Anion Solvation Research Articles

Recognition and sensing of AcO− and F− using a calix[4]pyrrole-derived hydrazone: a potential molecular keypad lock

Calix[4]pyrroles based colorimetric anion receptor 2 could recognize F− and AcO− anions in DMSO solvent. This type of sensing behaviour could mimic a molecular level keypad lock stimulated by the two sequential chemical inputs (AcO− and F−), which has the potential for application in security devices.

Zero-point energy effects in anion solvation shells

By comparing classical and quantum-mechanical (path-integral-based) molecular simulations of solvated halide anions X(-) [X = F, Cl, Br and I], we identify an ion-specific quantum contribution to anion-water hydrogen-bond dynamics; this effect has not been identified in previous simulation studies. For anions such as fluoride, which strongly bind water molecules in the first solvation shell, quantum simulations exhibit hydrogen-bond dynamics nearly 40% faster than the corresponding classical results, whereas those anions which form a weakly bound solvation shell, such as iodide, exhibit a quantum effect of around 10%. This observation can be rationalized by considering the different zero-point energy (ZPE) of the water vibrational modes in the first solvation shell; for strongly binding anions, the ZPE of bound water molecules is larger, giving rise to faster dynamics in quantum simulations. These results are consistent with experimental investigations of anion-bound water vibrational and reorientational motion.

Silver(i) supramolecular complexes generated from isophorone-based ligands: crystal structures and enhanced nonlinear optical properties through metal complexation

By self-assembly of (E)-2-(3-(4-(1H-imidazol-1-yl)styryl)-5,5-dimethylcyclohex-2-enylidene)malononitrile (L(1)) and (E)-2-(3-(4-(1H-1,2,4-triazol-1-yl)styryl)-5,5-dimethylcyclohex-2-enylidene)malononitrile (L(2)) with silver(I) salts, eight new complexes, namely AgL(1)2ClO4 (1), AgL(1)2NO3 (2), [AgL(1)2NO3]·C6H6 (3), [AgL(1)2OOCCF3]·C6H6 (4), [AgL(1)2PF6]·C6H6 (5), AgL(2)2NO3 (6), [AgL(2)OOCCF3]2 (7) and AgL(2)2PF6 (8), are presented along with an analysis of their structural features. The structures are built up through the combination of coordination bonds, Ag···π, Ag···F (or O), hydrogen bonding, and π···π stacking interactions to generate new supramolecular architectures. We observed the formation of two-dimensional coordination polymers for complex 7. Solvent benzene molecules and anions are dispersed in the supramolecular structure and play a vital role in building the supramolecular structures of the complexes. The nonlinear optical (NLO) properties of the complexes were investigated using the Z-scan technique and complexes 1, 2, 3, 4 and 7 show obviously nonlinear absorption compared with ligands (L(1) and L(2)).

Picosecond Pulse Radiolysis Study of Dynamics of Solvation of Electron and Fluorenone Anion in Primary Alcohols

We have studied the dynamics of solvation of electron injected directly into primary alcohols as well as that of fluorenone anion using pulse radiolysis technique with the time resolution of about 15 ps. Unlike in the previous reports, we observe nonexponential dynamics of both electron and anion solvation. While the ultrafast component, τ1 (<15 ps) representing the inertial time scale of the dynamics is faster than the time resolution of the spectrometer, the slower component, τ2, has been assigned to the translational motion leading to structural changes of the hydrogen bonding network of the solvent in the inner solvation cell or alcohol cluster. τ2 agrees well with the electron solvation times reported by the earlier authors. τ3 is associated with the restructuring of the hydrogen bond network structure of the solvent in the region outside the solvation cell. Nonexponential solvation dynamics of the fluorenone anion has been described well by a two-component process. The most important observation in this work is that the lifetime of the shorter component, τ1, determined in four alcoholic solvents, is much longer than the electron solvation time in the corresponding solvents determined in this work or anion solvation time reported earlier. The lifetime of this component is nearly comparable with the average dipolar solvation time but shorter than the longitudinal relaxation time of the solvent. In the case of anion, τ1 has been assigned to the restructuring of the first solvation shell by breakage of solvent hydrogen bonds of the fluorenone molecule and formation of hydrogen bonds with the anion. In this case, too, the longer component, τ2, with the lifetime of a few nanoseconds, has been assigned to reorganization of hydrogen bonds in the solvent hydrogen bond network structure.

