Ion-ion-solvent interactions in solution. Aqueous solutions of nitrates of cations from Groups 2A and 3A

1982 ◽  
Vol 35 (9) ◽  
pp. 1793 ◽  
Author(s):  
DW James ◽  
RL Frost
Keyword(s):  
Aqueous Solutions ◽  
Ion Pairs ◽  
Ion Pair ◽  
Band Shape ◽  
Nitrate Ion ◽  
Solvent Interactions ◽  
Contact Ion Pair ◽  
Component Band ◽  
Association Equilibria ◽  
Contact Ion Pairs

Association equilibria in aqueous solutions of the salts Be(NO3)2, Ca(NO3)2 Sr(NO3)2, Ba(NO3)2 and Al(NO3)3 have been studied through band shape and component band analysis of the non-degenerate, Raman-active V1 vibrational band of the nitrate ion. Band contributions due to the aquated nitrate ion, solvent-separated ion pair, and contact ion pair were made for all salts. The nature of the contact ion pair was shown to be different in the presence of Be2+ and Al3+ from that seen for the other salts. This difference was associated with a strongly directional perturbation of the nitrate ion. For all salts the solvent-separated ion pair species was present in the lowest concentration solution studied (as low as 0.05 M). At intermediate concentrations the solvent separated ion pair species was the dominant solution species while at the higher concentrations the species with anion and cation in contact becomes appreciable. For solutions of Ca(NO3)2 some evidence for a more extensive ion aggregate was found at the highest concentration (5M). Equilibrium quotients calculated from the spectroscopic components are in reasonable agreement with previous values determined by equilibrium and transport measurements, and it is suggested that these previous determinations detected the presence of solvent-separated ion pairs rather than contact ion pairs.

scholarly journals When spectroscopy fails: The measurement of ion pairing

2006 ◽  
Vol 78 (8) ◽  
pp. 1571-1586 ◽  
Author(s):  
Glenn Hefter
Keyword(s):  
Metal Ion ◽  
Chemical Speciation ◽  
Ion Pairs ◽  
Ion Association ◽  
Ion Pair ◽  
Association Constants ◽  
Spectroscopic Techniques ◽  
Association Equilibria ◽  
Solvent Molecules ◽  
Contact Ion Pairs

Spectroscopic techniques such as UV/vis, NMR, and Raman are powerful tools for the investigation of chemical speciation in solution. However, it is not widely recognized that such techniques do not always provide reliable information about ion association equilibria. Specifically, spectroscopic measurements do not in general produce thermodynamically meaningful association constants for non-contact ion pairs, where the ions are separated by one or more solvent molecules. Such systems can only be properly quantified by techniques such as dielectric or ultrasonic relaxation, which can detect all ion-pair types (or equilibria), or by traditional thermodynamic methods, which detect the overall level of association. Various types of quantitative data are presented for metal ion/sulfate systems in aqueous solution that demonstrate the inadequacy of the major spectroscopic techniques for the investigation of systems that involve solvent-separated ion pairs. The implications for ion association equilibria in general are briefly discussed.

Ion-ion-solvent interactions in solution. I. Solutions of LiClO4 in acetone

1982 ◽  
Vol 35 (9) ◽  
pp. 1775 ◽  
Author(s):  
DW James ◽  
RE Mayes
Keyword(s):  
Raman Band ◽  
Ion Pairs ◽  
Ion Association ◽  
Solvent Interactions ◽  
Solvation Numbers ◽  
Solvated Ions ◽  
Component Band ◽  
Li Ion ◽  
Contact Ion Pairs ◽  
Association Equilibrium

Vibrational spectra and 7Li, 13C and 35Cl n.m.r. spectra have been obtained for solutions of LiClO4 in acetone for salt concentrations from 0.05 to 6 M. Infrared spectra give qualitative indications of ion association. Analysis of the Raman band due to C-C stretching in acetone yields solvation numbers for the Li+ ion of the order of 3. Component band analysis of the ClO4- symmetric stretching vibrational band and the various n.m.r. spectra lead to the identification of solvent-separated ion pairs, contact ion pairs and ion aggregates, in addition to free solvated ions. The dependence on salt concentration of all four species has been determined. The association quotient for the association equilibrium (Li+)s(ClO4)- ↔ [Li+(acetone)ClO4-)s was determined to be 1.4 � 0.3 dm3 mol-1.

