| Autor: |
Wooldridge, Robert, Fisher, Mark, Ritzhaupt, Gary, Devlin, J. Paul |
| Předmět: |
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| Zdroj: |
Journal of Chemical Physics; 4/15/1987, Vol. 86 Issue 8, p4391, 5p |
| Abstrakt: |
Infrared and Raman Spectra for alkali-metal nitrate solutions in dimethylsulfoxide (DMSO) have been measured as a function of concentration (0.5 to 2.0 M) and temperature (298 to 400 K) to determine the influence of temperature on structural changes that favor the incorporation of the nitrate anion into the solvation shell of the M+ cations. It is apparent from the spectra observed at elevated temperatures that this contact pairing of the ions in liquid DMSO occurs endothermically. It is also shown, by invoking the known spectra of the solvates (DMSO)3·LiNO3 and (DMSO)4·LiNO3 that are available from low temperature matrix-solvation measurements, that partial desolvation of the contact-ion-pair solvates occurs endothermically over this temperature range. These observations are interpreted as evidence that the energetics for the structural changes that lead to anion incorporation into the cation inner coordination sphere are dominated by the endothermic partial desolvation of the ions (in particular the cation). The DMSO solvates of the contact ion pair dominate the Raman spectra at 400 K for all of the alkali metal nitrates provided the concentration exceeds 1.0 M. In the case of LiNO3, polarization Raman data indicate that the cation-anion binding for (DMSO)3·LiNO3 is bidentate while that for (DMSO)4·LiNO3 is monodentate. This switch in cation–anion binding has been anticipated from considerations of steric repulsive forces in the inner coordination shell of the Li+ cation but has proved difficult to document. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
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