Spherical Anions Research Articles

Coarse-grained simulations of an ionic liquid-based capacitor: II. Asymmetry in ion shape and charge localization

In this work, which is a continuation of part I, we introduce a primitive model for an ionic liquid (IL) that can account for the planar shape of cations typical for ILs like imidazolium. The model consists of a spherical anion and a triangular cation consisting of three spheres, where one or all three vertices of the triangle can carry electric charge. We use molecular dynamics simulations to study the differential capacitance Cd of an ionic liquid confined between two planar electrodes. Our goal is to elucidate the complex dependence of Cd on the electrode potential U in terms of simple entities such as the shape and charge distribution of the ions. For this purpose, we compare the results from the current model to the results based on the models with spherical cations that possess asymmetry in ion valence and shape that were analyzed in detail in part I of this work. We show that the various possible stackings of the triangles near the cathode lead to noticeable new features in Cd(U) as compared to the spherical models. Different distributions of charges on the triangle lead to different preferred orientations of the cations near the cathode that are moreover potential dependent.

Anion-Induced Dimerization in p-Squaramidocalix[4]arene Derivatives

Spherical anions induce the dimerization of calix[4]arene derivatives 3 and 4 bearing squaramide moieties at the exo rim (p-squaramidocalixarenes). (1)H NMR titration experiments showed that unlike the distal isomer 3, proximal p-squaramidocalixarene 4 is also able to form dimeric complexes with trigonal-planar anions.

Bidentate Urea Derivatives of p-tert-Butyldihomooxacalix[4]arene: Neutral Receptors for Anion Complexation

Three new bidentate ureidodihomooxacalix[4]arene derivatives (phenyl 5a, n-propyl 5b, and tert-butyl 5c) were synthesized in four steps from the parent compound p-tert-butyldihomooxacalix[4]arene and obtained in the cone conformation, as shown by NMR studies. The binding ability of these neutral receptors toward spherical, linear, trigonal planar, and tetrahedrical anions was assessed by (1)H NMR and UV-vis titrations. The structures and complexation energies of some complexes were also studied by DFT methods. The data showed that the association constants are strongly dependent on the nature of the substituent (aryl/alkyl) at the urea moiety. In general, for all the receptors, the association constants decrease with decrease of anion basicity. Ph-urea 5a is the best anion receptor, showing the strongest complexation for F(-) (log K(assoc) = 3.10 in CDCl3) and also high binding affinity for the carboxylates AcO(-) and BzO(-). Similar results were obtained by UV-vis studies and were also corroborated by DFT calculations.

Vibrational dephasing of spherical top anions in aqueous solutions

The vibrational dephasing times for spherical top anions in aqueous solutions calculated from in the shape of the isotropic Raman bands of the fully symmetric vibrations of anions, depending on the temperature and the nature of the anion, are analyzed. It is concluded that the dephasing rates for the anions and their temperature dependences can be reasonably explained within the framework of a model that describes the vibrational dephasing of a diatomic molecule interacting with a solvent molecule by using the Morse potential.

Synthesis of a Preorganized Hybrid Macrobicycle with Distinct Amide and Amine Clefts: Tetrahedral versus Spherical Anions Binding Studies

A new C3v symmetric amido-amine hybrid macrobicycle, L is synthesized toward anion recognition in its protonated states. L contains tri-amide and tetra-amine clefts separated by p-phenylene spacers. The solid-state structure of methanol-encapsulated L exhibits an overall cavity length of ~12.0 Å where the amide and amine -NH protons are converged toward the center of the respective cavities. Conformational analysis of L in solution is established by NOESY NMR. Anion binding of [H3L](3+) with spherical (Cl(-), Br(-), I(-)) and tetrahedral (ClO4(-), SO4(2-)) anions are carried out by isothermal titration calorimeter in dimethylsulfoxide. The association of halides with [H3L](3+) is endothermic and entropy driven. However, association of tetrahedral anions is exothermic in nature and both entropy- and enthalpy-driven. The overall association constants show the following order: HSO4(-) > Br(-)> Cl(-) ≈ ClO4(-). Single crystal X-ray structures of ClO4(-) and Br(-) complexes of protonated L show encapsulation of ClO4(-) in the amide cleft of [H2L](2+) (complex 1) and encapsulation of Br(-) in the ammonium cleft of [H3L](3+) (complex 2). Further, preorganization of L toward encapsulation of spherical and tetrahedral anions is established by comparing its amide, amine, and overall cavity dimensions with 1 and 2.

