Spectroscopic and structural investigations of iron(III) isothiocyanates. A comparative theoretical and experimental study

摘要

A combined experimental and theoretical study on the molecular structure and vibrational spectra of [Fe(NCS)]~(2+) complex in the aqueous solution at the pH~2 ± 0.1 have been performed. Experimental Raman spectra of the iron(III) isothiocyanate with higher coordination number in the acidic aqueous solution have been analyzed. Molecular modeling of the iron(III) monoisothiocyanate complex was accomplished by the density functional theory (DFT) method using B3LYP and PBE1PBE functionals. Theoretical vibrational spectra of the iron(III) monoisothiocyanate were interpreted by means of the potential energy distributions (PEDs). The influence of different solvation models and position of SO~(2-)_4 ligand vs. NCS~- ligand upon its geometry and vibrational frequencies have been evaluated. The effect of H_2O/D_2O isotopic substitution on the experimental and calculated Raman spectra of iron(III) isothiocyanates has been examined. Procedures of Raman spectra subtraction have been applied for the extractions of weak and/or obscured Raman signals. As a result, the presence of bound SO~(2-)_4 ion and water molecules in the first coordination sphere in the acidic aqueous iron(III) isothiocyanate solution was confirmed. The vibrational assignments for the investigated iron(III) isothiocyanates were proposed here for the first time.