ESR- und ENDOR-Untersuchungen von p-Benzosemichinon-Diarylthallium-Ionenpaaren / ESR- and ENDO R-Investigations of p-Benzosemiquinone-Diarylthallium Ion Pairs

1984 ◽  
Vol 39 (10) ◽  
pp. 1416-1424 ◽  
Author(s):  
Hartmut B. Stegmann ◽  
Karl B. Ulmschneider ◽  
Paul Schuler ◽  
Thomas Jülich ◽  
Klaus Scheffler
Keyword(s):  
Ion Pairs ◽  
Organometallic Compounds ◽  
Ion Pair ◽  
Coupling Constants ◽  
Paramagnetic Species ◽  
Contact Ion Pair ◽  
Basic Solutions ◽  
G Value ◽  
Contact Ion Pairs ◽  
Doublet Splitting

Diarylthallium hydroxides react very smoothly in organic solvents with hydroquinones to stable paramagnetic complexes. This reaction has been investigated with two ligands and several organometallic compounds in 8 different solvents. In basic solutions clearly two paramagnetic species can be detected by ESR spectroscopy. One component exhibits a large doublet splitting assigned to the thallium counterion and the second radical does not show any metal coupling. The relative concentrations of both radicals depend strongly on the solvent and the temperature. Therefore, a slow equilibrium betw een a contact ion pair and a solvent separated ion pair is assumed. The thermodynamic parameters are determined to ⊿H = 0.8 kcal/mol, ⊿G293 = -0.1 kcal/mol, ⊿S = 3.04 cl/mol. The proton and thallium coupling constants as well as the g-value of the contact ion pair show a rem arkable temperature dependence. The signs of proton splitting constants are determined by ENDOR-TRIPLE investigations. The change of the electronic structure of the radical anion by formation of a contact ion pair is discussed. For interpretation of these results we assumed a fast equilibrium between different conformations of the contact ion pair according to behaviour of comparable aroxyl radicals. Therefore, the systems investigated allow a simultaneous observation of solvent separated and different contact ion pairs.

Synthesis, Structure, and Ion Pair Dynamics of β-Diketiminato-Supported Organoscandium Contact Ion Pairs

2005 ◽  
Vol 24 (6) ◽  
pp. 1173-1183 ◽  
Author(s):  
Paul G. Hayes ◽  
Warren E. Piers ◽  
Masood Parvez
Keyword(s):  
Ion Pairs ◽  
Ion Pair ◽  
Contact Ion Pairs

Ion Ion Solvent Interactions in Solution .XI. Spectroscopic Studies of Group-2 Perchlorates in Acetone

1986 ◽  
Vol 39 (1) ◽  
pp. 149 ◽  
Author(s):  
DW James ◽  
PG Cutler
Keyword(s):  
Raman Spectra ◽  
Spectroscopic Studies ◽  
Solvent Interactions ◽  
Solvation Numbers ◽  
Steric Crowding ◽  
Component Band ◽  
Group 2 ◽  
Association Equilibria ◽  
High Level ◽  
Ion Species

Solutions of Mg(ClO4)2 and Sr (ClO4)2 in acetone have been studied at various concentrations up to saturation by using infrared absorption, Raman scattering and multinuclear n.m.r (1H, 13C, 17O, 25Mg, 35Cl). Solvation numbers of c. 4.5 (Mg2+) and c. 5.5 (Sr2+) were determined from component band analysis of the c. 800 cm-1 acetone band in the Raman spectra. The solvent shell about the Mg2+ had a high level of steric crowding. There was a small amount of solvent-shared ion-pair formation at all oncentrations in solutions of Mg(ClO4)2 which showed little concentration dependence. In solutions of Sr (ClO4)2 there was evidence for the formation of both solvent-shared associated-ion species and ion-contact species. The solvent-shared species appeared to have two alternative configurations in one of which the anion was both polarized and highly hindered. There was a salt-promoted reaction in which the perchlorate was reduced to chloride and the solution darkened. This reaction prevented the use of Raman spectra to quantify the association equilibria.

Contact Ion Pair Formation between Hard Acids and Soft Bases in Aqueous Solutions Observed with 2DIR Spectroscopy

2013 ◽  
Vol 117 (49) ◽  
pp. 15306-15312 ◽  
Author(s):  
Zheng Sun ◽  
Wenkai Zhang ◽  
Minbiao Ji ◽  
Robert Hartsock ◽  
Kelly J. Gaffney
Keyword(s):  
Aqueous Solutions ◽  
Ion Pair ◽  
Pair Formation ◽  
Ion Pair Formation ◽  
Contact Ion Pair ◽  
2Dir Spectroscopy

Elektronentransfer und Kontaktionen-Bildung, 42 [1,2] Cyclovoltammetrische und ESR / ENDOR-Untersuchungen der Einelektronen-Reduktion von Diphenochinonen / Electron Transfer and Contact Ion Pair Formation, 42 [1,2] Cyclovoltammetric and ESR / ENDOR Investigations of the One-Electron Reduction of Diphenoquinones

1995 ◽  
Vol 50 (11) ◽  
pp. 1699-1716
Author(s):  
Andreas John ◽  
Hans Bock
Keyword(s):  
Radical Anion ◽  
Ion Pairs ◽  
Ion Pair ◽  
Pair Formation ◽  
Coupling Constants ◽  
Semiquinone Radical ◽  
Additional Information ◽  
Ion Pair Formation ◽  
Contact Ion Pair ◽  
The Difference