New coumarin–corrole and –porphyrin conjugate multifunctional probes for anionic or cationic interactions: synthesis, spectroscopy, and solid supported studies

Corroles and porphyrins are very promising probes to be used as materials for anion and metal ion detection. Here, we present the synthesis and characterization of two new corrole–coumarin derivatives 7–8 and some porphyrin–coumarin analogs 3–6.The sensing ability of the metalloconjugates was studied in the presence of spherical (F−, Cl−), linear (CN−), and bulky anions (CH3COO−). The porphyrin free-base conjugates were studied with Na+, Ca2+, Zn2+, Cd2+, Pb2+, Fe2+, Ba2+, Cu2+, Ag+, and Hg2+, showing a colorimetric effect (color change from purple to yellow) and an unprecedented selectivity for Hg2+.The insertion of coumarin moiety confers an unusual solubility of these conjugates in ethanol. One of the porphyrin free-base conjugate was fully studied in a mixture EtOH/H2O (50:50) and showed a similar behavior with Hg2+. Under these conditions, the conjugate presented a higher association constant than in toluene and was able to detect and quantify a minimal amount of 0.6 ppm and 1.2 ppm of Hg2+, respectively. Having in mind the biological and environmental application of these conjugates, non-expensive solid supports, like agarose and natural cellulose polymers were developed. In the cellulose support material (filter paper) the colorimetric effect for Hg2+ reveals a similar behavior as in solution.In addition pH studies carried out with the same conjugate showed a green color at low pH and a yellow color at high pH values in solution and in solid supports.

Introducing Charge Hydration Asymmetry in the Realm of Continuum Solvation

Charge hydration asymmetry (CHA) manifests itself in the experimentally observed strong dependence of free energy of ion hydration on the sign of the ion charge. This asymmetry is not consistently accounted for by popular models of solvation; its magnitude varies greatly between the models. While it is clear that CHA is somehow related to charge distribution within a water molecule, the exact nature of this relationship is unknown. We propose a simple, yet general and rigorous criterion that relates rotational and charge inversion properties of a water molecule's charge distribution with its ability to cause CHA. We show which electric multipole components of a water molecule are key to explain its ability for asymmetric charge hydration. We then test several popular water models and explain why specific models show none, little, or strong CHA in simulations. We use the gained insight to derive an analogue of the Born equation that includes the missing physics necessary to account for CHA and does not rely on redefining the continuum dielectric boundary. The proposed formula is as simple as the original, does not contain any fitting parameters, and predicts hydration free energies and entropies of spherical cations and anions within experimental uncertainty. We further incorporate CHA into the framework of Generalized Born continuum solvation model; our findings suggest that the gap between the practical continuum electrostatics framework and the more fundamental explicit solvent treatment can be reduced considerably by explicitly introducing CHA into the existing framework.

