Wydział Chemii

Krystyna Rachlewicz

Lechosław Latos-Grażyński

E. Vogel

Zbigniew Ciunik

Lucjan B. Jerzykiewicz

2002

Inorganic Chemistry

41

1979-1988

https://doi.org/10.1021/ic010725j

Naukowa

Angielski

Artykuł

Five-coordinate iron(III) 2,7,12,17-tetrapropylporphycene (TPrPc)Fe^IIIX (X = C₆H₅O^-, Cl^-, Br^-, I^-, ClO₄^-) complexes have been investigated. The ¹H NMR spectra demonstrate downfield shifts for pyrrole resonances [(TPrPc)Fe^III(C₆H₅O), 65.3 ppm; (TPrPc)Fe^IIICl, 28.5 ppm] but large upfield ones for (TPrPc)Fe^IIIBr (−7.8 ppm), (TPrPc)Fe^IIII (−49.4 ppm), and (TPrPc)Fe^IIIClO₄ (−77.1 ppm) (294 K, CD₂Cl₂). The pyrrole chemical shifts span the remarkable +70 to −80 ppm range. The variable-temperature ¹H NMR spectra of (TPrPc)Fe^IIIX demonstrate anti-Curie behavior with a sign reversal for (TPrPc)Fe^IIICl. These behaviors are consistent with the admixed S = 3/2, 5/2 ground electronic state with a dominating contribution of the S = 3/2 one. In terms of the chemical shift, (TPrPc)Fe^III(ClO₄) can be considered as an example of the purest S = 3/2 state in the investigated series. The extent of the S = 5/2 contribution in the admixed S = 3/2, 5/2 ground electronic state, as gradated solely the basis of the pyrrole proton paramagnetic shifts, is controlled by the strength of the axial ligand, following the magnetochemical series (Evans, D. R.; Reed, C. A. J. Am. Chem. Soc. 2000, 122, 4660). Significantly iron(III) 2,7,12,17-tetrapropylporphycene, soluble in typical organic solvents, can be considered as a universal framework to classify the ligand strength in a magnetochemical series, consistently using the β-H pyrrole paramagnetic shifts as a fundamental criterion. The structure of (TPrPc)Fe^IIICl has been determined by X-ray crystallography. The iron is five-coordinate with bonds of nearly equal length to the four pyrrole nitrogen atoms (Fe−N in the range 1.983(5)−2.006(6) Å). The iron lies 0.583(1) Å out of the mean plane of the macrocycle and 0.502(5) Å out of the mean N₄ plane. In the solid, pairs of molecules are positioned about the center of symmetry so there is face-to-face π−π contact. The mean plane separation is 3.38 Å, and the lateral shift of the porphycene center along the Fe−N bond is 4.490 Å. The distance from one porphycene center to the other is 5.62 Å, and the iron−iron separation is 6.304(2) Å.

https://doi.org/https://doi.org/10.1021/ic010725j

https://www.acs.org/content/acs/en.html