RESUMO
The intramolecular magnetic interactions in one-electron oxidized iron(iii) porphyrin π-radical cations, [Fe(OETPPË)Cl][SbCl6] (1), [Fe(OMTPPË)Cl][SbCl6] (2) and [Fe(TPPË)Cl][SbCl6] (3), have been compared by means of X-ray crystallography, SQUID magnetometry, cyclic voltammetry, UV-Vis spectroelectrochemical analysis, NMR spectroscopy analysis and unrestricted DFT calculations. Unlike a generally recognized antiferromagnetic coupling dxy↑dxz↑dyz↑dz2↑dx2-y2↑PË+(a2u)↓ (S = 2) state via a weak bonding interaction as in (3), we have disclosed that a strong bonding interaction among iron dx2-y2 and porphyrin a2u orbitals forms in (1) into a highly delocalized Ψπ = [PË+(a2u) + FeIII(dx2-y2, dz2)] orbital that is able to accommodate two spin-paired electrons to form the Ψπ2dxy1dxz1dyz1, dz21 (S = 2) ground state. Concurrently, the spin polarization effect is exerted on the paired spins in the Ψπ orbital by magnetic induction from the remaining unpaired electrons in the iron d orbitals. The interpretation mentioned above is further verified by the diamagnetic nature of the saddled copper(ii) porphyrin π-cation radical, CuII(OETPPË)(ClO4) (S = 0), where the strong bonding interaction leads to the Ψπ2dxy2dxz2dyz2dz22 (S = 0) ground state but no spin polarization exists. Thus, the magnetic nature of the iron(iii) porphyrin π-radical cation is tuneable by saddling the ring planarity.
RESUMO
Ni(III)(OETPPË)(Br)2 is the first Ni(III) porphyrin radical cation with structural and (1)H and (13)C paramagnetic NMR data for porphyrinate systems. Associating EPR and NMR analyses with DFT calculations as a new model is capable of clearly determining the dominant state from two controversial spin distributions in the ring to be the Ni(III) LS coupled with an a1u spin-up radical.
Assuntos
Metaloporfirinas/química , Níquel/química , Isótopos de Carbono , Cátions/síntese química , Cátions/química , Radicais Livres/síntese química , Radicais Livres/química , Espectroscopia de Ressonância Magnética , Metaloporfirinas/síntese química , Modelos Moleculares , Prótons , Teoria QuânticaRESUMO
Saddle-shaped Co(II)[OET(p-R)PP] (R = CF3, H, CH3) can be readily oxidized with Cl2, Br2, and I2 to the corresponding one-electron-oxidation product Co[OET(p-R)PP]X (X = Cl, Br, I) with the clear character of a ring cation radical. With the series of (1)H and (13)C NMR spectra of these related complexes, both the axial ligand and peripheral substituent of the ring macrocycle are proven to act as a dual channel to tune spin coupling between low-spin Co(II) and a porphyrin π-cation radical. Density functional theory calculations have shown that the antiferromagnetic coupling between spins residing in d(z)(2) and a(2u) are expected to exist as the ground state. The paramagnetic properties are attributed to an a(1u)-type ferromagnetic excited triplet state.
Assuntos
Cobalto/química , Porfirinas/química , Marcadores de Spin , Espectroscopia de Ressonância Magnética Nuclear de Carbono-13 , ElétronsRESUMO
Electrochemical properties of substituted free base meso-tetraphenylporphyrins (H(2)T(o,o'-X)PP, H(2)T(o-X)PP, and H(2)T(p-X)PP, where X = OCH(3), CH(3), H, F, or Cl on the phenyl rings) are examined by cyclic voltammetry. When a substituent is located only at the para position of the meso-phenyl group, the difference between the first and second oxidation potentials (ΔE(ox), i.e., E(2)(ox) - E(1)(ox)), is generally significantly smaller than those of the H(2)TPPs with bulky o,o'-substituents on the phenyl group. This trend is elucidated with density functional theory calculations and attributed mainly to the sterically controlled π-conjugation of the meso-phenyl groups to the central porphyrin ring, rather than the often discussed deformation of porphyrin.
RESUMO
Through density functional calculation and NMR spectroscopy, an unexpected bonding interaction between d(xy) and axial cyanides is revealed to account for the lower shielding of axial cyanide of ruffled [Fe(TRP)(CN)(2)](-) complexes with the contribution of the unusual low-spin electronic structure (d(xz)d(yz))(4)(d(xy))(1).
RESUMO
An unusual intermediate-spin electronic structure d(xz,yz)(3)d(xy)(1)d(z(2))(1) has been assigned to the six-coordinate saddled [Fe(OETPP)(4-CNPy)(2)](+) complex through density functional calculation and NMR spectroscopy analysis.
Assuntos
Compostos Férricos/química , Porfirinas/química , Modelos Moleculares , Estrutura MolecularRESUMO
Confluence of NMR for paramagnetic molecules and the complementary density functional theory calculations reveals an anomalous spin-polarization mechanism that is maximized in high-spin d(4) complexes. It is critical to realize this mechanism to correctly rationalize the spin-density distribution around the porphyrin macrocycle.
RESUMO
Through density functional calculation and NMR spectroscopy, an unusual intermediate-spin electronic structure (d(xz)d(yz))3(d(xy))1(d(z)2)1 has been assigned to the six-coordinate saddled [Fe(OETPP)(THF)2]+ complex instead of the corresponding ruffled [Fe(TiPrP)(THF)2]+ complex.
RESUMO
Bonding interactions between the iron and the porphyrin macrocycle of five- and six-coordinate high-spin iron(III)-porphyrin complexes are analyzed within the framework of approximate density functional theory with the use of the quantitative energy decomposition scheme in combination with removal of the vacant pi orbitals of the porphyrin from the valence space. Although the relative extent of the iron-porphyrin interactions can be evaluated qualitatively through the spin population and orbital contribution analyses, the bond strengths corresponding to different symmetry representations can be only approximated quantitatively by the orbital interaction energies. In contrast to previous suggestions, there are only limited Fe --> P pi back-bonding interactions in high-spin iron(III)-porphyrin complexes. It is the symmetry-allowed bonding interaction between d(z)2 and a(2u) orbitals that is responsible for the positive pi spin densities at the meso-carbons of five-coordinate iron(III)-porphyrin complexes. Both five- and six-coordinate complexes show significant P --> Fe pi donation, which is further enhanced by the movement of the metal toward the in-plane position for six-coordinate complexes. These bonding characteristics correlate very well with the NMR data reported experimentally. The extraordinary bonding interaction between d(z)2 and a(2u) orbitals in five-coordinate iron(III)-porphyrin complexes offers a novel symmetry-controlled mechanism for spin transfer between the axial ligand sigma system and the porphyrin pi system and may be critical to the electron transfer pathways mediated by hemoproteins.