Structure of iron(III) and formation of iron(III) thiocyanato complexes in N,N-dimethylacetamide

Abstract The solvation structure of the iron(III) ion in N,N,-dimethylacetamide (DMA) has been determined by means of EXAFS (extended X-ray absorption fine structure) spectroscopy and the complex formation between iron(III) and thiocyanate ions has been calorimetrically and spectrophotometrically studied in DMA containing (C 2 H 5 ) 4 NClO 4 (0.4 mol dm −3 ) as a constant ionic medium at 25°C. The iron(III) ion is surrounded with six DMA molecules and has an octahedral [Fe(dma) 6 ] 3+ structure. Calorimetric and spectrophotometric titration data were well explained in terms of the formation of [Fe(SCN) n ] 3− n ) ( n = 1−6) and their formation constants, reaction enthalpies and entropies were determined. Electronic spectra of individual iron(III) thiocyanato complexes in DMA were also extracted. The complexation of iron(III) with thiocyanate ions in DMA is more favorable than that in N,N-dimethylformamide (DMF). The favorable formation is mainly due to the more negative reaction enthalpies in DMA than those in DMF, which is resulting from the larger steric interaction between the ligating DMA molecules around the iron(III) ion than the DMF ones.