Interactions between Keggin Anions in Water: The Higher Their Charge, the Higher Their Condensation? A Simulation Study

AbstractWe report molecular dynamics (MD) simulations of aqueous solutions of Keggin heteropolyacids XWn– nH3O+ (XWn– = [PW12O40]3–, [SiW12O40]4–, and [AlW12O40]5–), the aim of which was to investigate whether the anions increasingly repulse each other in water when their charge increases from –3 to –5. The MD and PMF (potential of mean force) results indicate that this is not the case. All three anions are found to display short XWn–···XWn– contacts (“dimers”), the amount of which increases at increasing concentrations. However, the proportion of dimers follows the sequence SiW4– < PW3– < AlW5–, which is unexpected from interanionic Coulomb forces. The least‐charged anions are mainly attracted by hydrophobic forces, whereas the most charged AlW5– anions afford the highest proportion of dimers through specific interactions with H3O+ counterions. Similar features are observed in two series of fictitious analogues of XWn– (n = 3 to 5): the Sn– spherical anions, and the XWn+ cations (with all atomic charges of XWn– inverted and “H3O–” as counterions). The key role of counterion condensation on the stabilization of the most negatively charged dimers is further demonstrated by comparing Li+ salts to Na+ and Cs+ salts of the different XWn– anions: anion–anion dimerization is found to be highest between AlW5– anions and in the presence of the “hardest” counterions (Li+). Likewise, with Eu3+ multivalent AlW5– counterions condense into a concentrated ionic domain in water. Finally, all three types of XWn– anions are found to adsorb at the aqueous interface with graphite. These findings are important for understanding processes like dimerization, condensation, third phase formation, and the assembly of polyoxometalates and macroions in water or at aqueous interfaces.

C3i-Symmetric Octanuclear Cadmium Cages: Double-Anion-Templated Synthesis, Formation Mechanism, and Properties

A series of C(3i)-symmetric bicapped trigonal antiprismatic Cd(8) cages [2X@Cd(8)L(6)(H(2)O)(6)]⋅n Y⋅solvents (X = Cl(-), Y = NO(3)(-), n = 2: MOCC-4; X = Br(-), Y = NO(3)(-), n = 2: MOCC-5; X = NO(3)(-), Y = NO(3)(-), n = 2: MOCC-6; X = NO(3)(-), Y = BF(4)(-), n = 2: MOCC-7; X = NO(3)(-), Y = ClO(4)(-), n = 2: MOCC-8; X = CO(3)(2-), n = 0: MOCC-9), doubly anion templated by different anions, were solvothermally synthesized by means of a flexible ligand. Interestingly, the CO(3)(2-) template for MOCC-9 was generated in situ by two-step decomposition of DMF solvent. For other MOCCs, spherical or trigonal monovalent anions could also play the role of template in their formation. The template abilities of these anions in the formation of the cages were experimentally studied and are discussed for the first time. Anion exchange of MOCC-8 was carried out and showed anion-size selectivity. All of the cage-like compounds emit strong luminescence at room temperature.

Environmental Influence on the Single-Molecule Magnet Behavior of [MnIII6CrIII]3+: Molecular Symmetry versus Solid-State Effects

