Analysis of problematic complexing behavior of ferric chloride with N,N-dimethylformamide using combined techniques of FT-IR, XPS, and TGA/DTG

A problematic coordination behavior of highly hygroscopic FeCl3 in DMF solution was studied. From the compositional and structural analyses for the adduct of FeCl DMF using various techniques such as FTIR, elemental analysis, UV/vis, XPS, and TGA/DTG, it was found that the iron cation exists in the form of an Fe3+ cation and coordinates via the carbonyl oxygen atom of amide bond in DMF. The analyses of both FT-IR and XPS C 1s spectra for the adduct revealed that 2.1 molecules of DMF coordinate with a more electron-deficient Fe3+; otherwise 1.2 molecules of DMF coordinated with a relatively electron-rich Fe3+. The Cl 2p spectrum indicated that the electron-deficient Fe3+ coordinated with two chlorine ions and the electron-rich Fe3+ with four chlorines so that the chemical formula of the adduct is of [FeCl2(DMF)(1.2)(H2O)(2.7)](+)[FeCl4(DMF)(2.1)](-). The water molecules in the adduct were found chemisorbed rather than physisorbed, with a singular binding energy.