Types Of Ion Pairs Research Articles

Beyond the Diffusion Limit: Pre-Associated Ion-Pair Photoinitiating Systems for Radical Photopolymerization.

The pre-association mechanism of an ion-pair Type II photoinitiating system (PIS) acting in the visible range was studied. The choice of a dye as photoinitiator (crystal violet) with an excited state lifetime of 200 ps ensured the absence of dynamical quenching by the borate salts used as coinitiators. In spite of the fact that no diffusional bimolecular quenching can take place, excellent polymerization efficiency was found, underlining the high reactivity of the PIS. A saturation effect is observed when increasing the concentration of borate as a consequence of the pre-association mechanism arising from coulombic interaction between the cationic dye and the anionic coinitiator. The association equilibria of the system were described and the corresponding association constant values were calculated, allowing to quantify the pre-association efficiency. This was further successfully correlated to the observed maximal rates of polymerization. The efficiency of this super-stoichiometric sample with an excess of borate was finally compared to the stoichiometric 1:1 dye:borate ion-pair. It is shown that the pre-association mechanism could lead to much higher efficiency than the stoichiometric ion-pair.

An Efficient and Cost-effective Modified Carbon Paste Electrodes for Diltiazem Hydrochloride Determination in Tablets

Background and Objective: This study presented new sensitive and selective modified carbon paste (MCPE) potentiometric sensors modified with different ion pairs for the determination of the antihypertensive drug diltiazem hydrochloride (DTM-HCl) in biological fluids, pharmaceutical preparations, and in its pure form. Methods: Plasticizers, ion pair type, ion pair content, response time, temperature, and pH were just a few of the experimental factors evaluated that were found to affect electrode efficiency. The two electrodes that show the best sensitivity were prepared by mixing diltiazem-tetraphenyl borate (DTM-TPB) ion pair, graphite, and TCP or o-NPOE as a plasticizer. Result: Over the concentration ranges of 1.0x10-5–1.0x10-2, the produced electrodes I and II demonstrated monovalent Nernstian responses of 55.7±0.902 and 57.6±0.451 mV decade-1. The selectivity property of the suggested electrodes was used to study the interference ions. The concentration of DTM-HCl in pharmaceutical formulations and biological fluids was measured using these modified electrodes. During the validation procedure, metrics like linearity, accuracy, precision, limit of detection, limit of quantification, and specificity were used. Conclusion: The obtained results showed good agreement with the HPLC technique as indicated by the F and t-test values and can conclude the possibility of using this potentiometric method in the routine analysis of DTM-HCl.

The role of anions for phosphoric acid uptake behaviors and electrochemical performance of ion-pair type high-temperature polymer electrolyte membranes

Quaternized ion-pair membranes have high phosphoric acid (PA) uptake and retention due to strong interaction energy between quaternary ammonium with PA. However, there is currently a lack of clear understanding of the role of anions on the PA uptake behaviors and mechanism of ion-pair type membranes. In this work, the PA uptake behaviors of quaternized poly (terphenyl piperidinium) (QAPTP-X, X represents anions) with four kinds of anions (Cl−, OH−, HCO3− and H2PO4−) were investigated. Due to the neutralization reaction between PA and OH−/HCO3−, QAPTP-OH− and QAPTP-HCO3− membranes show a faster PA adsorption rate (PA uptake for 2 min: 116 wt% of QAPTP-OH−≈109 wt% of QAPTP-HCO3− >95 wt% of QAPTP-H2PO4− ≫64 wt% of QAPTP-Cl−). Besides, the Pt catalyst is poisoned by strong adsorption anions Cl− migrated from the QAPTP-Cl− membrane, which leads to sluggish electrode reaction kinetics and lower peak density. Therefore, a new perspective is provided for studying the mechanism of PA uptake and electrochemical performance for ion-pair type membranes.

