Phase Transformations in Alkaline and Acid Leached Y Zeolites Dealuminated by Steaming

The steaming of zeolite Y (here at 873 K for 7 hours) leads to the formation of an amorphous aluminium aluminosilicate in addition to the dealuminated zeolite (DAY). An alkaline treatment of DAY causes the transformation of the non‐framework phase into an alkali aluminosilicate and the partial desilication of the DAY framework. The alkali aluminosilicate is decomposed by a moderate acid leaching under the formation of silica gel. The ²⁹Si MAS NMR and IR spectra of DAY and its chemically treated modifications are superimposed by the signals of the crystalline zeolite framework and the amorphous non‐framework materials whereas XRD measurements only characterize the current state of the framework.     

Aluminum-27 NMR Investigations of Aqueous and Methanolic Aluminosilicate Solutions

Aluminum-27 NMR spectroscopy was used to characterize aqueous and methanolic alkaline solutions of tetramethylammonium (TMA) aluminosilicates. Aluminosilicate solutions have been prepared with different concentrations of silicon [0.577–1.24% (w/w)], aluminum [0.0022–0.239% (w/w)], methanol [0.0–0.70% (w/w)] and H₂O [0.23–90% (w/w)]. All solutions contain the same ratio of Si/TMA = 1 and Si/Al molar ratios between 0.5 and 25.²⁷Al NMR spectra of TMA aluminosilicate solutions are characterized by a variety of aluminosilicate species such as q¹(Al1OSi), q²(Al2OSi), q³(Al3OSi) and q⁴(Al4OSi). Aluminum-27 NMR spectra of TMA aluminosilicate solutions indicate that considerable changes occurred by changing the Si/Al ratio. The distribution of aluminosilicate species was affected by the presence of the methanol and the method of mixing the silicate and aluminosilicate solutions. A methanolic aluminosilicate solution needs about twice the time required for an aqueous aluminosilicate solution to reach a steady state, i.e., the latter takes 36 h to reach steady state. Results with the same concentration of silicon and aluminum show that the formation and distribution of aluminosilicate species are strongly dependent on the solvent comprising the silicate and aluminate solutions.     

Pseudo cyclic ionophores: ‘Binary-effect’ of quinolinyloxy groups at both ends of oligoethylene glycols on the conformational stabilization of their complexes with alkali metal salts

A series of noncyclic neutral ionophores has been synthesized by the reaction of oligoethylene glycol dihalides with 8-quinolinol. Complexation properties for alkali metal picrates were evaluated from solvent extraction and bulk liquid membrane transport experiments. Complexation profiles of the newly synthesized ionophores with a hexyl chain were similar to those of their homologues without the hexyl chain in the extraction experiments. Among them, the pentaethylene glycol derivatives showed the highest extraction efficiency and selectivity towards potassium ion. From the¹H NMR spectra (400 MHz), the change in chemical shifts of the aromatic protons upon the addition of alkali metal thiocyanates suggested the existence of a stabilization effect which is caused by intramolecular stacking conformations between the quinoline rings during complexation. Aryl stacking interactions depend on the size of the cations and on the chain length of the oligoethylene glycol. The relationship between transport ability towards alkali metal cations and lipophilicity of these ionophores is also discussed.     

Characterization of potassium and sodium-potassium alloy solutions containing metal anions and complexed cations by means of NMR and ESR techniques

The influence of a complexing agent, kind of solvent and temperature on the stability and ionic composition of potassium and sodium-potassium alloy solutions containing metal anions and complexed cations as well as solvated electrons are discussed basing on the analysis of alkali metal NMR and ESR spectra. Surprisingly it seems that the stability of metal solutions in tetrahydrofuran at ambient temperature is inversely proportional to the durability of K+ complex in the case of five studied ligands. The most stable metal solutions were obtained using 15-crown-5. It was shown that the characteristic blue colour of metal solutions is not connected with the presence of solvated electrons but with metal anions.     

