNB12C4 hydrogel can be dramatically improved by increasing γ‐CD concentration in solution or B12C4 content in PNB12C4 copolymer networks. The results in this study provide valuable information for developing crown ether‐based smart materials in various applications. image

Liquid-liquid extraction separation of lithium isotopes by using room-temperature ionic liquids-chloroform mixed solvent system contained benzo-15-crown-5

A novel liquid–liquid extraction system was investigated for the selective separation of lithium isotopes using ionic liquids (ILs=[C6,8,10,12mim]+[PF6]－) as extraction solvent and benzo-15-crown-5 (B15C5) as extractant. The effects of the concentration of lithium salt, counter anion of lithium salt, initial pH of aqueous phase, and extraction temperature on the lithium isotopes separation were studied. The maximum single-stage separation factor α of 6Li/7Li obtained in the present study was 1.038 ± 0.002, indicating the lighter isotope 6Li was enriched in organic phase while the heavier isotope 7Li was concentrated in the aqueous phase. The formation of 2:1 complex Li(B15C5)2+ in the IL phase was determined on the basis of slope analysis method. The large value of the free energy change (−G0=77.87 J mol−1) indicated the high separation capability of the lithium isotopes by B15C5/30%CH3Cl-70% C6mimPF6 mixture extraction system. Lithium in Li(B15C5)2+ complex was stripped by 0.5mol·L−1 HCl solution. The extraction system offers high efficiency, simplicity application prospect to separation lithium isotope separation from LiCl solution.

Conformation of Alkali Metal Ion-Benzo-12-Crown-4 Complexes Investigated by UV Photodissociation and UV-UV Hole-Burning Spectroscopy.

We measure UV photodissociation (UVPD) spectra of benzo-12-crown-4 (B12C4) complexes with alkali metal ions, M(+)·B12C4 (M = Li, Na, K, Rb, and Cs), in the 36300-37600 cm(-1) region. Thanks to the cooling of ions to ∼10 K, all the M(+)·B12C4 complexes show sharp vibronic bands in this region. For UV-UV hole-burning (HB) spectroscopy, we first check if our experimental system works well by observing UV-UV HB spectra of the K(+) complex with benzo-18-crown-6 (B18C6), K(+)·B18C6. In the UV-UV HB spectra of the K(+)·B18C6 complex, gain signals are also observed; these are due to vibrationally hot K(+)·B18C6 complex produced by the UV excitation of cold K(+)·B18C6 complex. Then we apply UV-UV HB spectroscopy to the M(+)·B12C4 complexes, and only one conformer is found for each complex except for the Li(+) complex, which has two conformers. The vibronic structure around the origin band of the UVPD spectra is quite similar for all the complexes, indicating close resemblance of the complex structure. The most stable structures calculated for the M(+)·B12C4 (M = Li, Na, K, Rb, and Cs) complexes also have a similar conformation among them, which coincides with the UVPD results. In these conformers the metal ions are too big to be included in the B12C4 cavity, even for the Li(+) ion. In solution, it was reported that 12-crown-4 (12C4) shows the preference of Na(+) ion among alkali metal ions. From the similarity of the structure for the M(+)·B12C4 complexes, it is suggested that the solvation of free metal ions, not of the M(+)·12C4 complexes, may lead to the selectivity of Na(+) ion for 12C4 in solution.

The role of macrocyclic compounds in the extraction and possible separation of platinum and rhodium from chloride solutions.

Macrocyclic compounds (crown ethers), specifically 18-crown-6 (18-C-6), benzo-15-crown-5 (B-15-C-5), di-benzo-18-crown-6 (DB-18-C-6) and di-cyclohexano-18-crown-6 (DC-18C-6), are used as extractants as well as synergists with amine-group extractants. Platinum and rhodium belong to platinum-group metals (PGMs) and have very similar ionic radii and similar properties. The separation of PGMs is most useful for the preparation of functional materials. Macrocyclic compounds are tested for platinum and rhodium separation and are found to achieve marginal separation. Amines (used as extractants) are paired with macrocyclic compounds (used as synergists), and the separation factor between platinum and rhodium is increased with synergistic enhancement from a chloride solution. The present study discusses extraction chemistry, separation factors and the synergy between platinum and rhodium from chloride solutions. To ensure accurate data, the aqueous samples in this study are analyzed using an inductively coupled plasma optical emission spectrometer (ICP-OES).

Study of isotope effect upon lithium iodide complexation with benzo-15-crown-5 in water–chloroform extraction system

Extraction characteristics of chloroform–water system in lithium iodide extraction with benzo-15-crown-5 (B15C5) were studied. The complexation of the crown ether with LiI in organic phase was shown by IR spectroscopy. Isotope effect multiplication was performed by extraction chromatography technique. The magnitude of isotope separation factor (α) for 6Li-7Li pair was 1.017. The light lithium isotope is concentrated in organic phase.