Electron-induced dissociation of chlorosilanes: Role of aromatic side groups in gas phase and solution chemistry

Dissociative electron attachment (DEA) to chlorotrimethylsilane (Me3SiCl) and chlorodimethylphenylsilane (PhMe2SiCl) was studied to reveal a possible enhancing effect of the aromatic side group on the SiCl bond dissociation. Calculations point to a relevant interaction between the lowest unoccupied π* orbital of the phenyl ring and the σ*(SiCl) orbital and a consequent lowering of the lowest-energy electron attachment channel. It was previously reported that such a situation can lead to a significant enhancement of DEA. However, the lowest energy DEA channel in the investigated chlorosilanes lies below the thermodynamic limit for dissociation of the SiCl bond in the radical anion and thus cannot contribute to the Cl− yield. In consequence, release of chloride ions is in fact the dominant fragmentation channel but the Cl− yield is not noticeably enhanced in PhMe2SiCl. In contrast to the DEA results, comparative experiments on the reductive coupling in THF of Me3SiCl, PhMe2SiCl, and benzyldimethylchlorosilane (BzMe2SiCl) under identical conditions reveal a significant enhancement of the reactivity by aromatic side groups. As this finding does not correlate with the DEA results, an alternative explanation for the different reactivity of Me3SiCl and PhMe2SiCl in solution is suggested based on their vertical electron attachment energies and considering the impact of these quantities on the equilibrium between solvated electrons and neutral reactants on one side and the solvated radical anion on the other.

Coordination of Terpyridine to Li+ in Two Different Ionic Liquids

On the basis of (7)Li NMR experiments, the complex-formation reaction between Li(+) and the tridentate N-donor ligand terpyridine was studied in the ionic liquids [emim][NTf2] and [emim][ClO4] as solvents. For both ionic liquids, the NMR data implicate the formation of [Li(terpy)2](+). Density functional theory calculations show that partial coordination of terpyridine involving the coordination of a solvent anion can be excluded. In contrast to the studies in solution, X-ray diffraction measurements led to completely different results. In the case of [emim][NTf2], the polymeric lithium species [Li(terpy)(NTf2)]n was found to control the stacking of this complex, whereas crystals grown from [emim][ClO4] exhibit the discrete dimeric species [Li(terpy)(ClO4)]2. However, both structures indicate that each lithium ion is formally coordinated by one terpy molecule and one solvent anion in the solid state, suggesting that charge neutralization and π stacking mainly control the crystallization process.

Synthesis, structure and supramolecular features of cobalt(III) and cobalt(II) complexes, [CoHxL](ClO4)y (x = y = 3, 2, 1.50, 1.45, 1 and 0 and x = 3, y = 2) of a triprotic imidazole containing Schiff base ligand. Effect of protonation state on supramolecular structure

Aerial reaction of cobalt(II) perchlorate with H3(1) {H3(1) is the tripodal ligand derived from the condensation of tris(2-aminoethyl)amine with three equivalents of 4-methyl-5-imidazolecarboxaldehyde} in acidic methanol results in isolation of both the orange [CoH3(1)](ClO4)2 (trace) and red [CoH3(1)](ClO4)3 (2 pseudopolymorphs). An analogous reaction in methanol gives [CoH2(1)](ClO4)2. Reaction of [CoH2(1)](ClO4)2 (generated in situ) with aqueous sodium hydroxide gives [CoH(1)](ClO4) (two pseudopolymorphs) and a trace amount of [CoH1.45(1)](ClO4)1.45. Reaction of [CoH3(1)](ClO4)3 with 1.5 equivalents of hydroxide gives [CoH1.5(1)](ClO4)1.5. Reaction of [CoH(1)](ClO4) with methanolic potassium hydroxide in acetonitrile gave [Co(1)] (two pseudopolymorphs). Complexes were characterized by EA and IR if available in sufficient amounts. All ten complexes were structurally characterized and their metrical parameters are consistent with a high spin cobalt(II) for [CoH3(1)](ClO4)2 and low spin cobalt(III) for all of the cobalt(III) complexes. [CoH3(1)](ClO4)2 and one polymorph of [CoH3(1)](ClO4)3 dimerize by hydrogen bonding through three perchlorate anions. [CoH2(1)](ClO4)2 and one of the pseudopolymorphs of [CoH(1)](ClO4) form intermolecular imidazole-H…imidazolate hydrogen bonds resulting in hetero and homochiral 1D zig-zag chains, respectively. [CoH1.5(1)](ClO4)1.5 forms a tetrahedral array of octahedral cobalt complexes held together by intermolecular imidazole-H…imidazolate hydrogen bonds. [CoH1.45(1)](ClO4)1.45 forms a hexameric structure with a large central channel containing solvent and perchlorate anions. [CoH(1)](ClO4) and both polymorphs of [Co(1)] form no intermolecular imidazole-H…imidazolate hydrogen bonds but do exhibit extensive hydrogen bond formation with water.