Factor analysis of 27Al MAS NMR spectra for identifying nanocrystalline phases in amorphous geopolymers

Nanostructured materials offer enhanced physicochemical properties because of the large interfacial area. Typically, geopolymers with specifically synthesized nanosized zeolites are a promising material for the sorption of pollutants. The structural characterization of these aluminosilicates, however, continues to be a challenge. To circumvent complications resulting from the amorphous character of the aluminosilicate matrix and from the low concentrations of nanosized crystallites, we have proposed a procedure based on factor analysis of ²⁷Al MAS NMR spectra. The capability of the proposed method was tested on geopolymers that exhibited various tendencies to crystallize (i) completely amorphous systems, (ii) X‐ray amorphous systems with nanocrystalline phases, and (iii) highly crystalline systems. Although the recorded ²⁷Al MAS NMR spectra did not show visible differences between the amorphous systems (i) and the geopolymers with the nanocrystalline phase (ii), the applied factor analysis unambiguously distinguished these materials. The samples were separated into the well‐defined clusters, and the systems with the evolving crystalline phase were identified even before any crystalline fraction was detected by X‐ray powder diffraction. Reliability of the proposed procedure was verified by comparing it with ²⁹Si MAS NMR spectra. Factor analysis of ²⁷Al MAS NMR spectra thus has the ability to reveal spectroscopic features corresponding to the nanocrystalline phases. Because the measurement time of ²⁷Al MAS NMR spectra is significantly shorter than that of ²⁹Si MAS NMR data, the proposed procedure is particularly suitable for the analysis of large sets of specifically synthesized geopolymers in which the formation of the limited fractions of nanocrystalline phases is desired. Copyright © 2013 John Wiley & Sons, Ltd.     

Water Dynamics in Highly Concentrated Salt Solutions: A Multi-Nuclear NMR Approach

Living cells often contain compartments with high concentration of charged biomolecules. A key question pertinent to the function of biomolecules is how water dynamics are affected by interaction with charged molecules. Here, we study the dynamical behavior of water in an extreme condition, that is, in saturated salt solutions, where nearly all water molecules are located within the first hydration layer of ions. To facilitate disentangling the effects of cations and anions, our study is focused on alkali chloride solutions. Following a multi-nuclear NMR approach enabling direct monitoring of protons and the quadrupolar nuclei ⁷Li, ¹⁷O, ²³Na, ³⁵Cl, ⁸⁷Rb and ¹³³Cs, we investigate how the translational and rotational mobility of water molecules, chloride anion and corresponding cations are affected within the constrained environment of saturated solutions. Our results indicate that water molecules preserve a large level of mobility within saturated alkali chloride solutions that is significantly independent of adjacent ions.     

Synthesis, NMR characterization and ion binding properties of 1,3-bridged p-tert-butyldihomooxacalix[4]crown-6 bearing pyridyl pendant groups

1,3-Di(2-pyridylmethoxy)-p-tert-butyldihomooxacalix[4]arene-crown-6 (2) was synthesized for the first time. 2 was isolated in a cone conformation in solution at room temperature, as established by NMR spectroscopy (¹H, ¹³C and NOESY). Complete assignment of both proton and carbon NMR spectra was achieved by a combination of COSY, HSQC and HMBC experiments. The binding properties of ligand 2 towards alkali, alkaline earth, transition and heavy metal cations have been assessed by phase transfer and proton NMR titration experiments. The results are compared to those obtained with other dihomooxacalix[4]arene-crowns-6 and closely-related calix[4]arene-crown derivatives. 2 shows a preference for the soft heavy metal cations (except for Cd²⁺), with a very strong affinity for Ag⁺. Some transition metal cations are also well extracted. 2 forms 1:1 complexes with K⁺, Ca²⁺ and Ag⁺, and ¹H NMR titrations indicate that they should be encapsulated into the cavity defined by the crown ether unit and by the two pyridyl pendant arms. A 1:2 (ML₂) complex is formed with Zn²⁺ and two species, probably 1:1 and 1:2 complexes, are obtained with Pb²⁺.     

