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

Abstract

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.

The influence of alkaline earth ions on the structural organization of acetone probed by the noncoincidence effect of the ν(CO) band: experimental and quantum chemical results

“…These bands are assigned to solvent-shared ion pairs and contact-ion pairs in ref. 34 ) Sr 2+ (see Fig. 6a) is located at B20 cm À1 lower than that of an isolated ion, reasonably accounting for the observed red shifted ClO 4 À vibration, whereas that of the monodentate form of the same cluster species (see Fig.…”

“…Both species are categorized as contact-ion pairs according ref. 34. Then it is possible to interpret (at least qualitatively) the observed band profile in the 930 cm À1 spectral region by free ClO 4…”

Solid state vibrational spectroscopy of anhydrous lithium hexafluorophosphate (LiPF6)

“…[5][6][7][8] The theoretical calculations on LiPF 6 [2] and experimental vibrational spectroscopy techniques have been used in other studies to further understand the cation-anion interactions. [2,[9][10][11][12][13][14] This salt is also known t o d e c o m p o s e t o L i F a n d P F 5 in air and ambient temperature, with additional decomposition of the PF 5 in the presence of water. [15] It is for this reason that it is sometimes kept as the more stable and easier to handle Li(C 5 H 5 N)PF 6 complex [16] .…”