ION PAIR CONVERSION THERMODYNAMICS IN HYDROGEN BROMIDE ALCOHOL SOLUTIONS

The thermodynamic quantities of dissociation of contact and solvent-separated ion pairs into ions, conversion of contact ion pairs into solvent-separated ion pairs of HBr ionogen in n-alcohols from methyl to n-octyl have been calculated by the procedure we set forth earlier for the HCl – n-alcohol systems in the same solvents at 278.15–328.15 K. The following regularities were established in this work: a) positive values of ΔdisGº of contact and solvent-separated ion pairs increase with increasing temperature, the number of carbon atoms in the n-alcohol molecule, and decreasing radius of halide ion, and their sign and magnitude are determined by the entropic component (–TΔdis Sº). In this case, the values of ΔdisGº of contact ion pairs exceed the same values for solvent-separated ion pairs; b) ΔconvGº values for HCl and HBr are also positive, except for ΔconvGº values in methanol at 278.15–328.15 K and HBr solutions at the same temperatures in ethanol. For these cases, by contrast, ΔdisGº(RIP) > ΔdisGº(CIP) and ΔconvGº are negative. As the temperature and radius of the halide ion increase, ΔconvGº become more negative, and vice versa as the hydrocarbon radical increases; c) the concentration of contact ion pairs increases in the methanol-n-octanol series, decreases slightly with increasing temperature and anion radius, and changes within ~30 % (methanol) to 95 % (n-octanol) at 278.15 K. In methanol, solvent-separated ion pairs predominate; in ethanol, the concentration of both types of ion pairs is approximately the same; in other n-octanols, contact ion pairs predominate.

DFT Treatment of Hydrazine - Nitroform Interaction

In the present study, interaction of hydrazine and nitroform (trinitromethane) has been investigated via some models within the constraints of density functional theory at the level of B3LYP/6-311++G(d,p). The data have revealed that the electronic stability order of the models is 3>1>2>5>4 where model-3 is a cyclic one. The others are acyclic and some of them are ion-pair models. Some geometrical, physico chemical and quantum chemical data have been obtained and discussed. The results, overall, indicate that the interaction between the hydrazine and nitroform in the salt form is not ion-pair type, but the hydrogen of nitroform prefers to be linked to carbon atom, thus some sort of nonbonding interactions occur.

Structures of (NaSCN)2(H2O)n -/0 (n = 0-7) and solvation induced ion pair separation: Gas phase anion photoelectron spectroscopy and theoretical calculations.

We studied (NaSCN)2(H2O)n - clusters in the gas phase using size-selected anion photoelectron spectroscopy. The photoelectron spectra and vertical detachment energies of (NaSCN)2(H2O)n - (n = 0-5) were obtained in the experiment. The structures of (NaSCN)2(H2O)n -/0 up to n = 7 were investigated with density functional theory calculations. Two series of peaks are observed in the spectra, indicating that two types of structures coexist, the high electron binding energy peaks correspond to the chain style structures, and the low electron binding energy peaks correspond to the Na-N-Na-N rhombic structures or their derivatives. For the (NaSCN)2(H2O)n - clusters at n = 3-5, the Na-N-Na-N rhombic structures are the dominant structures, the rhombic four-membered rings start to open at n = 4, and the solvent separated ion pair (SSIP) type of structures start to appear at n = 6. For the neutral (NaSCN)2(H2O)n clusters, the Na-N-Na-N rhombic isomers become the dominant starting at n = 3, and the SSIP type of structures start to appear at n = 5 and become dominant at n = 6. The structural evolution of (NaSCN)2(H2O)n -/0 (n = 0-7) confirms the possible existence of ionic clusters such as Na(SCN)2 - and Na2(SCN)+ in NaSCN aqueous solutions.

The effect of ion pairs on coacervate-driven self-assembly of block polyelectrolytes.

The incorporation of oppositely charged polyelectrolytes into a block copolymer system can lead to formation of microphase separated nanostructures driven by the electrostatic complex between two oppositely charged blocks. It is a theoretical challenge to build an appropriate model to handle such coacervate-driven self-assembly, which should capture the strong electrostatic correlations for highly charged polymers. In this paper, we develop the self-consistent field theory considering the ion paring effect to predict the phase behavior of block polyelectrolytes. In our model, two types of ion pairs, the binding between two oppositely charged monomers and the binding between charged monomers and counterions, are included. Their strength of formation is controlled by two parameters Kaa and Kac, respectively. We give a detailed analysis about how the binding strength Kac and Kaa and salt concentration affect the self-assembled nanostructure of diblock polyelectrolyte systems. The results show that the binding between two oppositely charged blocks provides driven force for microphase separation, while the binding between charged monomers and counterions competes with the polyion pairing and thus suppresses the microphase separation. The addition of salt has a shielding effect on the charges of polymers, which is a disadvantage to microphase separation. The phase diagrams as a function of polymer concentration and salt concentration at different situations are constructed, and the influence of Kaa, Kac, and charged block composition fa is analyzed in depth. The obtained phase diagrams are in good agreement with currently existing experimental and theoretical results.

