Carbon-13 NMR Spectroscopy, Electron Spin Distribution, and Valence State of Pentacoordinate Manganese Tetraphenylporphyrin Complexes

Abstract

The solution optical and NMR spectra of (TPP)MnX (X = F-, NCO, CH3CO2", HCO2", N3", Cl", Br, NO2", NO3", NCS", CN-, I", C104", BF4", B(C6H5)4-) indicate that ionic bonding may be particularly important in manganese tetraphenylporphyrin complexes. A Karplus-Fraenkel equation utilization of 13C NMR spectra for the calculation of electron spin densities at the porphyrin nuclei uncovers an unexpectedly high positive density at the pyrrole -carbon sites. The densities for the acetato, nitrato, and perchlorate complexes are 0.049, 0.056, and 0.063, respectively. Such high densities are unlikely to be covalent in origin, and accordingly an axial ligand dependent mixture of the [Mnn(S = 3/2,4A2)P(S = *l/2,2 2)•"]+ + [Mnm(S = 2,5Ai)P2"]+ electronic states is proposed for the ground valence state of manganese tetraphenylporphyrin complexes. The calculations probably underestimate the -carbon spin densities, so the C2v (d^,^)0 (d^)1 (dxz dyz)2 (dxy)2 (a2(vr))1 (3 ( ))2 [MnnP,-]+ valence state is likely to be the principal ground-state contributor. The electron spin at the -carbon sites dominates the carbon-13 spectroscopy through polarization and correlation. In contrast to previous deductions of negative ( ) density, but in accord with the hyperporphyrin optical spectra, a high positive ( ) density is present at the meso sites. This spin density is effectively undermined by the greater spin at the -carbon location. The phenyl residue NMR reflects an axial ligand dependent balance of spin polarization and positive spin delocalization from the meso position. The

Electrochemistry and Spectroscopy of Sulfate Complexes of (Tetraphenylporphyrinato)manganese

“…1), in close agreement with the reported spectrum [2]. By comparison, the spectrum of [Mn(tpp)Cl] in CHCl 3 exhibited absorbances similar to the literature values [13], with a Soret band at 479 nm and other VIS bands at 528, 583, and 618 nm. The spectral features observed for both [Mn 2 (tpp) 2 CHCl 3 , addition of excess sulfate shifted the Soret band from 466 to 469 nm ( Fig.…”

“…b) The VIS spectrum observed for the reaction product was different from that observed for [Mn 2 (tpp) 2 (SO 4 )] and [Mn(tpp)Cl], and the reported spectrum of [Mn(tpp)(HSO 4 )] [2]. c) The VIS spectrum and the e III /e IV ratio of the product were similar to those reported for other monomeric [Mn(tpp)X] complexes containing −hard× axial ligands [13]. Additionally, the e III /e IV and e IV /e V ratios calculated for the product were different from those observed for the parent dimer and the reported spectrum of [Mn(tpp)(HSO 4 [5].…”

“…Additionally, the e III /e IV and e IV /e V ratios calculated for the product were different from those observed for the parent dimer and the reported spectrum of [Mn(tpp)(HSO 4 [5]. This may indicate a significantly greater degree of ionic bonding between the axial sulfato ligand and porphyrinatomanganese complexes compared to their iron counterparts [11] [13]. As with the porphyrinatoiron complexes [5], the sulfate ion forms a stronger complex with the porphyrinatomanganese adduct in non-coordinating solvents than in coordinating solvents, where the dimer exists primarily as a bissolvent-coordinated complex in the absence of excess sulfate.…”

Electrochemical and binding properties of a meso-tetra(4-pyridyl)porphyrinatozinc supermolecule containing four μ3-oxo-triruthenium acetate clusters

“…The 1 H and 13 C NMR spectra of ZnTCP in CD 3 CN were assigned based on the COSY, DEPT-135 and HETCOR experiments and confirmed by comparison with the spectra of analogous free base [19] species (H 2 TCP) as well as [Ru 3 O(CH 3 COO) 6 L 3 ] complexes [24,[33][34][35] and other meso-substituted porphyrins [18,36,37]. The 1 H NMR and homonuclear bidimensional COSY spectra of a 2 Â 10 À3 mol dm À3 CD 3 CN solution of ZnTCP are shown in Fig.…”

A New Route towards Redox Bistability through the Inspection of Manganese–Porphyrin Complexes

“…Even though iron-porphyrins have been by far the most extensively studied class of porphyrin derivatives, the interest in manganese-porphyrins and group 15-element porphyrins (e.g., Sb III and P V ) has grown with the possibility to fabricate NMR spectroscopic image-enhancement agents, nonlinear optical materials, [1] and photochemical oxygenating reagents. [2,3] Moreover, molecular-based devices are also considered to be promising targets for information storage.…”