A direct carbon-13 and nitrogen-15 nmr study of europium(iii)-isothiocyanate complex formation in aqueous solvent mixtures

Fratiello, Anthony; Kubo-Anderson, V.; Bolanos, E.; Ortega, J. V.; Perrigan, R. D.; Sáenz, Laura; Stoll, S. M.; Davidson, T.N.

doi:10.1007/bf02767919

Cited by 6 publications

(1 citation statement)

References 55 publications

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“…Determining the validity of the Law of Matching Water Affinities requires the robust determination of contact ion pair (CIP) formation in aqueous solution, but clear identification of CIP formation has proven to be challenging. A variety of spectroscopic methods have been utilized to study the equilibrium and dynamical properties of aqueous ionic solutions. − To date, dielectric relaxation spectroscopy has been the most useful technique for studying the interaction of ions in solution, providing information about the association and rotation of CIPs, solvent-separated ion pairs (SIPs), and doubly solvent-separated ion pairs (2SIP). − This sensitivity also makes analysis challenging because the contribution of each ion pair configuration exhibits complex, overlapping lineshapes.…”

Section: Introductionmentioning

confidence: 99%

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

Sun

Zhang

et al. 2013

J. Phys. Chem. B

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The interaction of charged species in aqueous solution has important implications for chemical, biological, and environmental processes. We have used 2DIR spectroscopy to study the equilibrium dynamics of thiocyanate chemical exchange between free ion (NCS(-)) and contact ion pair configurations (MNCS(+)), where M(2+) = Mg(2+) or Ca(2+). Detailed studies of the influence of anion concentration and anion speciation show that the chemical exchange observed with the 2DIR measurements results from NCS(-) exchanging with other anion species in the first solvation shell surrounding Mg(2+) or Ca(2+). The presence of chemical exchange in the 2DIR spectra provides an indirect, but robust, determinant of contact ion pair formation. We observe preferential contact ion pair formation between soft Lewis base anions and hard Lewis acid cations. This observation cannot be easily reconciled with Pearson's acid-base concept or Collins' Law of Matching Water Affinities. The anions that form contact ion pairs also correspond to the ions with an affinity for water and protein surfaces, so similar physical and chemical properties may control these distinct phenomena.

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