Molecular dynamics simulation on ion-pair association of NaCl from ambient to supercritical water

Molecular dynamics (MD) simulations for aqueous NaCl solution were performed from ambient to supercritical conditions (25 °C, 1.0 g cm⁻³; 250–350 °C, 0.67–0.8 g cm⁻³; 380 °C, 0.2–0.8 g cm⁻³; and 400–600 °C, 0.4 and 0.7 g cm⁻³) in the canonical ensemble to examine how the hydration structure relates with the thermodynamics of the ion-pair association. Hydration structure and the potential of mean force (PMF) of Na⁺Cl⁻ ion-pair were calculated. Ion-pair association constants were also calculated from the PMFs. Energies and entropies of the ion-pair at arbitrary inter-ionic distances from 2.0 to 8.0 Å were evaluated from the temperature derivative of the PMFs. From the calculation of energies and entropies, Na⁺–Cl⁻ pair association was found to be endothermic and promoted by the entropy gain. PMFs had minimums and a slight maximum corresponding to CIP, SShIP, and the transition state between CIP and SShIP, and similar minimums and maximum were only observed for the energy term and not clearly observed for the entropy term. This result indicates that the shape of the PMF and stability of SShIP are determined by the energy of the system. Relationship between the hydration structure and the energy of the system was examined and it was confirmed that the hydration structure in the first hydration shell of the ion-pair was one of the important factor, which made the minimums and maximum in the energy terms and PMFs, and stabilized the SShIP structure.     

Insight into the cation–anion interaction in 1,1,3,3-tetramethylguanidinium lactate ionic liquid

In order to deepen the understanding of cation–anion interaction in ionic liquids (ILs), the structure and interionic interaction of 1,1,3,3-tetramethylguanidinium lactate ([tmg][L]) ion pair, including stable configuration, hydrogen bond, frontier molecular orbital, electron density, ion interaction energy and charge transfer, are studied by using ab initio calculations. It is found that more charge-localized character of [tmg][L], especially the C1 carbocation on [tmg]⁺, and the intermolecular –NH₂-associated hydrogen bonds can substantially increase the cation–anion interaction, the interaction energy is 65.3–109.3 kJ/mol higher than that of 1-n-butyl-3-methylimidazolium-based ILs. It is also found that the frontier molecular orbitals, i.e., the HOMO, HOMO + 1 of [L]⁻ and the LUMO, LUMO + 1 of [tmg]⁺, can effectively interact and more charges are transferred between cation and anion. Based on the above results, the physical property of ILs is discussed.     

Aluminum phosphate dispersed on a cellulose acetate fiber surface: Preparation, characterization and application for Li, Na and K separation

Cellulose acetate fibers with supported highly dispersed aluminum phosphate were prepared by reacting aluminum-containing cellulose acetate (Al₂O₃=3.5 wt.%; 1.1 mmol g⁻¹ aluminum atom per gram of the material) with phosphoric acid. Solid-state NMR spectra (CPMAS ³¹P NMR) data indicated that HPO₄²⁻ is the species present on the fiber surface. The specific concentration of acidic centers, determined by ammonia gas adsorption, is 0.50 mmol g⁻¹. The ion exchange capacities for Li⁺, Na⁺ and K⁺ ions were determined from ion exchange isotherms at 298 K and showed the following values (in mmol g⁻¹): Li⁺=0.03, Na⁺=0.44 and K⁺=0.50. The H⁺/Li⁺ exchange corresponds to the model of the ideal ion exchange with a small value of the corresponding equilibrium constant K=1.1×10⁻². Due to the strong cooperative effect, the H⁺/Na⁺ and H⁺/K⁺ ion exchange is non-ideal. These ion exchange equilibria were treated with the use of models of fixed bi- or tridentate centers, which consider the surface of the sorbent as an assemblage of polyfunctional sorption centers. Both the observed ion exchange capacities with respect to the alkaline metal ions and the equilibrium constants were discussed by taking into consideration the sequence of the ionic hydration radii for Li⁺, Na⁺ and K⁺. The matrix affinity order for the ions decreases as the hydration radii of the cations increase, i.e. Li⁺>Na⁺>K⁺. The high values of the separation factors S_Na⁺/Li⁺ and S_K⁺/Li⁺ (up to several hundred) provide quantitative separation of Na⁺ and K⁺ from Li⁺ from a mixture containing these three ions.     