Chemisorption of CO2on diaminated silica as bicarbonates and different types of carbamate ammonium ion pairs

Direct excitation and {1H}13C-CPMAS NMR allowed detecting carbamate–ammonium ion pairs, carbamic acid and bicarbonate species in amine-modified silica sorbents.

Microsolvation of Sodium Thiocyanate in Water: Gas Phase Anion Photoelectron Spectroscopy and Theoretical Calculations.

We studied NaSCN(H2O)n- clusters in the gas phase using size-selected anion photoelectron spectroscopy. Vertical detachment energies (VDEs) of NaSCN(H2O)n- (n = 0-6) clusters were obtained in the experiment. Structures of NaSCN(H2O)n- (n = 0-6) clusters and their corresponding neutral counterparts were investigated by theoretical calculations. Our studies show that the Na-NCS type of structures rather than the Na-SCN type of structures are dominant in the gas phase for both anionic and neutral NaSCN(H2O)n clusters. For NaSCN(H2O)n- anions, the contact ion pair (CIP) and solvent-separated ion pair (SSIP) type of structures coexist at n = 2 and 3, the SSIP type of structures become dominant at n ≥ 4. For neutral NaSCN(H2O)n, the CIP type of structures are dominant from n = 1 to 6 and the SSIP type of structures start to appear at n = 6. The gas phase structures in this work support the existence of ion clustering in concentrated NaSCN aqueous solutions.

Disulfonated azo dyes: metal coordination and ion-pair separation in twelve MII compounds of Ponceau Xylidine and Crystal Scarlet.

The structures of seven divalent metal cation compounds of Ponceau Xylidine {PX; systematic name of dication: 4-[2-(3,4-dimethylphenyl)hydrazin-1-ylidene]-3-oxo-3,4-dihydronaphthalene-2,7-disulfonate}, also known as Acid Red 26, CI 16150, and of five divalent metal cation compounds of Crystal Scarlet {CS; systematic name of dication: 8-[2-(naphthalen-1-yl)hydrazin-1-ylidene]-7-oxo-7,8-dihydronaphthalene-1,3-disulfonate}, also known as Acid Red 44, CI 16250, are presented. These are hexaaquamagnesium(II) PX dimethylformamide (DMF) monosolvate, [Mg(H2O)6](C18H14N2O7S2)·C3H7NO, (I); heptaaquacalcium(II) PX 2.5-hydrate, [Ca(H2O)7](C18H14N2O7S2)·2.5H2O, (II); catena-poly[aqua(μ-DMF)tris(DMF)bis(μ3-PX)distrontium(II)], [Sr(C18H14N2O7S2)(C3H7NO)2(H2O)0.5]n, (III); the transition-metal series hexaaquametal(II) PX DMF monosolvate, [M(H2O)6](C18H14N2O7S2)·C3H7NO, where M (metal) = Co, (IV), Ni, (V), Cu, (VI), and Zn, (VII); heptaaquacalcium(II) CS monohydrate, [Ca(H2O)7](C20H13N2O7S2)·H2O, (VIII); octaaquastrontium(II) CS monohydrate, [Sr(H2O)8](C20H13N2O7S2)·H2O, (IX); catena-poly[[triaqua(DMF)barium(II)]-μ-CS], [Ba(C20H13N2O7S2)(C3H7NO)(H2O)3]n, (X); tetrakis(DMF)(CS)copper(II) monohydrate, [Cu(C20H13N2O7S2)(C3H7NO)4]·H2O, (XI); and catena-poly[[[aquatris(DMF)zinc(III)]-μ-CS] diethyl ether hemisolvate], {[Zn(C20H13N2O7S2)(C3H7NO)3(H2O)]·0.5C4H10O}n, (XII). In all cases, the structures obtained were solvates with dimethylformamide (DMF) and/or water present. The disulfonated naphthalene-based azo anions adopt hydrazone tautomeric forms. The structures of the Mg salt and of four transition-metal forms (M = Co, Ni, Cu and Zn) of PX are found to form an isostructural series. All have solvent-separated ion-pair (SSIP) type structures and the formula [M(H2O)6][PX]·DMF. The Ca salt of PX also has an SSIP structure, but has a higher hydration state, [Ca(H2O)7][PX]·2.5H2O. In contrast, the Sr salt of PX, [Sr(PX)(DMF)2(H2O)0.5]n forms a one-dimensional coordination polymer. Both the Ca and the Sr salt of CS have an SSIP structure, namely [Ca(H2O)7][CS]·H2O and [Sr(H2O)8][CS]·H2O, whilst the heavier Ba analogue, [Ba(CS)(DMF)(H2O)3]n, forms a one-dimensional coordination polymer. Unlike PX, two CS structures containing transition metals are found to be coordination complexes, [Cu(CS)(DMF)4]·H2O and {[Zn(CS)(DMF)3(H2O)]·0.5Et2O}n. This suggests that CS is a better ligand than PX for transition metals. The Cu complex forms discrete molecules with Cu in a square-pyramidal environment, whilst the Zn species is a one-dimensional coordination polymer based on octahedral Zn centres.

