Solution and single crystal spectroscopic characterization of (PPh4)2[Fe(CN)5(imidazole)]·2H2O

The compound (PPh4)2[FeIII(CN)5(im)]·2H2O (1) together with its 13C labeled analogue have been synthesized (where im is imidazole) and characterized by UV/Vis, LD, IR, Raman and resonance Raman spectroscopy both in solution, powder and single crystalline form. The low spin state of the metal center, FeIII, was confirmed by MCD, EPR and 57Fe Mössbauer spectroscopies. Polarized Raman spectroscopic studies on a single crystal of 1 show the strong dependence of the stretching cyano ligand vibrations on crystal orientation relative to the direction of laser polarization and allows for assignment of all CN vibrational modes. Raman, UV/Vis absorption, LD and MCD spectroscopy both in the solid state and in solution state allowed for the discrimination of the effect of protonation of the imidazole ligand and hydrogen bonding to the cyano ligands on the complex. The combined spectroscopic data demonstrates that in addition to the protonation state of the imidazole, hydrogen bonding interactions with the cyano ligands both in the solid state as well as in solution have a profound influence on the electronic properties of 1.

► The compound (PPh4)2[FeIII(CN)5(im)]·2H2O (1) and its 13C isotopologues are reported.
► Complexes are characterized by UV/Vis, LD, MCD, IR, 57Fe Mössbauer, EPR, Raman and resonance Raman spectroscopy in solution, as powders and as single crystals.
► Polarized Raman spectroscopy allows for assignment of all CN vibrational modes.