Spectrochemistry of solutions, part 23. Changes of enthalpy and entropy in the formation of contact ion pairs: A vibrational spectroscopic appraisal using thiocyanate and azide solutions

Chingakule, Dicky D.K.; Gans, Paul; Gill, J. B.; Longdon, Peter J.

doi:10.1007/bf00816846

Cited by 14 publications

(8 citation statements)

References 30 publications

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“…This is different from the scenario above room temperature where ion pairing is usually endothermic. 73 These results further support the assumption that the ion association above and below the TMD (aq) is controlled by different factors. The intercept for the curve (Supporting Information Figure S6) generates a standard entropy at 25 °C, ΔS°= −95 J•mol −1 •K −1 .…”

Section: Discussionsupporting

confidence: 73%

“…The slope gives a negative Δ H ° = −7268 J·mol –1 ·K –1 , indicating an exothermic process for ion pairing, which is favored at lower temperature. This is different from the scenario above room temperature where ion pairing is usually endothermic . These results further support the assumption that the ion association above and below the TMD (aq) is controlled by different factors.…”

Section: Discussionsupporting

confidence: 50%

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Enhanced Formation of Solvent-Shared Ion Pairs in Aqueous Calcium Perchlorate Solution toward Saturated Concentration or Deep Supercooling Temperature and Its Effects on the Water Structure

Lobanov

Bai

et al. 2019

J. Phys. Chem. B

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As a candidate of Martian salts, calcium perchlorate ) 2 ] has the potential to stabilize liquid water on the Martian surface because of its hygroscopicity and low freezing temperature when forming aqueous solution. These two properties of electrolytes in general have been suggested to result from the specific cation−anion−water interaction (ion pairing) that interrupts the structure of solvent water. To investigate how this concentration-dependent and temperature-dependent ion pairing process in aqueous Ca(ClO 4 ) 2 solution leads to its high hygroscopic property and the extreme low eutectic temperature, we have conducted two sets of experiments. First, the effects of concentration on aqueous calcium perchlorate from 3 to 7.86 m on ion pairing were investigated using Raman spectroscopy. Deconvolution of the Raman symmetric stretching band (ν 1 ) of ClO 4 − showed the enhanced formation of solvent-shared ion pairs upon increasing salt concentration at room temperature. We have confirmed that the low tendency of forming contact ion pairs in concentrated solution contributes to the high hygroscopicity of the salt. Second, the near eutectic samples were studied as a function of temperature by both combined differential scanning calorimetry−Raman spectroscopic experiments and in situ X-ray diffraction. The number of solvent-shared ion pairs was found to increase with decreasing temperature when cooled below the temperature of maximum density of the solution, driven by a change in water toward an ice-like structure in the supercooled regime. The massive presence of solvent-shared ion pairs in turn limits the development of the long-range order in the tetrahedral networks of water molecules, which is responsible for the extremely low eutectic point and deep supercooling effects observed in the Ca(ClO 4 ) 2 −H 2 O system.

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Section: Discussionsupporting

confidence: 73%

Section: Discussionsupporting

confidence: 50%

Enhanced Formation of Solvent-Shared Ion Pairs in Aqueous Calcium Perchlorate Solution toward Saturated Concentration or Deep Supercooling Temperature and Its Effects on the Water Structure

Lobanov

Bai

et al. 2019

J. Phys. Chem. B

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“…In contrast, a negative slope is usually obtained in ln K versus 1/ T plots for formation of contact-ion pairs (or inner-sphere complexes) at ambient and elevated temperatures in aqueous solution above water's TMD and in nonaqueous solution. It follows that in the latter case contact-ion pairing is an endothermic process and Δ S is positive (see Table 1 in ref and Table 2 in ref ). Chingakule et al conclude from their studies of contact-ion pair formation in liquid ammonia that “the driving force in the ion association process derives from solvent−solute restructuring, and not the energy of interaction between the cation and anion”.…”

Section: Discussionmentioning

confidence: 89%

Increasing Contact-Ion Pairing as a Supercooled Water Anomaly. Estimation of the Fictive Temperature of Hyperquenched Glassy Water

1998

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In "dilute" aqueous D 2 O solution of calcium nitrate, contact-ion pairing increases on cooling from 300 to 240 K, despite simultaneous increase of water's dielectric permittivity. This increase in contact-ion pairing was quantified by FT-IR spectroscopic evaluation of nitrate's ν 2 band region. The bound/free nitrate area ratios strongly increase on supercooling in a nonlinear way, in a similar manner as the anomalous molar volume of supercooled water does, which suggests that both anomalies have a common origin in the structural changes of supercooled water. By extrapolation of bound/free nitrate area ratios, we conclude that water and the solute become, on hyperquenching into the glassy state, immobilized between 230 and 200 K. This is important for analysis of the thermodynamic path liquid water takes on quenching into the glassy state, and it gives a low-temperature limit where conformational changes can occur in a biomolecule during quenching of its aqueous solution into the glassy state.

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“…Solutions in liquid ammonia were prepared by condensation of this gaseous ammonia on to the preweighed salts in a graduated tube. From this measuring tube the solutions were transferred directly to the sample cells [3]. Concentrations (within ±1%) were obtained as mass of solid per unit volume of solvent for infrared spectra, and as mass of solid per unit mass of solution for the Raman spectra.…”

Section: Methodsmentioning

confidence: 99%

“…The use of vibrational spectroscopy can assist in probing the specific structural types of ion associate, and it is sometimes possible to establish the parameters which define the individual equilibria relating to their formation from the "free" solvated ions or other ion associates [3].…”

Section: Introductionmentioning

confidence: 99%

Infrared and Raman Spectroscopic Study of Ion Pairing of Strontium(ii) and Barium(ii) by Thiocyanates in Liquid Ammonia

Chingakule

Gans

Gill

2002

Bull. Chem. Soc. Eth.

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Spectrochemistry of solutions, part 23. Changes of enthalpy and entropy in the formation of contact ion pairs: A vibrational spectroscopic appraisal using thiocyanate and azide solutions

Cited by 14 publications

References 30 publications

Enhanced Formation of Solvent-Shared Ion Pairs in Aqueous Calcium Perchlorate Solution toward Saturated Concentration or Deep Supercooling Temperature and Its Effects on the Water Structure

Enhanced Formation of Solvent-Shared Ion Pairs in Aqueous Calcium Perchlorate Solution toward Saturated Concentration or Deep Supercooling Temperature and Its Effects on the Water Structure

Increasing Contact-Ion Pairing as a Supercooled Water Anomaly. Estimation of the Fictive Temperature of Hyperquenched Glassy Water

Infrared and Raman Spectroscopic Study of Ion Pairing of Strontium(ii) and Barium(ii) by Thiocyanates in Liquid Ammonia

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