A New Extraction System Based on Isopropyl Salicylate and Trioctylphosphine Oxide for Separating Alkali Metals

It was established that isopropyl salicylate can be used similarly to 1,3-diketones as a key component for a new efficient extraction system for selective separation of alkali metal cations. According to DFT modeling of complexes of isopropyl salicylate and 1,3-diketone with alkali metal cations (Li⁺, Na⁺, K⁺), six-membered metallacycles are formed whose stability decreases along the series Li > Na > K, which results in the observed enhanced affinity to lithium. The extraction ability of isopropyl salicylate is manifested in the presence of trioctylphosphine oxide (TOPO). The newly obtained complexes of isopropyl salicylate with alkali metal cations as well as their extracts in a mixture with TOPO are characterized by means of FT-IR, Raman, and NMR spectroscopy. The probable structure of the extracted lithium complex is presumed and the role of TOPO in the extraction process is investigated in detail. Extraction experiments showed extremely high separation coefficients for Li/Na and Li/K pairs in the extraction from a model multi-component solution.     

Experimental (FT-IR, FT-Raman, H, C NMR) and theoretical study of alkali metal 2-aminonicotinates

The influence of lithium, sodium, potassium, rubidium and cesium on the electronic system of 2-aminonicotinic acid (2-ANA) was studied by the methods of molecular spectroscopy. The vibrational (FT-IR, FT-Raman) and NMR (¹H and ¹³C) spectra of 2-aminonicotinic acid and its alkali metal salts were recorded. Characteristic shifts and changes in intensities of bands along the metal series were observed. The changes of chemical shifts of protons (¹H NMR) and carbons (¹³C NMR) in the series of studied alkali metal 2-aminonicotinates (2-AN) were observed too.Optimized geometrical structures of the studied compounds were calculated by the B3LYP method using the 6-311++G** basis set. Aromaticity indices, atomic charges, dipole moments and energies were also calculated. The theoretical chemical shifts in ¹H and ¹³C NMR spectra and theoretical wavenumbers and intensities of IR and Raman spectra were determined. The calculated parameters were compared to the experimental characteristics of the studied compounds.     

Pulse radiolysis of alkali metal cations in isopropylamine: Correlation of optical absorption spectra with electron spin resonance data

Pulse radiolysis of alkali metal cations in isopropylamine indicates the formation of three distinct optical bands attributed to solvated electrons, e^?_s, ion-pairs (M⁺, e^?_s) and alkali anions M^?. It is found that the ion-pair spectra exhibit a distinct blue shift from that of e^?_s. Comparisons with results obtained in ethylamine, tetrahydrofuran and other solvents demonstrate that the position of the ion-pair band can be correlated with the percent atomic character observed by ESR for the “monomer” species in alkali metal solutions. Results are presented for the alkali metal series, Li, Na, K, Rb and Cs.     

A Study of Transition‐Metal Organometallic Complexes Combining 35Cl Solid‐State NMR Spectroscopy and 35Cl NQR Spectroscopy and First‐Principles DFT Calculations

A series of transition‐metal organometallic complexes with commonly occurring metal? chlorine bonding motifs were characterized using ³⁵Cl solid‐state NMR (SSNMR) spectroscopy, ³⁵Cl nuclear quadrupole resonance (NQR) spectroscopy, and first‐principles density functional theory (DFT) calculations of NMR interaction tensors. Static ³⁵Cl ultra‐wideline NMR spectra were acquired in a piecewise manner at standard (9.4 T) and high (21.1 T) magnetic field strengths using the WURST‐QCPMG pulse sequence. The ³⁵Cl electric field gradient (EFG) and chemical shielding (CS) tensor parameters were readily extracted from analytical simulations of the spectra; in particular, the quadrupolar parameters are shown to be very sensitive to structural differences, and can easily differentiate between chlorine atoms in bridging and terminal bonding environments. ³⁵Cl NQR spectra were acquired for many of the complexes, which aided in resolving structurally similar, yet crystallographically distinct and magnetically inequivalent chlorine sites, and with the interpretation and assignment of ³⁵Cl SSNMR spectra. ³⁵Cl EFG tensors obtained from first‐principles DFT calculations are consistently in good agreement with experiment, highlighting the importance of using a combined approach of theoretical and experimental methods for structural characterization. Finally, a preliminary example of a ³⁵Cl SSNMR spectrum of a transition‐metal species (TiCl₄) diluted and supported on non‐porous silica is presented. The combination of ³⁵Cl SSNMR and ³⁵Cl NQR spectroscopy and DFT calculations is shown to be a promising and simple methodology for the characterization of all manner of chlorine‐containing transition‐metal complexes, in pure, impure bulk and supported forms.     