(27)Al NMR and Raman spectroscopic studies of alkaline aluminate solutions with extremely high caustic content - Does the octahedral species Al(OH)(6)(3-) exist in solution?

²⁷Al NMR and Raman spectra of alkaline aluminate solutions with 0.005 M ≤ [Al(III)]_T ≤ 3 M in various M′OH solutions (M′⁺ = Na⁺, K⁺ and Li⁺) were recorded and analysed. Caustic concentrations up to 20 M were used to explore whether higher aluminium hydroxo complexes are formed at extremely high concentrations of hydroxide. A single peak was observed on the ²⁷Al NMR spectrum of each solution. The chemical shift of this peak shifts significantly upfield with increasing [M′OH]_T in solutions with [Al(III)]_T < 0.8 M. This variation shows a strong dependence on the cation of the solution and practically disappears in systems with [Al(III)]_T ≥ 0.8 M. For Raman spectra of solutions with [Al(III)]_T = 0.8 M and [NaOH]_T ≥ 10 M, the peak maximum of the symmetric ν₁-AlO₄ stretching of Al(OH)₄⁻ shifted progressively from ∼620 to ∼625 cm⁻¹ and decreased in intensity with increasing [NaOH]_T. In parallel, modes centred at ∼720 and ∼555 cm⁻¹ (cf. ∼705 and ∼535 cm⁻¹ at lower [NaOH]_T, ascribed to a dimeric aluminate species appeared, and their intensities increased with increasing [NaOH]_T. These variations in the ²⁷Al NMR and Raman spectra can be interpreted in terms of contact ion-pairs formed between the cation of the medium and the well-established Al(OH)₄⁻ or the dimeric aluminate species. Assumption of higher aluminium hydroxo complex species (e.g., Al(OH)₆³⁻) is not necessary to explain the spectroscopic effects observed.     

A novel series of iridium complexes with alkenylquinoline ligands: Theoretical study on electronic structure and spectroscopic property

The ground and the lowest-lying triplet excited state geometries, electronic structures, and spectroscopic properties of a novel series of neutral iridium(III) complexes with cyclometalated alkenylquinoline ligands [(C^N)₂Ir(acac)] (acac = acetoylacetonate; C^N = 2-[(E)-2-phenyl-1-ethenyl]pyridine (pep) 1; 2-[(E)-2-phenyl-1-ethenyl]quinoline (peq) 2; 1-[(E)-2-phenyl-1-ethenyl]isoquinoline (peiq) 3; 2-[(E)-1-propenyl]pyridine (pp) 4; 2-[(E)-1-fluoro-1-ethenyl]pyridine (fpp) 5) were investigated by DFT and CIS methods. The highest occupied molecular orbital is composed of d(Ir) and π(C^N) orbital, while the lowest unoccupied molecular orbital is dominantly localized on C^N ligand. Under the TD-DFT with PCM model level, the absorption and phosphorescence in CH₂Cl₂ media were calculated based on the optimized ground and triplet excited state geometries, respectively. The calculated lowest-lying absorptions at 437 nm (1), 481 nm (2), 487 nm (3), 422 nm (4), and 389 nm (5) are attributed to a {[d_x²-y²(Ir) + d_xz(Ir) + π(C^N)] → [π∗(C^N)]} transition with metal-to-ligand/intra-ligand charge transfer (MLCT/ILCT) characters, and the calculated phosphorescence at 582 nm (1), 607 nm (2), 634 nm (3), 515 nm (4), and 491 nm (5) can be described as originating from the ³{[d_x²-y²(Ir) + d_xz(Ir) + π (C^N)] [π∗(C^N)]} excited state with the ³MLCT/³ILCT characters. The calculated results revealed that the phosphorescent color of these new Ir(III) complexes can be tuned by changing the π-conjugation effect strength of the C^N ligand.     