A quantum molecular dynamics study of aqueous solvation dynamics

Ring polymer molecular dynamics experiments have been carried out to examine effects derived from nuclear quantum fluctuations at ambient conditions on equilibrium and non-equilibrium dynamical characteristics of charge solvation by a popular simple, rigid, water model, SPC/E , and for a more recent, and flexible, q-TIP4P/F model, to examine the generality of conclusions. In particular, we have recorded the relaxation of the solvent energy gap following instantaneous, ±e charge jumps in an initially uncharged Lennard-Jones-like solute. In both charge cases, quantum effects are reflected in sharper decays at the initial stages of the relaxation, which produce up to a ∼20% reduction in the characteristic timescales describing the solvation processes. For anionic solvation, the magnitude of polarization fluctuations controlling the extent of the water proton localization in the first solvation shell is somewhat more marked than for cations, bringing the quantum solvation process closer to the classical case. Effects on the solvation response from the explicit incorporation of flexibility in the water Hamiltonian are also examined. Predictions from linear response theories for the overall relaxation profile and for the corresponding characteristic timescales are reasonably accurate for the solvation of cations, whereas we find that they are much less satisfactory for the anionic case.

First-Principles Molecular Dynamics Simulation of Atmospherically Relevant Anion Solvation in Supercooled Water Droplet

We present a comprehensive first-principles Born-Oppenheimer molecular dynamics (BOMD) simulation study of halide anion solvation in a deeply supercooled water droplet (with diameter ∼1.8 nm). We show that larger halide anions Br(-) and I(-) show "outer-layer surface preference", whereas F(-) exhibits bulk preference. Contrary to behavior of other halide anions, Cl(-) in the water droplet appears to exhibit no strong tendency of surface or bulk preference at either the supercooled or ambient condition, a phenomenon not previously reported in the literature. BOMD simulation indicates that fully hydrated complex of F(-) is mainly five-fold coordinated (showing square pyramid structure), whereas Cl(-), Br(-) and I(-) hydrated complexes are either five- or six-fold coordinated (showing sandwich-like structure). Among Cl(-), Br(-) and I(-) anions, BOMD simulation indicates that I(-) exhibits the largest diffusion coefficient despite its largest size. However, computed resident time of the four halide ions suggests that Br(-) can approach from the interior to the surface of the water droplet at a much faster rate than I(-) and Cl(-).

Coexistence of molecular Pd6 triangle and Pd8 square self-assembled from naphthyl-dipyrazole with di-palladium motifs

Two novel nanosized bipyrazolate-bridged metallo-macrocycles with dipalladium(II,II) corners, {[(bpy)Pd]8L4}(NO3)8 and {[(bpy)Pd]6L3}(NO3)6 [L = 1, 4-di(3′,5′-dimethyl-1H-pyrazolyl-4yl)naphthalene] have been synthesized through a directed self-assembly approach that involves spontaneous deprotonation of the 1H-bipyrazolyl ligand in aqueous solution. These crown-shaped complexes with deep cavities potentially served as the host to solvent molecules and anions. Such metallo-macrocyclic structures have been characterized by single-crystal X-ray diffraction analysis, elemental analysis, 1H and 13CNMR, high resolution electrospray ionization mass spectrometry, UV–visible spectroscopy, and luminescence spectroscopy.

