Vibrational studies on the selective solvation of Na+ and ClO3- ions in dimethylformamide-formamide mixture

Raman and infrared spectra of sodium chlorate in binary mixture of N,N-dimethylformamide (DMF) and formamide (FA) were obtained. The addition of FA to the NaClO3-DMF system allow us to observe a new band at 1709cm(-1). This has been possible since the large dissociation of Na+ and ClO3- ions produced by the addition of FA helps to observe the coordination effect of DMF on the Na+ ions, in full agreement with the Gutmann donor number of this later. Quantitative measurements performed in the C=O stretching region in the binary mixture give a solvation number value for the sodium cation equal at 3 in full agreement with others authors. In the N-H stretching region of FA, the arising of the 3580 cm(-1) band is assigned to FA-ClO3- interactions via hydrogen bonding. In addition, our results show that the solvation number of the sodium cation remain constant in all concentration range studied. Such fact suggests that mixture of solvents with considerable differences in the donor-acceptor characters can be used to prepare electrolyte solutions where the ion pairs formation seems uncertain. (c) 2005 Elsevier B.V. All rights reserved.