Kinetics of styrene emulsion polymerization in the presence of montmorillonite

The effect of the pristine sodium montmorillonite (Na⁺-MMT) on the styrene emulsion polymerizations with different concentrations of SDS ([SDS]) was investigated. At constant [SDS], the polymerization rate is faster for the run with 1 wt.% Na⁺-MMT compared to the counterpart without Na⁺-MMT. Micelle nucleation predominates in the polymerizations with [SDS] ≧ 13 mM. On the other hand, the contribution of the polymerization associated with the Na⁺-MMT platelets increases significantly when [SDS] decreases from 13 to 9 mM. At [SDS] (e.g., 2 mM) < CMC, homogeneous nucleation controls the particle formation process and polymerization kinetics. Moreover, the contribution of the Na⁺-MMT platelets that act as extra reaction loci to the polymerization kinetics is even comparable to the run in the absence of Na⁺-MMT. The resultant polymer particle size, polymer molecular weight and zeta potential were characterized and a preliminary model was developed to qualitatively study the differences between the polymerizations in the presence and absence of 1 wt.% Na⁺-MMT.     

Synthesis, characterization, thermal stability and electrochemical properties of poly-4-[(2-methylphenyl)iminomethyl]phenol

In this study, the reaction conditions of poly-4-[(2-methylphenyl)iminomethyl]phenol (P-2-MPIMP) were studied by using oxidants such as air O₂, H₂O₂ and NaOCl in an aqueous alkaline medium between 50 and 90 °C. The structures of the synthesized monomer and polymer were confirmed by FT-IR, UV-vis, NMR and elemental analysis. The characterization was made by TG-DTA, size exclusion chromatography (SEC) and solubility tests. At the optimum reaction conditions, the yield of poly-4-[(2-methylphenyl)iminomethyl]phenol (P-2-MPIMP) was found to be 20% (for air O₂ oxidant), 33% (for H₂O₂ oxidant), and 74% (for NaOCl oxidant). According to the SEC analysis, the number-average molecular weight (M_n), weight-average molecular weight (M_w) and polydispersity index (PDI) values of P-2-MPIMP were found to be 3300, 4100 g mol⁻¹ and 1.242, using H₂O₂, and 4550, 5150 g mol⁻¹and 1.132, using air O₂ and 5300, 5850 g mol⁻¹ and 1.104, using NaOCl, respectively. According to TG analysis, the weight losses of 4-[(2-methylphenyl)iminomethyl]phenol (2-MPIMP) and P-2-MPIMP were found to be between 75.29% and 48.17% at 1000 °C, respectively. P-2-MPIMP was shown to have a higher stability against thermal decomposition. Also, electrical conductivity of the P-2-MPIMP was measured, showing that the polymer is a typical semiconductor. Electrochemically, the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO) and electrochemical energy gaps ( of 2-MPIMP and P-2-MPIMP were found to be −6.01, −6.03; −2.63, −2.82; 3.38 and 3.21 eV, respectively. According to UV-vis measurements, the optical band gap (E_g) of 2-MPIMP and P-2-MPIMP was found to be 3.40 and 2.97 eV, respectively.     

Synthesis of molybdenocene(IV) and tungstenocene(IV) tropolonato complexes: Its derivative containing calix[4]arene moiety

The cationic di-μ-hydroxo dinuclear complexes of molybdenocene and tungstenocene [Cp₂M(μ-OH)₂MCp₂]⁺ (Cp = η-C₅H₅; M = Mo or W) react with tropolone to afford corresponding tropolonato complexes [Cp₂M(trop)]⁺ (trop = C₇H₅O₂). The products were investigated by IR, ¹H NMR, and ¹³C NMR spectroscopy as well as by X-ray crystallography (M = W). The structure shows that the central metal is surrounded by a distorted tetrahedral array of the two centers of cyclopentadienyl ligands and the two oxygen atoms of tropolonato ligand. The reaction has been extended to the synthesis of calix[4]arene receptor functionalized at the 1,3-positions of the upper rim with two tropolonato-molybdenocene centers.     

A study on interaction of Be, Mg and Ca with phenylalanine: Binding energies, metal ion affinities and IR signature of complex stability

