Complexation of Iron(III) with Thiocyanate Ions in Aqueous Solution

Abstract

Spectrophotometry and calorimetric studies of the complexation of iron(III) with thiocyanate ions have been performed in an aqueous solution containing 1 mol dm-3 NaC104 or NH4CIO4 as a constant ionic medium at 25° C. Spectrophotometry; titration data were well explained in terms of the formation of [Fe(SCN)]2+, [Fe(SCN)2]+ and [Fe(SCN)3], and their formation constants and individual electronic spectra were determined. The [Fe(SCN)]2+, [Fe(SCN)2]+ and [Fe(SCN)3] complexes exhibit absorption maxima at 450 - 500 nm. Enthalpies and entropies for the formation of the [Fe(SCN)]2+, [Fe(SCN)2]+ and [Fe(SCN)3] complexes were also determined from calorimetric titration data. On the basis of these thermodynamic quantities, it is postulated that the [Fe(SCN)]2+, [Fe(SCN)2]+ and [Fe(SCN)3] complexes have a six-coordinate octahedral structure. © 1992, The Japan Society for Analytical Chemistry. All rights reserved.