FT-Raman spectroscopic analysis of the most probable structures in aluminum chloride and tetrahydrofuran solutions

A study by concentration-dependent Raman spectroscopy is presented for solutions of AlCl3 in THF. The formation of small amounts of AlCl4- has been evidenced by the appearance of only one band at 348 cm(-1) in the most diluted salt solution. Another band at 330 cm(-1) starts rising with increasing salt concentration and it seems to belong to the [AlCl3(THF)(3)] complex. Indeed, this octahedral entity was confirmed by the quantitative analysis performed at the band envelope at 915 cm(-1). At this region, additional bands at 927 and 858 cm(-1) were observed and assigned to the C-C and C-O stretching modes, respectively, of THF molecules coordinated to the aluminum salt. Besides them, another band at 1042 cm(-1) clearly reveals the existence of this population of molecules. Although neutral octahedral complexes seem to be the major species in more concentrated salt solutions, the Raman spectra show the presence of complex ions in whole studied concentration range. (C) 2012 Elsevier B.V. All rights reserved.