The interaction between divalent metal cations and amino acids plays an important role in many biological processes. In present report, we have examined the effect of metal cations (Be⁺⁺, Mg⁺⁺ and Ca⁺⁺) interaction on structures, binding energies (BE), metal ion affinities (MIA) and infrared (IR) spectra of phenylalanine (Phe) molecule by density functional theory (DFT) calculations at B3LYP/6-311++G(d,p) level. Nine different ground state isomers of Phe molecule have been optimized at B3LYP/6-311++G (d,p) level of theory. The relative ground state energies of these nine isomers are lying between 0.0-1.9 kcal/mol with respect to the ground state energy of most stable Phe isomer. Seven most stable complexes of Phe molecule with Be⁺⁺, Mg⁺⁺ and Ca⁺⁺ [Phe+M]⁺⁺ (M = Be⁺⁺, Mg⁺⁺ and Ca⁺⁺) were studied. The calculated values of metal ion affinity (MIA), BE and the Gibbs free energies of each [Phe+M] ⁺⁺ complexes were found to be in the order of Be⁺⁺ > Mg⁺⁺ > Ca⁺⁺. Among the seven [Phe+M]⁺⁺ complexes, the most stable conformer has charge solvation structure where the metal cations coordinated through tridentate bonds with -N, -O atoms and benzene ring (N/O/Ring). The [Phe+Be]⁺⁺ complex has maximum MIA value, 353.3 kcal/mol than that of [Phe+Mg]⁺⁺ and [Phe + Ca]⁺⁺ complexes. Thus, the complex [Phe+Be]⁺⁺ is energetically more stable than that of [Phe+Mg]⁺⁺ and [Phe + Ca]⁺⁺. The IR spectra of each seven conformers of [Phe+M]⁺⁺ complexes have been also calculated. The wavnumber position of (-CO) stretching mode was used to determine the charge/salt bridge structures of the [Phe+M]⁺⁺ complex. The most stable [Phe+M]⁺⁺ complex has been also verified through the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) analysis.     

Anion and cation binding by a new indole/pyridine/amine-based ion-pair receptor

A new ion-pair receptor bis(3-bromoindol-2-ylmethyl)(2-pyridylmethyl)amine (1) was synthesized and studied for its anion and cation binding behavior using ESI-MS and ¹H NMR spectroscopy. Among halides, 1 exhibits the strongest binding with Cl⁻ to form a 1:1 adduct (K_a = 1042 ± 21 in CD₃CN). Among alkali metal ions, Li⁺ and Na⁺ showed the strongest binding in the formation of a 1·M⁺ complex. The simultaneous binding of Cl⁻ and Li⁺ to 1 was confirmed by ¹H NMR titration of a 1:1 mixture of 1 and Cl⁻ with LiPF₆ in 83:17 v/v mixture of CDCl₃ and DMSO-d₆. DFT-optimized structures of 1·Cl⁻, 1·Li⁺, and 1·Li⁺·Cl⁻ are consistent with the chemical shift changes observed in ¹H NMR studies.     

Solvent extraction of sodium perrhenate by 3m-crown-m ethers (m = 5, 6) and their mono-benzo-derivatives into 1,2-dichloroethane: Elucidation of an overall extraction equilibrium based on component equilibria containing an ion-pair formation in water

Equilibrium constants () for the ion-pair formation of a complex ion NaL⁺ with ReO₄⁻ in water were determined potentiometrically at 25 °C and the ionic strength (I) of 0 mol dm⁻³ using a Na⁺-selective electrode. Here, crown ethers, L, were 15-crown-5 ether (15C5), benzo-15C5, 18-crown-6 ether (18C6) and benzo-18C6. Also, NaReO₄ was extracted by the L into 1,2-dichloroethane and then extraction constants (K_ex/mol⁻² dm⁶) for the species, NaLReO₄, were determined at 25 °C by AAS. These K_ex values were resolved into four component equilibrium constants containing K_MLA calculated at given I values. Based on these data, extraction-abilities of the L against the perrhenate were discussed in comparison with those of sodium picrate-L systems reported previously.     

A near-infrared fluorescent chemodosimeter for silver(I) ion based on an expanded porphyrin

An expanded porphyrin [26]hexaphyrin(1.1.1.1.1.1) was exploited as a fluorescent chemodosimeter for Ag⁺ ions with high sensitivity and selectivity via near-infrared luminescence above 900 nm, a region that is free from optical interference in the visible wavelength range induced by the commonly used matrix and other organic compounds. The association constant for the Ag⁺-porphyrin complexation was evaluated by spectroscopic titration method to be 7.24 × 10¹⁰ M⁻¹.     

A thallium-205 NMR study of thallium acetate ion association in 2,2,2-trifluoroethanol and dimethylsulfoxide

The association of thallium acetate ion in 2,2,2-trifluoroethanol and dimethyl-sulfoxide has been investigated by thallium-205 NMR spectroscopy. Analysis of the association constants as a function of temperature indicates that in trifluoroethanol the association enthalpy and entropy are, respectively, 1.6 kcal-mol^–1 and 19.3 cal-mol^–1-K^–1 and in dimethylsulfoxide they are-0.99 kcal-mol^–1 and 18.0 cal-mol^–1-K^–1. Examination of the temperature dependence of the chemical shift of the ion-pair reveals that in dimethylsulfoxide the ion-pair exists as a contact species, while in trifluoroethanol the solvent-separated ion-pair is more likely.     