α-Deprotonation of a β-shielded acrylamide creates a distorted lithium 1-aminoallen-1-olate

The β-shielded acrylamide N,N-diisopropyl-α-(1,1,3,3-tetramethylindan-2-ylidene)acet-amide was prepared through ketone addition of an α-lithiated acetamide, followed by H2O elimination. Its α-deprotonation by n-butyllithium occurred readily in THF without any tendency towards addition reactions at C=O or C-β. The resultant single crystals of a dimeric lithio derivative had triple Li–O coordination and a weakly bonding, ion-pair type Li–C(α) relationship. In tert-butyl methyl ether as the solvent, up to seven pairs of diastereotopic nuclei (both 1H and 13C) established a CS-symmetric lithium 1-aminoallen-1-olate structure that is ascribed to either a thermal ground state or a very rapid (on the NMR time scales) oscillation between two chiral ground states that may resemble the solid-state structure.

Modified Screen-Printed and Carbon Paste as Ion-Selective Electrodes for the Determination of Ramipril Drug in Pharmaceutical and Biological Samples

Ramipril was a prodrug and it was an angiotensin converting enzyme (ACE) inhibitor which can be used to treat congestive heart failure and hypertension. In this study, the electro activity and the performance characteristics of modified screen-printed (MSPEs) and carbon paste (MCPEs) electrodes with different types of ion pairs had been studied in order to determine ramipril (RAM) drug in pure solution, pharmaceutical formulations and biological fluid samples. The ion pair formation between RAM and phosphomolybdic acid (PMA) or phosphotungstic acid (PTA) or sodium teteraphenyl borate (Na-TPB) was the basis of preparation of modified ion selective electrodes used in this study. The surface analysis of the electrodes was studied using scanning electron microscope (SEM) and X-ray diffraction (XRD). The electrodes showed linear response with good Nernstian slope of 58.50±1.08, 59.00±0.96, 59.60±0.73 mV decade-1 for MSPEs modified with RAM-TPB, RAM-PMA and RAM-PTA ion pairs, respectively, and 59.20±0.96, 58.90±1.01 mV decade-1 for MCPEs modified with RAM-TPB and RAM-PTA ion pairs, respectively, over the concentration range from 5.0 x 10-7 to 1.0 x 10-2 mol L-1. Although, the two types of electrodes provided response time of about 4 s for MSPEs and 5 s for MCPEs and exhibited lifetimes of 99 to 92 days for MSPE electrodes and 67 days for both electrodes of MCPEs on pH range from 2 to 5 for MSPEs and 2 to 4 for MCPEs. They showed high thermal stability according to the isothermal coefficients values. Selectivity coefficients of RAM sensors relative to a number of potential interfering materials were investigated. The developed method was found to be simple, precise and accurate when compared with the reported method.

Ionic association analysis of LiTDI, LiFSI and LiPF6 in EC/DMC for better Li-ion battery performances.

New lithium salts such as lithium bis(fluorosulfonyl)imide (LiFSI) and lithium 4,5-dicyano-2-(trifluoromethyl)imidazole-1-ide (LiTDI) are now challenging lithium hexafluorophosphate (LiPF6), the most used electrolyte salt in commercial Li-ion batteries. Thus it is now important to establish a comparison of these electrolyte components in a standard solvent mixture of ethylene carbonate and dimethyl carbonate (EC/DMC: 50/50 wt%). With this aim, transport properties, such as the ionic conductivity, viscosity and 7Li self-diffusion coefficient have been deeply investigated. Moreover, as these properties are directly linked to the nature of the interionic interactions and ion solvation, a better understanding of the structural properties of electrolytes can be obtained. The Li salt concentration has been varied over the range of 0.1 mol L−1 to 2 mol L−1 at 25 °C and the working temperature from 20 °C to 80 °C at the fixed concentration of 1 mol L−1. Experimental results were used to investigate the temperature dependence of the salt ion-pair (IP) dissociation coefficient (αD) with the help of the Walden rule and the Nernst–Einstein equation. The lithium cation effective solute radius (rLi) has been determined using the Jones–Dole–Kaminsky equation coupled to the Einstein relation for the viscosity of hard spheres in solution and the Stokes–Einstein equation. From the variations of αD and rLi with the temperature, it is inferred that in EC/DMC LiFSI forms solvent-shared ion-pairs (SIP) and that, LiTDI and LiPF6 are likely to form solvent separated ion-pairs (S2IP) or a mixture of SIP and S2IP. From the temperature dependence of αD, thermodynamic parameters such as the standard Gibbs free energy, enthalpy and entropy for the ion-pair formation are obtained. Besides being in agreement with the information provided by the variations of αD and rLi, it is concluded that the ion-pair formation process is exergonic and endothermic for the three salts in EC/DMC.