Semiquinone radical anions are prototype compounds for contact ion pair formation with metal counter cations. In order to investigate the still open question whether bulky alkyl groups can sterically interfere, diphenoquinone derivatives O=C(RC=CH)2C=C(HC=CR)2C=O with R = C(CH3)3, CH(CH3)2 and CH3 have been selected and the following ESR/ENDOR results are obtained for the alkaline metal cations: The tetrakis(tert-butyl)-substituted radical anion only adds Li⊕ and Na⊕, while K⊕ forms no ion pair. The 3,3ʹ,5,5ʹ-tetra(isopropyl)diphenoquinone radical anion is accessible to all cations Me⊕, although Rb⊕ and Cs⊕ seem to be present solvent-separated in solution. The tetramethyl-substituted radical anion unfortunately polymerizes rapidly. Additional information concerns the ESR/ENDOR proof for ion triple radical cation formation [Li⊕ M•⊖Li⊕]•⊕, or the difference in the coupling constants upon Me⊕ docking at one δ⊖O=C group, suggesting that about 87% of the spin density is located in the cation-free molecular half of the diphenoquinone radical anion. Based on the wealth of ESR/ENDOR information, crystallization of the contact ion pairs and their structural characterization should be attempted.

Solute–solvent interactions in the association of hexacyanoferrate(III) with group II A cations. A calorimetric study

1982 ◽  
Vol 60 (14) ◽  
pp. 1828-1831 ◽  
Author(s):  
Roberto Aruga
Keyword(s):  
Equilibrium Constants ◽  
Ion Pairs ◽  
Ion Pair ◽  
Pair Formation ◽  
Calorimetric Study ◽  
Thermodynamic Quantities ◽  
Gibbs Function ◽  
Direct Calorimetry ◽  
Solvent Interactions ◽  
Enthalpy Of Association

Enthalpy of association of hexacyanoferrate(III) ion with Mg(II), Ca(II), Sr(II), and Ba(II) cations has been determined by direct calorimetry. Using the equilibrium constants, Gibbs function and entropy were also obtained. Measurements were carried out in aqueous medium at 25 °C and ionic strength I = 0.1 mol L−1. Examination of the thermodynamic quantities obtained and calculation of the distance of closest approach between cation and anion show the presence of different desolvation processes for the metals studied. More particularly, solvent-separated ion pairs in the case of magnesium and contact pairs in the case of barium seem to be present. The presence of desolvation processes is uncertain for calcium and strontium. The ΔH0 and ΔS0 values show also an important influence from solvent-destructuring processes on ion pair formation.

scholarly journals Aqueous Contact Ion Pairs of Phosphate Groups with Na+, Ca2+ and Mg2+ – Structural Discrimination by Femtosecond Infrared Spectroscopy and Molecular Dynamics Simulations

2020 ◽  
Vol 234 (7-9) ◽  
pp. 1453-1474 ◽  
Author(s):  
Benjamin P. Fingerhut ◽  
Jakob Schauss ◽  
Achintya Kundu ◽  
Thomas Elsaesser
Keyword(s):  
Ion Pairs ◽  
Model System ◽  
Ion Pair ◽  
Pair Formation ◽  
Phosphate Group ◽  
Phosphate Ion ◽  
2D Ir ◽  
Dna And Rna ◽  
Contact Ion Pairs ◽  
Phosphate Groups

AbstractThe extent of contact and solvent shared ion pairs of phosphate groups with Na+, Ca2+ and Mg2+ ions in aqueous environment and their relevance for the stability of polyanionic DNA and RNA structures is highly debated. Employing the asymmetric phosphate stretching vibration of dimethyl phosphate (DMP), a model system of the sugar-phosphate backbone of DNA and RNA, we present linear infrared, femtosecond infrared pump-probe and absorptive 2D-IR spectra that report on contact ion pair formation via the presence of blue shifted spectral signatures. Compared to the linear infrared spectra, the nonlinear spectra reveal contact ion pairs with increased sensitivity because the spectra accentuate differences in peak frequency, transition dipole moment strength, and excited state lifetime. The experimental results are corroborated by long time scale MD simulations, benchmarked by density functional simulations on phosphate-ion-water clusters. The microscopic interpretation reveals subtle structural differences of ion pairs formed by the phosphate group and the ions Na+, Ca2+ and Mg2+. Intricate properties of the solvation shell around the phosphate group and the ion are essential to explain the experimental observations. The present work addresses a challenging to probe topic with the help of a model system and establishes new experimental data of contact ion pair formation, thereby underlining the potential of nonlinear 2D-IR spectroscopy as an analytical probe of phosphate-ion interactions in complex biological systems.

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