Vibrational Spectral Studies of HClO4–DMSO Solutions: Hydrogen Bonding Data for Cation (DMSO)2H+
摘要
The solutions of anhydrous perchloric acid in dimethyl sulfoxide, denoted as HClO4·nDMSO (n = 2.0, 3.0, 3.2, 3.7, 8.2, and 16), as well as DClO4·2DMSO, HClO4·2DMSO-d6, and DClO4·2DMSO-d6, were first prepared and studied at room temperature using FTIR absorption and Raman spectroscopy in the frequency range 50–4000 cm–1 with measurements of the depolarization degree for Raman lines. The assignment of observed fundamental frequencies was suggested. It has been shown that the dissolution of HClO4/DClO4 in DMSO/DMSO-d6 results in the complete acid ionization with the formation of ion pairs, such as (DMSO)2H+ClO4–, (DMSO)2D+ClO4–, (DMSO-d6)2H+ClO4–, and (DMSO-d6)2D+ClO4–. Two solvent molecules inside the complex cation are held together by a proton through the formation of a strong hydrogen bond. The (DMSO)2H+ cation is characterized by a continuous IR band νas(OH+O) at 1250 cm–1 and a singlet IR band ν(SO) at 811 ± 10 cm–1; (DMSO-d6)2H+ is identified by a continuous band νas(OH+O) at 1256 cm–1 and a resonance doublet ν(SO) at 737 and 844 cm–1; (DMSO)2D+ shows a broad band νas(OD+O) with a maximum at ~ 877 cm–1 and a singlet ν(SO) at 800 ± 10 cm–1; (DMSO-d6)2D+ is characterized by a broad band νas(OD+O) at ~ 816 cm–1 and a resonance doublet ν(SO) at 724 and 870 cm–1. Physical property studies have shown that solutions with n = 2.0 can crystallize under the influence of small temperature variations. Therefore, their liquid state is metastable.