Improved Large‐Scale Liquid‐Phase Synthesis and High‐Temperature NMR Characterization of Short ­(F‐)PNAs

We report on a large‐scale synthesis of F‐PNA trimer 10 and PNA trimer 11 . The key improvement is the facile two‐step synthesis of (2,4‐difluoro‐5‐methylphenyl)acetic acid ( 2 ). Water solubility of the corresponding F‐PNA oligomer 10 was achieved by synthesizing solubility enhancer 5a , which is twofold positively charged and only consists of inherent structural elements of PNA. Protected and unpaired PNA n‐mers exist in a mixture of 2ⁿ conformers undergoing slow exchange and leading to complicated NMR spectra. Structure analysis was improved by recording ¹H‐ and ¹³C‐NMR spectra at elevated temperatures above the coalescence point. Fully protected backbone derivatives show sharp resonances where expected, and spectra of protected PNAs are remarkably simplified, thereby allowing an interpretation for the first time. Both trimers 10 and 11 are considered as building blocks for a self‐replicating system based on PNA.     

Statistical Approach for the Determination of the Stereoregularity of Optically Active Propylene–CO Copolymers

A two‐parameter statistic model was applied to analyze the NMR spectra of a series of stereoregular propylene–CO copolymers synthesized by catalytic polymerization in the presence of various transition‐metal complexes containing chiral ligands. The concentration of the different pentads, estimated to be recognizable in the spectra, was determined. A tentative assignment of the nature of the different peaks composing the signal of the C?O group in the ¹³C‐NMR spectra is proposed.     

Lithium-7, sodium-23, and cesium-133 NMR and far infrared study of alkali complexes with C222-dilactam in various solvents

Nuclear magnetic resonances of alkali nuclei,⁷Li,²³Na, and¹³³Cs, as well as far infrared measurements are used to study alkali complexes of a bicyclic diazapolyoxa ligand—the dilactam of cryptand C222. Measurements were carried out in pyridine, tetrahydrofuran, acetonitrile, nitromethane, dimethylformamide, and aqueous solutions. The complexing ability of the dilactam is similar to, but weaker than, that of the cryptand C222. The limiting chemical shifts of the complexed cations were solvent-dependent, indicating incomplete enclosure of the cation by the ligand. Formation constants of Li⁺ and Cs⁺ complexes were calculated from the chemical-shift dependence on the ligand/metal ion mole ratio.     

Molecular structure of 3-aminobenzoic acid complexes with alkali metals

The vibration (FT-IR, FT-Raman), electronic (UV-Vis) and NMR (1H and 13C) spectra for 3-aminobenzoic acid and its alkali metal salts were recorded. The influence of lithium, sodium, potassium, rubidium and cesium on the electronic system of the 3-aminobenzoic acid was studied. The assignment of the vibration spectra was done. Characteristic shifts of band wavenumbers and changes in band intensities along the metal series were observed. Good correlation between the wavenumbers of the vibrational bands in the IR and Raman spectra for 3-aminobenzoates and ionic potential, electronegativity, atomic mass and affinity of metal cations were found. The chemical shifts of protons (1H NMR) and carbons (13C NMR) in the series of studied alkali metals were also observed. Optimized geometrical structures of studied compounds were calculated by ab initio and density functional methods.     

Solid‐State 17O NMR Spectroscopy of Paramagnetic Coordination Compounds

High‐quality solid‐state ¹⁷O (I=5/2) NMR spectra can be successfully obtained for paramagnetic coordination compounds in which oxygen atoms are directly bonded to the paramagnetic metal centers. For complexes containing V^III (S=1), Cu^II (S=1/2), and Mn^III (S=2) metal centers, the ¹⁷O isotropic paramagnetic shifts were found to span a range of more than 10 000 ppm. In several cases, high‐resolution ¹⁷O NMR spectra were recorded under very fast magic‐angle spinning (MAS) conditions at 21.1 T. Quantum‐chemical computations using density functional theory (DFT) qualitatively reproduced the experimental ¹⁷O hyperfine shift tensors.     