An Ion’s Perspective on the Molecular Motions of Nanoconfined Water: A Two-Dimensional Infrared Spectroscopy Study

The vibrational population relaxation and hydration shell dynamics of the symmetric tricyanomethanide (TCM) anion are investigated in a sodium bis(2-ethylhexyl)sulfosuccinate reverse micelle as a function of the water pool radius. Two-dimensional infrared (IR) spectroscopy in combination with linear absorption and ultrafast IR pump-probe spectroscopy is utilized in this study. Spectroscopic measurements show that the anion has two bands in the 2160-2175 cm(-1) region, each with its own spectroscopic signatures. Analysis of the vibrational dynamics shows that the two vibrational bands are consistent with the anion located either at the interface or in the water pool. The sensitivity of the TCM anion to the environment allows us to unequivocally monitor the vibrational and hydration dynamics of the anion in those two different environments. A TCM anion located at the interface does not show any significant variation of the vibrational dynamics with the water pool size. On the contrary, the TCM anion inside the water pool exhibits a large and nonlinear variation of the vibrational lifetime and the frequency-frequency correlation time with the pool radius. Moreover, for the solvated anion in water pools of 49 Å in radius (W0 = 30), the vibrational lifetime reaches the values observed for the anion in bulk water while the frequency-frequency correlation time shows a characteristic time higher than that observed in the bulk. In addition, for the first time a model is developed and used to explain the observed nonlinear variation of the spectroscopic observables with the pool size. This model attributes the changes in the vibrational dynamics of the TCM anion in the water pool to the slow and radius-dependent water dynamics present in the confined environment of a reverse micelle.

Substituent effects on the formation and nucleophile selectivity of ring‐substituted phenonium ions in aqueous solution

The reaction of 2-(4-methyphenyl)ethyl tosylate (Me-1-OTs) in 50/50 (v/v) trifluoroethanol/water at 25 °C is first-order in the concentration of azide anion nucleophile. A carbon-13 NMR analysis of the products of the reactions of Me-1-[α-13C]OTs in 50/50 (v/v) trifluoroethanol/water at 25 °C shows the formation of Me-1-[β-13C]OH, Me-1-[β-13C]OCH2CF3 and Me-1-[β-13C]N3 from the trapping of a symmetrical 4-methylphenonium ion reaction intermediate Me-2+. The formation of Me-1-[α-13C]N3 by concerted bimolecular displacement of azide ion at Me-1-[α-13C]OTs (kN = 3.8 × 10-6 M-1 s-1) and of Me-1-[α-13C]OH and Me-1-[α-13C]OCH2CF3 by concerted bimolecular displacement of solvent (ksolv = 1.8 × 10-8 s-1) is also observed. An analysis of the rate and product data provides a value of kaz/ks = 32 M-1 for partitioning of Me-2+ between addition of azide ion and solvent that is nearly 3-fold smaller than kaz/ks = 83 M-1 reported in an earlier study on the partitioning of MeO-2+ [J. Org. Chem.2011, 76, 9568]. This change is attributed to a decrease in nucleophile selectivity with increasing electrophile reactivity for the activation-limited addition of solvent and azide anion to X-2+. These data set a limit of 1/ks ≥ 10-7 s for the lifetime of Me-2+ in aqueous solution.

Salty Glycerol versus Salty Water Surface Organization: Bromide and Iodide Surface Propensities

Salty NaBr and NaI glycerol solution interfaces are examined in the OH stretching region using broadband vibrational sum frequency generation (VSFG) spectroscopy. Raman and infrared (IR) spectroscopy are used to further understand the VSFG spectroscopic signature. The VSFG spectra of salty glycerol solutions reveal that bromide and iodide anions perturb the interfacial glycerol organization in a manner similar as that found in aqueous halide salt solutions, thus confirming the presence of bromide and iodide anions at the glycerol surface. Surface tension measurements are consistent with the surface propensity suggested by the VSFG data and also show that the surface excess increases with increasing salt concentration, similar to that of water. In addition, iodide is shown to have more surface prevalence than bromide, as has also been determined from aqueous solutions. These results suggest that glycerol behaves similarly to water with respect to surface activity and solvation of halide anions at its air/liquid interface.

