Vibrational and Electronic Resonance Raman Effects in Tetraphenylporphyrinato Complexes of High-spin and Low-spin Iron(III)

A vibrational resonance Raman effect of the totally symmetric Fe - F stretching mode at 453 cm−1is observed for high-spin tetra-n-butylammonium di(fluoro)tetraphenylporphyrinatoferrate(III). Typical A-term scattering with a high intensity overtone progression is proposed to be due to coincidence of the excitation energy with a ‘trip-sextet’ transition at 21 000 cm−1. The complex salt crystallizes as a dichloromethane solvate in the monoclinic space group P12/n1 (No. 13): a = 12.287(3) Å, b = 12.381(4) Å, c = 20.761(5) Å,β = 105.05(2)°,Z = 4. The iron atom is in the centre of the slightly distorted porphyrinate core. The Fe - F distance is 1.907(2) Å, the averaged Fe - Npdistance 2.072(2) Å. There is no hydrogen bonding of the floride ligand to the cation or solvate. Contrary to the high-spin difluoro complex, a molecular electronic resonance Raman effect is detected for low-spin pyridine(cyano)- and -(thiocyanato( N )tetraphenylporphyrinatoiron(III) at 550 and 561/578 cm−1respectively. This Γ7 g→Γ8 gtransition is a consequence of the spin-orbit splitting of the2T2 gground state of low-spin FeIIIassuming octahedral symmetry. B-term scattering is active by excitation with 476.5 nm, effectively enhancing the intensity of non-totally symmetric electronic and vibrational transitions.

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Tetra(n-butyl)ammonium Dicyanotetraphenyl-porphyrinatomanganate(III); Crystal Structure and Electronic Resonance Raman and Absorption Spectra

Journal of Porphyrins and Phthalocyanines ◽

10.1002/(sici)1099-1409(199801/02)2:1<79::aid-jpp52>3.0.co;2-7 ◽

1998 ◽

Vol 02 (01) ◽

pp. 79-87 ◽

Cited By ~ 8

Author(s):

LUTZ GALICH ◽

HEINER HÜCKSTÄDT ◽

HEINER HOMBORG

Keyword(s):

Normal Values ◽

Raman Effect ◽

Resonance Raman ◽

Complex Salt ◽

Title Complex ◽

Molecular Electronic ◽

Orthorhombic Space Group ◽

Cell Parameters ◽

Electronic Resonance ◽

Ammonium Cyanide

The title complex salt has been isolated from a solution of chlorotetraphenylporphyrinatomanganese(III) and tetra(n-butyl)ammonium cyanide in dichloromethane. The complex salt crystallizes as a hydrate-dichloromethane solvate in the orthorhombic space group Pbca (no. 61) with cell parameters as follows: a = 21.491(5) Å, b = 21.706(5) Å, c = 28.489(5) Å, V = 13 290(5) Å3, Z = 8. The structure is that expected for a hexa-coordinated low-spin Mn ( III ) tetraphenylporphyrinate (magnetic moment: μ eff = 3.1 ± 0.2 μ B at 273 K). The Mn atom is in the centre of the slightly ruffled porphyrinato core. The Mn - C CN distance of 2.01(2)/2.02(2) Å and the Mn - N p distance, varying between 1.972(13) and 2.016(14) Å, are normal values. The Mn - C CN - N group is bent (171(2)/174(2) °). At low temperatures, a molecular electronic resonance Raman effect is detected at 198 and 344 cm−1. It is attributed to intraconfigurational transitions Γ 1g → Γ 4g and Γ 1g → Γ 3g Γ 5g , respectively, arising from the spin-orbit split 3 T 1g ground state of low-spin Mn ( III ), assuming pseudo-octahedral symmetry. Weak Q and intense B (Soret) transitions at 17 300 and 23 200 cm−1, respectively, as well as four weak trip–multiplet transitions are observed at 8650, 12 000, 14 900 and 19 900 cm−1.

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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

Zeitschrift für Naturforschung A ◽

10.1515/zna-1995-0915 ◽

1995 ◽

Vol 50 (9) ◽

pp. 881-887 ◽

Cited By ~ 3

Author(s):

Svend Sievertsen ◽

Lutz Galich ◽

Heiner Homborg

Keyword(s):

Phase Transition ◽

Raman Spectrum ◽

Raman Spectra ◽

Ground State ◽

Raman Effect ◽

Resonance Raman ◽

Spin Orbit ◽

Octahedral Symmetry ◽

Molecular Electronic ◽

Resonance Raman Spectra

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.

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