Radial and orientational solvation structure of the sodium chloride ion pair in dimethyl sulfoxide

Abstract

The structures of the solvation shells around each ion of the Na ϩ -Cl Ϫ ion pair in liquid dimethyl sulfoxide ͑DMSO͒ have been studied in terms of the ion-solvent radial distribution functions ͑RDFs͒ and the ion-solvent orientational distribution functions ͑ODFs͒ at the three interionic separations of 2.6 Å, 4.9 Å, and 7.2 Å. The solvation shell around the sodium ion consists of only three DMSO molecules at the ion-ion separation of 2.6 Å and this number grows to five DMSO molecules at interionic separation 4.9 Å and beyond. These are in contrast with the octahedral solvation shells around sodium ion in water at all ion-ion separations, where the chloride ion replaces a molecule of water only at a short interionic distance of 2.7 Å. The orientational structure of the solvent around the ion pair has been probed by dividing the DMSO solvent into five spatial regions and analyzing the angular distributions in each region. In the shell near the Na ϩ ion, the orientation of the sulphur-oxygen vector in DMSO is sharply peaked about 155°away from the sodium-sulphur vector for all the three interionic distances. Similarly, the orientation of the DMSO dipole vector is also sharply peaked about 155°away from the sodium-DMSO center of mass ͑COM͒ vector. In the shell near the Cl Ϫ ion, the orientation of the sulphur-oxygen vector with respect to the chloride-sulphur vector shows broader peaks in the range 20°-100°. The solvent dipole vector gets oriented in a similar fashion with respect to the chloride-COM vector in this shell. In the regions far from the Na ϩ and Cl Ϫ solvation shells, both the sulphur-oxygen vector and the solvent dipole vector have broad distributions covering all the angles except the parallel and the antiparallel alignments. The angles between the Na ϩ -S-O plane ͑or the Cl Ϫ -S-O plane͒ and the S-Na ϩ -Cl Ϫ plane do not show a preference for any specific inclination, in any of the spatial regions around the ion pair. These broad distributions are indicative of a weaker second shell around the ion pair in DMSO than the second shell found in water and are a consequence of the near absence of hydrogen bonding in DMSO.

Ultrafast Infrared Spectroscopy of Vibrational States Prepared by Photoinduced Electron Transfer in (CN)5FeCNRu(NH3)5-

“…It may be that the optically induced electron transfer which moves charge away from the iron also causes the sodium counterion to move far enough away from the complex to allow a solvent molecule to occasionally slip into the void. The characteristic time for solvent-separated ion pair to reconvert to an ion pair is expected to be nanoseconds or longer. , …”

Ligand‐Exchange Processes on Solvated Lithium Cations: DMSO and Water/DMSO Mixtures

“…[28] A variety of theoretical and experimental studies on liquid DMSO, [30][31][32][33][34] water/DMSO mixtures, [35][36][37][38][39][40] DMSO/nonaqueous electrolyte solutions [41,42] and solutions of biomolecules in DMSO [43][44][45] have been performed in recent years to understand the physical properties of DMSO solutions. Solutions of alkalimetal ions, mostly Li + , in DMSO have also been investigated experimentally [46][47][48][49] and theoretically, [41,[50][51][52][53] as well as in water/ DMSO mixtures [54][55][56] and in other solvent combinations. [57][58][59] One of the first reports on the utilisation of 7 Li NMR in the investigation of LiClO 4 in various solvents (including DMSO) was published by Maciel et al [88] In DMSO, no evidence for contact ion pairing was observed [56,60] as might be expected, for instance, in THF (DN = 7.4).…”

Nonideality in diffusion of ionic and neutral solutes and hydrogen bond dynamics in dimethyl sulfoxide–chloroform mixtures of varying composition

“…Dimethyl sulfoxide (DMSO) is an important industrial solvent and is widely used in chemistry and biology because of its unique solvent properties 1, 2. In the past few years, there have been numerous studies on aqueous3–24 and nonaqueous25–30 mixtures containing DMSO. DMSO–chloroform mixtures have been found to show interesting nonideal behavior in their thermodynamic31–36 and spectral41, 42 properties with variation of composition.…”