Formation of pure intermediate spin complexes in highly nonplanar iron(iii) porphyrins

Recent developments in the 13 C NMR spectroscopic analysis of paramagnetic hemes and heme proteins

“…Ferrihemes possessing the S=/2, (d xy ) 2 (d xz , d yz ) 2 (d z 2 ) 1 spin state have been shown to exhibit complicated distortions from planarity [85,98,99], which suggests they might exist in solution as a complex mixture of interconverting conformers with similar energies. Nonplanar hexacoordinated ferrihemes possessing a pure S=3/2 spin state also exhibit a unique pattern of 13 C NMR shifts [86] with very large downfield β shifts (≈1,000 ppm), large downfield C α shifts (≈600 ppm), and large upfield C m shifts (≈-300 ppm) (Fig.…”

Spin–spin interactions in iron(III) porphyrin radical cations with ruffled and saddled structure

“…However, there is no example of the iron(III) radical cation where the iron(III) ion adopts a pure intermediate-spin state. We and others have reported that the deformation of porphyrin ring stabilizes the intermediate-spin state [14][15][16][17][18][19][20]. In fact, ruffled or saddled complexes carrying weak axial ligands such as Fe(T i PrP)ClO 4 and Fe(OETPP)ClO 4 exhibit an essentially pure intermediate-spin state [21,22].…”

Factors that stabilize the (dxz,dyz)Ikezaki1, Ohgo2, Watanabe3 et al. 2008Inorganic Chemistry CommunicationsSelf Cite5020View full textAdd to dashboardCite

“…of benzaldehyde. Table 1 lists the 1 H NMR chemical shifts and isotropic shifts of 5 [21,22], together with those of 1-4 reported in our previous paper [7,8,11,20]. NMR data of [Fe(T i PrP)(4-MePyNO) 2 ] + (6) are also listed in Table 1 as a typical example adopting mainly the S = 5/2 spin state with a minor contribution of the S = 3/2 [20].…”

“…They are: (i) axial ligands with oxygen as coordinating atom, (ii) highly ruffled porphyrin core, (iii) axial ligands with multiple bond. Factor (i) is necessary to obtain an essentially pure intermediate-spin state [11][12][13]18]. Factor (ii) is necessary for the d xy -a 2u interaction, which destabilizes the d xy orbital relative to the d p orbitals [4,7,8].…”

“…Recent studies have shown, however, that several complexes with weak axial ligands and/or highly deformed porphyrin core adopt an essentially pure S = 3/2 spin state [10][11][12][13][14][15][16][17]. Similar to the low-spin complexes, there should be at least two electronic ground states, ðd xy Þ 2 ðd xz ; d yz Þ 2 ðd z 2 Þ 1 and ðd xz ; d yz Þ 3 ðd xy Þ 1 ðd z 2 Þ 1 , even in the intermediate-spin (S = 3/2) complexes as shown in Scheme 1b; they are signified as the S = 3/2(d p ) and S = 3/2(d xy ), respectively.…”