Ion selective carbon paste electrodes based on ion pair formation for determination of Tetra-n-butyl ammonium bromide

In this study, ion pairs formed between tetrabutyl ammonium bromide as surfactant and ion pairing agents as phosphotungetic acid (PTA), phosphomolybdic acid (PMA) and sodium tetraphenyl borate (NaTPB) have been used as electroactive materials for preparation of modified carbon paste electrodes (CPEs) selective to tetra-n-butyl ammonium bromide (TBAB) surfactant. Type and content of the different ion pairs on the performance of CPEs were studied. It was found that the best contents were, 15 mg of TBA-TPB (electrode I), 15 mg TBA-PTA (electrode II) and 6 mg TBA-PMA (electrode III) ion pairs, which gave the best Nernstian slope values of 59.41±0.31, 59.26±0.45 and 59.95±0.35 mVdecade-1, respectively. These fabricated electrodes exhibited suitable response to TBAB in a concentration range from 1.0x10−6 to 1.0x10-2 mol L-1 with lower detection limit of 1.0x10-6 mol L-1. These fabricated electrodes exhibited fast response time of about 3, 7 and 6 s under working pH range of 3-8, 5-8 and 5-9 for electrodes I, II and III, respectively. The results obtained were satisfactory with excellent percentage recovery comparable and sometimes better than those obtained by other routine methods for the assay of TBAB surfactant.

Structural parameters of the nearest environment of ions in aqueous solutions of ytterbium chloride

The radial distribution functions (RDFs) of aqueous solutions of ytterbium chloride were calculated using previously collected X-ray diffraction data for a wide range of solution concentrations under ambient conditions. Different solution structure models were constructed. Theoretical RDFs were calculated for each model. The optimum models for all systems studied were chosen based on the best fit between the theoretical and experimental RDFs. Quantitative characteristics of the nearest environment of Yb3+ and Cl– ions in solutions, namely, the coordination number, interparticle distances, and types of ion pairs were determined. The average number of water molecules in the first coordination sphere of the cation decreases from 8.2 to 6.0 as the solution concentration increases. The structure of all systems investigated is governed by non-contact ion associates throughout the concentration range studied.

Is the Solution Activity Derivative Sufficient to Parametrize Ion-Ion Interactions? Ions for TIP5P Water.

Biomolecular processes involve hydrated ions, and thus molecular simulations of such processes require accurate force-field parameters for these ions. In the best force-fields, both ion-water and anion-cation interactions are explicitly parametrized. First, the ion Lennard-Jones parameters are optimized to reproduce, for example, single ion solvation free energies; then ion-pair interactions are adjusted to match experimental activity or activity derivatives. Here, we apply this approach to derive optimized parameters for concentrated NaCl, KCl, MgCl2, and CaCl2 salt solutions, to be used with the TIP5P water model. These parameters are of interest because of a number of desirable properties of the TIP5P water model, especially for the simulation of carbohydrates. The results show, that this state of the art approach is insufficient, because the activity derivative often reaches a plateau near the target experimental value, for a wide range of parameter values. The plateau emerges from the interconversion between different types of ion pairs, so parameters leading to equally good agreement with the target solution activity or activity derivative yield very different solution structures. To resolve this indetermination, a second target property, such as the experimentally determined ion-ion coordination number, is required to uniquely determine anion-cation interactions. Simulations show that combining activity derivatives and coordination number as experimental target properties to parametrize ion-ion interactions, is a powerful method for reliable ion-water force field parametrization, and gives insight into the concentration of contact or solvent shared ion pairs in a wide range of salt concentrations. For the alkali and halide ions Li+, Rb+, Cs+, F-, Br-, and I-, we present ion-water parameters appropriate at infinite dilution only.