The structural, spectroscopic, and magnetic properties of a series of [Mn(III)(6)Cr(III)](3+) (= [{(talen(t-Bu(2)))Mn(III)(3)}(2){Cr(III)(CN)(6)}](3+)) compounds have been investigated by single-crystal X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and electronic absorption spectroscopy, elemental analysis, electro spray ionization-mass spectrometry (ESI-MS) and matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS), cyclic voltammetry, AC and DC magnetic measurements, as well as theoretical analysis. The crystal structures obtained with [Cr(III)(CN)(6)](3-) as a counterion exhibit (quasi-)one-dimensional (1D) chains formed by hydrogen-bonded (1) or covalently linked (2) trications and trianions. The rod-shaped anion lactate enforces a rod packing of the [Mn(III)(6)Cr(III)](3+) complexes in the highly symmetric space group R3[overline] (3) with a collinear arrangement of the molecular S(6) axes. Incorporation of the spherical anion BPh(4)(-) leads to less-symmetric crystal structures (4-6) with noncollinear orientations of the [Mn(III)(6)Cr(III)](3+) complexes, as evidenced by the angle between the approximate molecular C(3) axes taking no specific values in the range of 2°-69°. AC magnetic measurements on freshly isolated crystals (1a and 3a-6a), air-dried crystals (3b-6b), and vacuum-dried powder samples (3c-6c) indicate single-molecule magnet (SMM) behavior for all samples with U(eff) values up to 28 K. The DC magnetic data are analyzed by a full-matrix diagonalization of the appropriate spin-Hamiltonian including isotropic exchange, zero-field splitting, and Zeeman interaction, taking into account the relative orientation of the D-tensors. Simulations for 3a-6a and 3c-6c indicate a weak antiferromagnetic exchange between the Mn(III) ions in the trinuclear subunits (J(Mn-Mn) = -0.70 to -0.85 cm(-1), Ĥ(ex) = -2∑(i<j )J(ij)Ŝ(i)·Ŝ(j)) that is overcome by the stronger antiferromagnetic interaction via the Cr-C≡N-Mn pathway (J(Cr-Mn) = -3.00 to -5.00 cm(-1)), leading to an overall ferrimagnetic coupling scheme with an S(t) = (21)/(2) spin ground state. The differences in U(eff), J(Mn-Mn), and J(Cr-Mn) for the investigated samples are rationalized in terms of subtle variations in the molecular and crystal structures. In particular, a magnetostructural correlation between the Mn-N(C≡N) bond length and the J(Cr-Mn) exchange coupling is inferred from the magnetic measurements and corroborated by DFT calculations. The results of this detailed study on [Mn(III)(6)Cr(III)](3+) allow the formulation of some key recipes for a rational improvement of the SMM behavior.

Charge Hydration Asymmetry: The Basic Principle and How to Use It to Test and Improve Water Models

Charge hydration asymmetry (CHA) manifests itself in the experimentally observed strong dependence of free energy of ion hydration on the sign of the ion charge. This asymmetry is not consistently accounted for by popular models of solvation; its magnitude varies greatly between the models. While it is clear that CHA is somehow related to charge distribution within a water molecule, the exact nature of this relationship is unknown. We propose a simple, yet general and rigorous criterion that relates rotational and charge inversion properties of a water molecule's charge distribution with its ability to cause CHA. We show which electric multipole components of a water molecule are key to explain its ability for asymmetric charge hydration. We then test several popular water models and explain why specific models show none, little, or strong CHA in simulations. We use the gained insight to derive an analogue of the Born equation that includes the missing physics necessary to account for CHA and does not rely on redefining the continuum dielectric boundary. The proposed formula is as simple as the original, does not contain any fitting parameters, and predicts hydration free energies and entropies of spherical cations and anions within experimental uncertainty. Our findings suggest that the gap between the practical continuum electrostatics framework and the more fundamental explicit solvent treatment may be reduced considerably by explicitly introducing CHA into the existing continuum framework.

Designer Ionic Liquid Crystals Based on Congruently Shaped Guanidinium Sulfonates

Ionic liquid crystals are mesogenic compounds that consist of cations and anions, usually rod-like cations and spherical anions. Herein we report a new method for the synthesis of ionic liquid crystals by using cations and anions of the same molecular shape with oppositely charged head groups. Thus, 4-alkoxyphenylpentamethylguanidinium 4-alkoxyphenylsulfonate ion pairs have been synthesised. 4-Alkoxyphenylpentamethylguanidinium iodides were also prepared to determine the influence of congruently shaped anions, in comparison with their spherical counterparts, on mesophase behaviour, which was investigated by differential scanning calorimetry (DSC), polarising optical microscopy (POM) and X-ray diffraction (XRD). All the liquid crystalline salts exhibit smectic A mesophases with strongly interdigitated bilayer structures. The guanidinium sulfonate ion pairs show mesomorphic properties from shorter alkyl chain lengths (≥C(9)) and lower melting points (≈10 K), whereas the corresponding guanidinium iodides are liquid crystalline for longer alkyl chain lengths (≥C(14)). For chains with ≥C(18), however, the mesophase range decreases for the sulfonate ion pairs, but not for the iodide salts.

