Study of complex formation in Al(III)-thiocyanate-water system via Raman spectra and factor analysis

Abstract

Interaction between A1(III) and SCN - ion in aqueous solutions has been investigated using Raman spectroscopy. Eleven solutions with the SCN/A1(III) molar ratio from 0.5 to 10, have been studied. The systems of overlapped spectra in the v(CS) and v(CN) regions are analyzed by the methods of factor analysis. Spectra in the v(CN) and v(CS) regions have been reproduced using the first four and the first three vectors, respectively. The band areas in the v(CN) region have been determined by deconvolution and used for quantitative determination of species in solution. It is shown that the molar scattering coefficient of v(CN) is the same for all the species. The quantitative measurements of the Raman band intensity variation has revealed that Al(NCS)(H 2 O) 52+ , Al(NCS) 2 (H 2 O) 4+ and the two neutral, structurally different Al(NCS) 3 (H 2 O) 3 complexes are formed. The Al(NCS)(H 2 O) 52+ complex is present in the solutions with R ≤ 1, while the Al(NCS) 2 (H 2 O) 4+ appears in all the solutions with R ≥ 1. The neutral complexes are present for R > 4. In all the complexes, SCN - is coordinated through nitrogen as a terminal ligand. © 2001 Elsevier Science Ltd. All rights reserved.