Gas-Phase Spectroscopic Signatures of Carboxylate-Li(+) Contact Ion Pairs: New Benchmarks For Characterizing Ion Pairing in Solution.

The coexistence of several types of ion pairs in solution together with their elusive nature hampers their experimental characterization, which relies in practice on theoretical models resorting to numerous approximations. In this context, a series of isolated contact ion pairs between a lithium cation and phenyl-tagged carboxylate anions of various lengths (Ph-(CH2)n-COO(-), n = 1-3) has been investigated in a conformer-selective manner by IR and UV laser spectroscopy, in conjunction with quantum chemistry calculations. The typical gas-phase IR signature of the bidentate structure formed between the carboxylate moiety and Li(+) has thus been obtained in the CO2(-) stretch region. In addition to the cation-anion interaction, a cation-π interaction occurs simultaneously in the largest system investigated (n = 3). The resulting distorted ion pair structure has been evidenced from both the IR signature of the CO2(-) stretches and the unique vibrationally resolved UV spectroscopy of a phenyl ring interacting with a cation. Such specific spectroscopic signatures of contact ion pairs provide experimental benchmarks, alternative to theoretical predictions, that can assist the assignment of vibrational spectra in solution.

Charge Tags for Most Comprehensive ESI-MS Monitoring of Morita-Baylis-Hillman (MBH)/aza-MBH Reactions: Solid Mechanistic View and the Dualistic Role of the Charge Tagged Acrylate.

Neutral and charge tagged reagents were used to investigate the mechanism of the classical Morita-Baylis-Hillman (MBH) reaction as well as its aza-version using mass spectrometry with electrospray ionization (ESI-MS). The use of an acrylate (activated alkene) with a methylimidazolium ion as a charge tag eliminates the requirement for adding acids as ESI(+) additives, which are normally used to favor protonation and therefore detection of reaction partners (reagents, intermediates, and products) by ESI(+)-MS. For both charge tagged reactions (MBH/aza-MBH), most reactants, intermediates, and the final adducts were efficiently detected in the form of abundant doubly and singly charged ions. Characterization of the reactions partners was performed via both tandem mass spectrometry (ESI(+)-MS/MS) and accurate m/z measurements. The charge tagged reactions also showed faster conversion rates when compare to the neutral reaction, indicating a dualistic role for the charge tagged acrylate. It acts as both the reagent and a cocatalyst due to the inherent ionic-coordination nature of the methylimidazolium ion, which stabilizes the zwitterionic intermediates and reagents through different types of coordination ion pairs. Hemiacetal intermediates for the rate-limiting proton transfer step were also intercepted and characterized for both classical and aza-MBH charge tagged reactions.

Synthesis, crystal structure, and magnetic property of a cyano involved ion-pair complex based on macrocyclic metallic tecton and [Ni(CN)4]2–

A cyano-bridged nickel(II) complex [NiL]2{[NiL][Ni(CN)4]2}2 · H2O (III) (L = 1,3,10,12,15,18-hexaazatetracyclo[16,2,1,112.15,04.9]docosane), based on macrocyclic metallic tecton and diamagnetic [Ni(CN)4]2– has been synthesized and characterized by physico-chemical methods, as well as single crystal X-ray determination (CIF file CCDC no. 1038635). The crystal belongs to orthorhombic, space group: P212121, with a = 15.410(3), b = 15.752(3), c = 19.134(4) A, Mr = 2137.74 g mol–1, Z = 2, V = 4644.6(16) A3 (CIF file CCDC no. 1038635). Single X-ray diffraction analysis reveals that complex I shows a ion-pair type structure which consists of two fragments [NiL]2+ and {[NiL][Ni(CN)4]2}2–. In this complex, each {[NiL][Ni(CN)4]2}2– binds two [NiL]2+, resulting a hydrogen-bonded 1D chain. In additional, the magnetic properties were studied.

Exploring Ion-Ion Interactions in Aqueous Solutions by a Combination of Molecular Dynamics and Neutron Scattering.

Recent advances in computational and experimental techniques have allowed for accurate description of ion pairing in aqueous solutions. Free energy methods based on ab initio molecular dynamics, as well as on force fields accounting effectively for electronic polarization, can provide quantitative information about the structures and occurrences of individual types of ion pairs. When properly benchmarked against electronic structure calculations for model systems and against structural experiments, in particular neutron scattering, such force field simulations represent a powerful tool for elucidating interactions of salt ions in complex biological aqueous environments.