Communication: Electronic structure of the solvated chloride anion from first principles molecular dynamics

We present first principles molecular dynamics simulations of the chloride anion in liquid water performed using gradient-corrected and hybrid density functionals. We show that it is necessary to use hybrid functionals both for the generation of molecular dynamics trajectories and for the calculation of electronic states in order to obtain a qualitatively correct description of the electronic properties of the solution. In particular, it is only with hybrid functionals that the highest occupied molecular orbital of the anion is found above the valence band maximum of water, consistent with photoelectron detachment measurements. Similar results were obtained using many body perturbation theory within the G0W0 approximation.

Effects of temperature on micellar-assisted bimolecular reaction of methylnaphtalene-2-sulphonate with bromide and chloride ions

Reactivity of methyl naphthalene-2-sulphonate, MeONs, with H2O, Br− and Cl− in water and in cationic micelles of cetyltrialkylammonium surfactants, n-C16H33N+R3X−, R=Me (CTA+), n-Pr (CTPA+), X=Br, Cl, CH3SO3, has been investigated in the temperature range 25–45°C. Micellar rate effects were analysed by using the pseudophase treatment, and the second-order rate constants in the micellar pseudophase were evaluated at the various temperatures. Values of these rate constants increase with temperature, and the effect is less important in micelles than in water and more important for chloride than for bromide ions. Micelles lead to an ion behaviour discrimination, whose extent depends on surfactant type and on temperature, with maximum effect in CTPA+ at 25°C and with bromide being always more reactive than chloride.Quantitative analysis of the temperature effect by the Eyring equation showed that micelles speed up reaction of MeONs with halide ions by decreasing the activation enthalpies, which is partially offset by decreases in the activation entropies. The rate acceleration by increase in surfactant head group size has only enthalpic origin for bromide and only entropic origin for chloride: this different behaviour was rationalised taking into account both solvation of anions and the hydrophobic effect.

Competitive Aryl–Fluorine and Aryl–Halogen (Halogen = Cl, Br) Bond Cleavage with Iridium Porphyrin Complexes

Base-promoted competitive Ar–F and Ar–X (X = Cl, Br) bond cleavage with iridium porphyrin complexes was investigated. Mechanistic studies suggested that Ir(ttp)− (ttp = 5,10,15,20-tetra-p-tolylporphyrinato dianion) cleaves the Ar–F bond via nucleophilic aromatic substitution and Ir2(ttp)2 cleaves the Ar–X (X = Cl, Br) bond via metalloradical ipso substitution. Therefore, a stronger base, polar solvent, lower temperature, and iridium anion precursor favor Ar–F bond cleavage, while a weaker base, nonpolar solvent, higher temperature, and Ir2(ttp)2 precursor favor Ar–X (X = Cl, Br) bond cleavage.

The Performance of Density Functionals for Sulfate-Water Clusters.

The performance of 24 density functionals, Hartree-Fock, and MP2 is assessed with respect to the CCSD(T)/CBS* energetics of 49 sulfate-water clusters with three to six water molecules. Included among the density functionals are GGA, meta-GGA, hybrid GGA, hybrid meta-GGA, and double hybrid density functionals, as well as the LDA. Three types of dispersion corrections (VV10, XDM, and -D) are tested in conjunction with these functionals. The 26 methods are compared using the relative and binding energies of the sulfate-water clusters as the main criteria. It was discovered that a majority of the tested density functionals are unable to simultaneously capture the physics necessary to describe both the relative and binding energies of the anionic solvation clusters. The three density functionals with the best overall performance are XYG3, ωB97X-2, and XYGJ-OS. The only other density functional that performs comparably to these three double hybrids is M11. A majority of the density functionals that contain a fraction of exact exchange tend to perform well only for the relative energies, while functionals lacking exact exchange generally perform poorly with respect to both criteria. However, the meta-GGA functional, M11-L, stands out due to its superior performance for the relative energies. While dispersion correction functionals cannot replace the accuracy provided by MP2 correlation, it is shown that the proper combination of a hybrid GGA functional (LC-ωPBE) with a dispersion correction functional (VV10) can lead to drastic improvements in the binding energies of the parent functional, while preserving its performance with respect to the relative energies. Ultimately, however, MP2 has the best overall performance out of the 26 benchmarked methods.