Quinolinium and isoquinolinium ionic liquid crystals

Ionic liquid crystals based on quinolinium and isoquinolinium salts were prepared by quaternization of quinoline and isoquinoline, respectively. In the first place the influence of the alkyl chain on the thermal behaviour was investigated. Two types of (iso)quinolinium salts were synthesized. Long-chained (iso)quinolinium cations (with chain lengths varying from C12H25 to C22H45), with the inclusion of the odd homologues C17H35 and C19H39, were combined with the spherical anions bromide, tetrafluoroborate (BF4−) and hexafluorophosphate (PF6−). Dodecyl sulfate, dioctyl-, dihexyl- and dicyclohexylsulfosuccinate anions allowed the introduction of anions with (long) alkyl chains. It is shown that a subtle balance between strong electrostatic forces and the degree of disorder originating from molten alkyl chains is crucial for mesophase formation. The influence of the anion size on the mesophase behaviour was studied. Smectic A phases were observed for the long chain analogues of the bromide, tetrafluoroborate and hexafluorophosphate salts. The minimum alkyl chain length needed to induce mesomorphism increases when the bromide is exchanged by more voluminous anions, while the transition temperatures are lowered. The introduction of an alkyl chain in the anionic part drastically changes the thermal behaviour. The dodecyl sulfate salts show smectic A phases for cations with much shorter chain lengths than the other anions. For the dioctylsulfosuccinate salts this trend is even more pronounced, as the N-methyl(iso)quinolinium dioctylsulfosuccinate salts exhibited enantiotropic smectic A phases at ambient temperature. Structural models for the packing of the quinolinium and isoquinolinium salts in the liquid-crystalline state are presented, as well as the crystal structures of N-octylquinolinium dodecyl sulfate and N-octylisoquinolinium bromide.

Anion-Dependent Formation of Helicates versus Mesocates of Triple-Stranded M2L3 (M = Fe2+, Cu2+) Complexes

A series of dinuclear triple-stranded complexes, [Fe(2)L(3)⊃X]X(6) [X = BF(4)(-) (1), ClO(4)(-) (2)], [Fe(2)L(3)⊃SO(4)](2)(SO(4))(5) (3), [Fe(2)L(3)⊃Br](BPh(4))(6) (4), Fe(2)L(3)(NO(3))Br(6) (5), and [Cu(2)L(3)⊃NO(3)](NO(3))(6) (6), which incorporate a central cavity to encapsulate different anions, have been synthesized via the self-assembly of iron(II) or copper(II) salts with the N,N'-bis[5-(2,2'-bipyridyl)methyl]imidazolium bromide (LBr) ligand. X-ray crystallographic studies (for 1-4 and 6) and elemental analyses confirmed the cagelike triple-stranded structure. The anionic guest is bound in the cage and shows remarkable influence on the outcome of the self-assembly process with regard to the configuration at the metal centers. The mesocates (with different configurations at the two metal centers) have formed in the presence of large tetrahedral anions, while helicates (with the same configuration at both metal centers) were obtained when using the relatively smaller spherical or trigonal-planar anions Br(-) or NO(3)(-).

Encapsulation Chalcogen Anions in Perfluorinated Silicon Fullerene: X2−@Si20F20 (X=O, S, Se)

AbstractThe structures and stabilities of cage Si20F20 and its endohedral complexes X2−@Si20F20 (X=O, S, Se) were determined at the B3LYP/6‐31G(d) levels of density functional theory (DFT). It is found that the adiabatic electron affinity (EAad) of host cage Si20F20 (Ih) is higher than that of isolated O atom (4.24 vs. 1.46 eV). This suggests the Si20F20 cage can selectively trap and stabilize the capsulated spherical anions. The calculations predict that X=S and Se are nearly located at the center of the cage, and O dramatically deviates from the center in C3v symmetry. Moreover, the corresponding X2−@Si20F20 complexes have more negative inclusion energies (ΔEinc) and thermodynamic parameters (ΔZ) than X2−@C20F20. The amount of charge that is being transferred from the encapsulated anions to the cage increases with the atomic radius, i.e., from O2− (ca. 45%), S2− (ca. 51%) to Se2− (ca. 59%), and such a novel model of cage may have practical uses as potential and electrical building units of nanoscale materials.