Synthesis, spectroscopic and spectrophotometric study of BODIPY appended crown ether sensor for ion detection

A novel fluoroionophore compound was synthesized from a boron dipyrromethene (BODIPY) fluorophore and 4′-formylbenzo-15-crown-5 ionophore groups. Photophysical properties of the BODIPY-crown compound were studied with UV–Vis and fluorescence spectroscopy. The effect of metalic cations (Li+, Na+, K+, Mg2+, Ca2+, Ba2+, Al3+, Fe3+, Cu2+, Co2+, Zn2+, Ag+, Hg2+, Pb2+) on the absorption and fluorescence spectra of compound 2 was investigated. Blue shifts were detected in UV–Vis spectra upon addition of some metal ions (Al3+ > Fe3+ > Na+). At the same time, the emission intensity of this complex increased due to binding of Na+ ion to the benzo crown cavity. Additionally, a decrease in the intensity of the 630 nm emission peak and an increase in the intensity of the 570 nm emission peak was observed in the fluorescence emission spectra following addition of Al3+ and Fe3+ ions.

Cocrystals of ammonium perchlorate with a series of crown ethers: preparation, structures, and properties

Three cocrystals of ammonium perchlorate (AP) with a series of crown ethers have been prepared successfully through the solvent/antisolvent method, including 18-crown-6 (18C6), benzo-18-crown-6 (B18C6), and dibenzo-18-crown-6 (DB18C6). Crystal structures of the three cocrystals characterized by single crystal X-ray diffraction (SXD) reveal that all the cocrystals belong to the monoclinic system, in which the space group of the 1 : 1 cocrystal of AP/18C6 and AP/B18C6 is P21/n, P21/c for the 1 : 1.5 cocrystal of AP/DB18C6. The main intermolecular interactions in the three cocrystals are hydrogen bonds and π–π stacking. Powder X-ray diffraction (PXRD) analyses have been performed to scrutinize the purity of all the crystals. The water contact angles of the three cocrystals were measured to be 23.3° (AP/18C6), 25.4° (AP/B18C6), and 75.4° (AP/DB18C6), increasing with the number of phenyl groups connected to the crown ether, and the surface energy of the three cocrystals are greatly decreased compared to AP. The thermal properties of the cocrystals were investigated by thermogravimetry-differential scanning calorimetry (TG-DSC) and hot-stage optical microscopy (HSOM). The results indicate that the decomposition peak temperatures of the three cocrystals are greatly decreased compared to that of pure AP. In particular, the heat release increases from 475.5 J g−1 of AP to 1304.2 J g−1 for AP/B18C6 and 1488.4 J g−1 for AP/DB18C6. So, through carefully choosing the co-former of AP, cocrystallization can comprehensively tune the hygroscopicity and the thermal decomposition property of AP.

UV and IR Spectroscopy of Cold H2O(+)-Benzo-Crown Ether Complexes.

The H2O(+) radical ion, produced in an electrospray ion source via charge transfer from Eu(3+), is encapsulated in benzo-15-crown-5 (B15C5) or benzo-18-crown-6 (B18C6). We measure UV photodissociation (UVPD) spectra of the (H2O·B15C5)(+) and (H2O·B18C6)(+) complexes in a cold, 22-pole ion trap. These complexes show sharp vibronic bands in the 35 700-37 600 cm(-1) region, similar to the case of neutral B15C5 or B18C6. These results indicate that the positive charge in the complexes is localized on H2O, giving the forms H2O(+)·B15C5 and H2O(+)·B18C6, in spite of the fact that the ionization energy of B15C5 and B18C6 is lower than that of H2O. The formation of the H2O(+) complexes and the suppression of the H3O(+) production through the reaction of H2O(+) and H2O can be attributed to the encapsulation of hydrated Eu(3+) clusters by B15C5 and B18C6. On the contrary, the main fragment ions subsequent to the UV excitation of these complexes are B15C5(+) and B18C6(+) radical ions; the charge transfer occurs from H2O(+) to B15C5 and B18C6 after the UV excitation. The position of the band origin for the H2O(+)·B18C6 complex (36323 cm(-1)) is almost the same as that for Rb(+)·B18C6 (36315 cm(-1)); the strength of the intermolecular interaction of H2O(+) with B18C6 is similar to that of Rb(+). The spectral features of the H2O(+)·B15C5 complex also resemble those of the Rb(+)·B15C5 ion. We measure IR-UV spectra of these complexes in the CH and OH stretching region. Four conformers are found for the H2O(+)·B15C5 complex, but there is one dominant form for the H2O(+)·B18C6 ion. This study demonstrates the production of radical ions by charge transfer from multivalent metal ions, their encapsulation by host molecules, and separate detection of their conformers by cold UV spectroscopy in the gas phase.