Electronic Raman Spectra of a Low-Spin FeIII Porphyrin and Reexamination of the Vibrational Spectra of K3[Fe(CN)6] and [Fe(C5H5)2]BF4

Abstract

The resonance Raman spectra of (nBu4N)[Fe(CN)2TPP] ((nBu4: tetra(n-butyl)ammonium; TPP: m-tetraphenylporphyrin), K3 [Fe(CN)6] and [Fe(C5H5)2]BF4 have been investigated. A molecular electronic Raman (ER) effect at 545 cm-1 is observed for (nBu4N)[Fe(CN)2TPP]. The transition occurs between lower “Γ7” and upper “Γ8” level of the spin-orbit split ground state assuming pseudo-octahedral symmetry. In contrast to earlier studies no ER effect is detected for K3[Fe(CN)6] and [Fe(C5H5)2]BF4. For Raman shifts < 800 cm-1 only one strong Raman line is observed for [Fe(C5H5)2]BF4 at 311 cm-1, assigned to the iron ring stretch designated by ν4 (a1g in D5d). Due to a phase transition of K3[Fe(CN)6], two additional strong vibrational lines at 329 and 352 cm-1 appear in the Raman spectrum taken at 10 K. Their intensities show A "term" behaviour of the resonance Raman effect with overtones and combinations for both lines. These are components of the vibronic combinations with the ν6, ν7, and ν8 modes (t1u in Oh) in the IR spectra, too.