Anion Binding in the C3v-Symmetric Cavity of a Protonated Tripodal Amine Receptor: Potentiometric and Single Crystal X-ray Studies

Tris(2-aminoethyl)amine (tren) based pentafluorophenyl-substituted tripodal L, tris[[(2,3,4,5,6-pentafluorobenzyl)amino]ethyl]amine receptor is synthesized in good yield and characterized by single crystal X-ray diffraction analysis. Detailed structural aspects of binding of different anionic guests toward L in its triprotonated form are examined thoroughly. Crystallographic results show binding of fluoride in the C(3v)-symmetric cavity of [H(3)L](3+) where spherical anion fluoride is in tricoordinated geometry via (N-H)(+)···F interaction in the complex [H(3)L(F)]·[F](2)·2H(2)O, (3). In the case of complexes [H(3)L(OTs)]·[OTs](2), (4) and [H(3)L(OTs)]·[NO(3)]·[OTs], (5), tetrahedral p-toluenesulphonate ion is engulfed in the cavity of [H(3)L](3+) via (N-H)(+)···O interactions. Interestingly, complex [(H(3)L)(2)(SiF(6))]·[BF(4)](4)·CH(3)OH·H(2)O, (6) shows encapsulation of octahedral hexafluorosilicate in the dimeric capsular assembly of two [H(3)L](3+) units, via a number of (N-H)(+)···F interactions. The kinetic parameters of L upon binding with different anions are evaluated using a potentiometric study in solution state. The potentiometric titration experiments in a polar protic methanol/water (1:1 v/v) binary solvent system show high affinity of the receptor toward more basic fluoride and acetate anions, with a lesser affinity for other inorganic anions (e.g., chloride, bromide, nitrate, sulfate, dihydrogenphosphate, and p-toluenesulphonate).

Purification of lactic acid from fermentation broth by spherical anion exchange polymer

AbstractLactic acid, as a versatile chemical, was purified from fermentation broth by solid phase extraction with a spherical porous poly(4‐vinylpyridine). Adsorption isotherm of lactic acid on poly(4‐vinylpyridine) was first investigated with model solutions. The factors which affect the performance of separation and purification were then investigated. The obtained results indicate that the sorbent had a high adsorption capability of lactic acid, of which the maximum adsorbed lactic acid was 180.0 mg g−1. Under the optimal condition the lactic acid was purified from fermentation broth by solid phase extraction with the purity of 88% and recovery yield of 95%. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

ChemInform Abstract: Anion Recognition by Hydrogen Bonding: Urea‐Based Receptors

AbstractReview: ca. 100 refs.

ChemInform Abstract: Anion Binding in Covalent and Self‐Assembled Molecular Capsules

AbstractReview: 149 refs.

Anion–π Interactions in Salts with Polyhalide Anions: Trapping of I42−

The directionality of interaction of electron-deficient π systems with spherical anions (e.g,. halides) can be controlled by secondary effects like NH or CH hydrogen bonding. In this study a series of pentafluorophenyl-substituted salts with polyhalide anions is investigated. The compounds are obtained by aerobic oxidation of the corresponding halide upon crystallization. Solid-state structures reveal that in bromide 2, directing NH-anion interactions position the bromide ion in an η(1)-type fashion over but not in the center of the aromatic ring. The same directing forces are effective in corresponding tribromide salt 3. In the crystal, the bromide ion is paneled by four electron-deficient aromatic ring systems. In addition, compounds 4 and 6, which have triiodide and the rare tetraiodide dianion as anions, are described. Computational studies reveal that the latter is highly unstable. In the present case it is stabilized by the crystal lattice, for example, by interaction with electron-deficient π systems.