From solvated ions to ion-pairing: a THz study of lanthanum(iii) hydration

Ion radius and charge density are important parameters that determine the solvation behavior in aqueous electrolyte solutions. Here, we report on high precision THz absorption measurements of solvated LaCl3 and LaBr3 using narrow-band (75-90 cm(-1)) p-Ge laser and wideband (30-350 cm(-1)) Fourier transform spectroscopy. The concentration dependent absorption up to 3.3 M shows a prominent nonlinearity indicating ion pair formation with increasing electrolyte concentration. A more detailed analysis in terms of a chemical equilibrium model allowed us to separate the ion and ion pair contributions from bulk and solvation water. Thus we were able to characterize anion and cation solvation independently. The center frequencies of the Cl(-) and Br(-) rattling modes are in agreement with those found in aqueous alkali and earth alkali halide solutions. The coupling between anion and cation hydration is found to be small. Based upon our detailed analysis we propose increasing formation of solvent shared ion pairs with increasing solute concentration. The well defined ion resonances imply that in spite of its high charge density La(3+) acts locally on the water structure. Terahertz absorption spectroscopy is found here to be an experimental tool which allows us to directly observe solute hydration shells as well as ion pair formation.

Polymerization of methyl methacrylate by latent pre-catalysts based on CO2-protected N-heterocyclic carbenes

Various carbon dioxide-protected N-heterocyclic carbenes (NHCs) have been investigated with regard to their ability to act as thermally latent initiators for the polymerization of methyl methacrylate (MMA). Such CO2-protected NHCs, while completely inactive at room temperature, deliver poly(methyl methacrylate) (PMMA) in high yields upon heating and thus represent truly latent pre-catalysts. Polymerizations were conducted in the bulk, semi-bulk and in solution. Especially tetrahydropyrimidinium-2-carboxylates as well as 1,3-di(tert-butyl)imidazolium-2-carboxylate, both in combination with dimethylsulfoxide (DMSO), were identified as suitable pre-catalysts for the polymerization of MMA. With 1,3-di(tert-butyl)imidazolium-2-carboxylate in toluene, polydispersity indices (PDIs) as low as 1.3 and number-average molecular weights (Mn) of 500 000 g mol−1 could be realized. Tetrahydropyrimidinium-2-carboxylates in conjunction with DMSO resulted in lower molecular weights. Notably, isolated polymer yields up to 96% were possible in some cases, though yields proved to be sensitive to the structure of the initiators used. In principle, at least two different polymerization mechanisms are active. In the presence of DMF or DMSO, the formation of a solvent anion (e.g., DMSO−), which then reacts with the monomer, is proposed. What follows is that only highly basic NHCs work well under these conditions. In contrast, the polymerization of MMA in toluene or in the bulk is probably governed by the nucleophilicity of the NHC, rendering unsaturated, less basic NHCs more applicable. Both mechanisms are discussed.

Halogen Bonding between Anions and Iodoperfluoroorganics: Solution‐Phase Thermodynamics and Multidentate‐Receptor Design

The interactions of iodoperfluoroarenes and -alkanes with anions in organic solvent were studied. The data indicates that favorable halogen-bonding interactions exist between halide anions and the monodentate model compounds C(6)F(5)I and C(8)F(17)I. These data served as a basis for the development of preorganized multidentate receptors capable of high-affinity anion recognition. Several new receptor architectures were prepared, and the multidentate-iodoperfluorobenzoate-ester design, as described in a preliminary communication, was evaluated in more detail. Computation was employed to better interpret the structure-activity relationships arising from these studies. Investigations of the thermodynamics of anion binding (by van't Hoff analysis) and solvent effects reveal details of these halogen bonding interactions.