Characterization of gem-difluoropropargyl synthons through HF loss from protonated molecules in methane chemical ionization mass spectra

Electron impact and methane chemical ionization mass spectra were obtained following gas chromatography/mass spectrometry for several gem-difluoropropargyl compounds, which had been synthesized as potential intermediates for synthesis of gem-difluoromethylene-containing C-3 acetylenes. EI spectra were variable with respect to the presentation of molecular ions, depending on substituent functional groups present. Methane-CI spectra were characterized by loss of 19 mass units from molecular weight with all compounds examined. These [M − 19]⁺ ions often presented as base peaks of the CI spectra, and were more reliably present and abundant than [M + 1]⁺ ions for these compounds. These ions could have been formed by elimination of HF from the protonated molecules under conditions of methane chemical ionization.     

Vapor-liquid equilibria of ternary systems with 1-ethyl-3-methylimidazolium ethyl sulfate using headspace gas chromatography

Vapor-liquid equilibria (VLE) for two binary systems 1-propanol + water and methyl acetate + methanol, and the ternary mixtures with the ionic liquid 1-ethyl-3-methylimidazolium ethyl sulfate [EMIM]⁺[EtSO₄]⁻ as entrainer were measured by headspace gas chromatography. From the experimental VLE data, the influence of the ionic liquid on the separation factors was investigated. The experimental results for the ternary systems show that [EMIM]⁺[EtSO₄]⁻ has a great influence on the separation factors of the systems investigated. Furthermore, the experimental separation factors were compared with the predicted ones of other ionic liquids and conventional selective solvents using modified UNIFAC (Dortmund).     

Complexation of tetrandrine with calcium ion probed by various spectroscopic methods and molecular modeling

The formation of the complex between tetrandrine and the calcium ion, in solution, was studied using FTIR, UV-Vis, ¹H NMR, ¹³C NMR and electrospray mass spectroscopy spectroscopic methods and molecular modeling. The calcium salts used were: Ca(ClO₄)₂·4H₂O and Ca(Picrate)₂ in the solvents: acetonitrile (CH₃CN), deuterated acetonitrile (CD₃CN) and tetrahydrofurane (THF). The determined complex stability constant was: 20277±67 dm³ mol⁻¹ and corresponding free energy ΔG₀=−5.820±0.002 kcal mol⁻¹. The molecular simulation of the complex formation with the MM3 Augmented force field integrated in CAChe provided useful data about its energy. Combining the experimental results and molecular modeling we propose a model for the structure of tetrandrine-Ca complex with an eight coordinated geometry.     

Selection of entrainers in the 1-hexene/n-hexane system with a limited solubility

Vapor-liquid equilibria (VLE) have been measured for five 1-hexene/n-hexane/ionic liquid systems and 1-hexene/n-hexane/NMP (N-methyl-2-pyrrolidone) system with a headspace-gas chromatography (HSGC) apparatus at 333.15 K. The ionic liquids investigated were 1,3-dimethylimidazolium tetrafluoroborate [C₂MIM]⁺[BF₄]⁻, 1-butyl-3-methylimidazolium tetrafluoroborate [C₄MIM]⁺[BF₄]⁻, 1-methyl-3-octylimidazolium tetrafluoroborate [C₈MIM]⁺[BF₄]⁻, 1,3-dimethylimidazolium dicyanamide [C₂MIM]⁺[N(CN)₂]⁻ and 1-octylquinolinium bis(trifluoromethylsulfonyl)amide [C₈Chin]⁺[BTA]⁻. It was found that at low feeding concentration of 1-hexene and n-hexane, the separation ability of ionic liquids is in the order of [C₂MIM]⁺[BF₄]⁻ > [C₄MIM]⁺[BF₄]⁻ ≈ [C₂MIM]⁺[N(CN)₂]⁻ > [C₈MIM]⁺[BF₄]⁻ > [C₈Chin]⁺[BTA]⁻, which is consistent with the priori prediction of the COSMO-RS (conductor-like screening model for real solvents) model. But at high feeding concentration, the separation ability of ionic liquids is in the order of [C₂MIM]⁺[BF₄]⁻ < [C₄MIM]⁺[BF₄]⁻ ≈ [C₂MIM]⁺[N(CN)₂]⁻ < [C₈MIM]⁺[BF₄]⁻ < [C₈Chin]⁺[BTA]⁻. The liquid demixing effect should be taken into account. The activity coefficients of 1-hexene and n-hexane at infinite dilution calculated with the COSMO-RS model were correlated using the NRTL, Wilson and UNIQUAC model. In this work the predictive results from the COSMO-RS model and UNIFAC model for the 1-hexene/n-hexane and 1-hexene/n-hexane/NMP systems were compared. The UNIFAC model is one of the most important academic contributions by Prof. Jürgen Gmehling.     