Synthesis,Structure, Spectroscopic Studies,and Complexation of Novel Crown Ether Butadienyl Dyes

Butadienyl dyes of the benzothiazole series with various fragments of benzocrown ethers 1a – c were synthesized for the first time. The structures and spectral properties of crown‐containing butadienyl dyes and their complexes with alkali and alkaline‐earth metal cations were studied by X‐ray diffraction analysis and ¹H‐NMR, UV/VIS, and resonance Raman spectroscopy. To interpret the experimental results, quantum‐chemical calculations were performed. In the case of Sr²⁺ and Ba²⁺ ions, the formation of strong sandwich complexes [M( 1b )₂]²⁺ of an unusual structure involving stacking interactions was established; the dye molecules are arranged one above another in the complex according to the ‘head‐to‐head' pattern.     

Complete assignments of NMR data of salens and their cobalt (III) complexes

Salens, derived from 1,2‐ethylenediamine and salicylaldehydes, have been widely used as ligands for metal complexes which have been showing enormous potential in chemical properties of asymmetric catalysts as well as biological properties such as anticancer agents. Almost all of the salen–metal complexes with their corresponding metal (II)‐complexes show the evidences of chelation of two oxygens in salens. However, several metal (II) complexes, especially cobalt (II) complexes, could not show NMR spectra due to their paramagnetism. Recently, it has been reported that one of the cobalt (III) complexes was used for NMR spectroscopy to evaluate its stereoselectivity as a catalyst. Even though many salen ligands are known, their NMR data are not assigned completely. It was possible that modification in northern part of salen with 2‐hydroxyphenyl group afforded another oxygen chelation site in salen ligand. Here we report that synthesis and full NMR assignment of new salen ligands, which form meso 1,2‐bis(2‐hydroxyphenyl)ethylenediamine) and their cobalt (III) complexes. The assignments of ¹H and ¹³C NMR data obtained in this experiment can help us to predict the NMR data of other salen ligands. Copyright © 2008 John Wiley & Sons, Ltd.     

Influence of alkaline earth metals on molecular structure of 3-nitrobenzoic acid in comparison with alkali metals effect

The influence of beryllium, magnesium, calcium, strontium and barium cations on the electronic system of 3-nitrobenzoic acid was studied in comparison with studied earlier alkali metal ions [1]. The vibrational FT-IR (in KBr and ATR techniques) and ¹H and ¹³C NMR spectra were recorded for 3-nitrobenzoic acid and its salts. Characteristic shifts in IR and NMR spectra along 3-nitrobenzoates of divalent metal series Mg → Ba were compared with series of univalent metal Li → Cs salts. Good correlations between the wavenumbers of the vibrational bands in the IR spectra for 3-nitrobenzoates and ionic potential, electronegativity, inverse of atomic mass, atomic radius and ionization energy of metals were found for alkaline earth metals as well as for alkali metals. The density functional (DFT) hybrid method B3LYP with two basis sets: 6-311++G** and LANL2DZ were used to calculate optimized geometrical structures of studied compounds. The theoretical wavenumbers and intensities of IR spectra as well as chemical shifts in NMR spectra were obtained. Geometric aromaticity indices, atomic charges, dipole moments and energies were also calculated. The calculated parameters were compared to experimental characteristic of studied compounds.     

Electrochemistry and Ion Sensing Properties of Conducting Hydrogel Layers Based on Polypyrrole and Alkoxysulfonated Poly(3,4‐ethylenedioxythiophene) (PEDOT‐S)

Acidic aqueous solutions containing pyrrole and alkoxysulfonated PEDOT derivative (PEDOT‐S) were found to undergo polymerization in the absence of an external oxidizing agent. The product was a nearly black‐colored conducting hydrogel that after separation could be dispersed in water or acetone. The suspensions could be used to deposit cast films on a polycrystalline gold electrode. The polymer modified electrode showed a nearly Nernstian potentiometric response to Ag⁺ cations in the concentration range of 10^?5–10^?1 M with the slope of 54 mV/decade. The response was specific to Ag⁺ compared to a series of alkali and transition‐metal cations (pK_Ag/M>3.7).