Adduct formation in LC-ESI-MS of nonylphenol ethoxylates: mass spectrometrical, theoretical and quantitative analytical aspects

The analysis of nonylphenol ethoxylate (A₉PEO_n) surfactants with LC-ESI-MS was investigated in a detailed study of the formation of different types of adducts. Part of the observations was explained by calculating their relative stabilities using molecular dynamics techniques.Strong differences in adduct formation behaviour were found for different oligomers.Beside the common sodium adducts, surfactant dimer adducts [2 × A₉PEO_1,2 + Na]⁺, adducts including a solvent molecule [A₉PEO_1,2 + MeOH + Na]⁺ and doubly charged adducts [A₉PEO_>11 + 2 × Na]²⁺ were found.Molecular dynamics calculations showed that the A₉PEO_n molecule wraps itself around the complexing sodium ion in a way that negative electronic charges on oxygen have optimum electrostatic interaction with this ion. van der Waals interactions between alkyl chains are of less importance for the stability of these adducts. Both [2 × A₉PEO_2,5 + Na]⁺ dimer and [A₉PEO_2,5 + Na]⁺ monomer adducts turned out to be stable from an energetic point of view with adducts of A₉PEO₅ being more stable than adducts of A₉PEO₂. Only for the monomer adduct the latter is in accordance with experimental observations.Consequences of the formation of several adducts per A₉PEO_n oligomer for the quantitative analysis of environmental samples were evaluated. In clean samples, it was found that the presence of short-chain A₉PEO_1,2 can cause an overestimation of long-chain A₉PEO_>2. In real environmental extracts, other processes like matrix effects have a stronger influence on the quantitative result, and therefore no significant influence of adduct formation processes could be observed. However, inclusion of [A₉PEO_1,2 + MeOH + Na]⁺ adduct signals does improve the detection limits of the two short-chain oligomers.Correct quantitative results are obtained when A₉PEO₁ and A₉PEO₂ are quantified separately, and longer oligomers with a molar calibration followed by correction of the average molar weight of the A₉PEO_>2 in the sample.     

Silver(I) Cation Complexation with 3α,3'α-Bis(pyridine-n-carboxy) Lithocholic Acid 1,2-Ethanediol Diesters (n = 2–4): 1H, 13C and 15N NMR Spectral Studies and Molecular Orbital Calculations

Three isomeric molecular clefts: 3,3'-bis(pyridine-n-carboxy) lithocholic acid 1,2-ethanediol diesters (n = 2–4) 1–3 have been synthesized and their structures ascertained by ¹H, ¹³C NMR and MALDI TOF MS. Their complex formation with Ag⁺-cation (added as AgO₃ SCF₃) have been investigated by means of NMR and molecular orbital calculations. The coordination behaviour of the silver(I) cation is dependent on the isomerism of the pyridine-n-carboxy moiety. In 1 (pyridine-2-carboxylato = picolinato) both NMR and theoretical calculations strongly suggest that the coordination occurs with the lone electron pairs of the pyridine nitrogen and carbonyl oxygen in both of the arms of the molecular cleft separately. In 2 and 3 (pyridine-3-carboxylato = nicotinato and pyridine-4-carboxylato = isonicotinato) where the distance between the pyridine nitrogen and carbonyl oxygen is too large to allow the same type of coordination as in 1, ₃-complexation with the pyridine ring and carbonyl oxygen of the different arms of the molecular cleft simultaneously is suggested by molecular orbital calculations and supported also by NMR. No Ag⁺-cation coordination was observed with the 1,2-ethanediol oxygens in 1–3.