Département de chimie moléculaire

FeIII complexes of the sym. (H2L1) (2S,2'S)-[N,N'-bis(1-(2-hydroxy-3,5-di-tert-butylphenylmethyl))]-2,2'-bipyrrolidine and dissym. (2S,2'S)-[N,N'-(1-(2-hydroxy-3,5-di-tert-butylphenylmethyl))-2-(pyridylmethyl)]-2,2'-bipyrrolidine (HL2) ligands incorporating the bipyrrolidine backbone were prepd., and the electronic structure of the neutral and 1-electron oxidized species was studied. Cyclic voltammograms (CV) of FeL1Cl and FeL2Cl2 showed expected redox waves corresponding to the oxidn. of phenoxide moieties to phenoxyl radicals, which was achieved by treating the complexes with 1 equiv of a suitable chem. oxidant. The clean conversion of the neutral complexes to their oxidized forms was monitored by UV-visible-NIR spectroscopy, where an intense $π$-$π$* transition characteristic of a phenoxyl radical emerged [FeL1Cl]+.bul.: 25,500 cm-1 (9000 M-1 cm-1); [FeL2Cl2]+.bul.: 24,100 cm-1 (8300 M-1 cm-1). The resonance Raman (rR) spectra of [FeL1Cl]+.bul. and [FeL2Cl2]+.bul. displayed the characteristic phenoxyl radical $ν$7a band at 1501 and 1504 cm-1, resp., confirming ligand-based oxidn. EPR spectroscopy exhibited a typical high spin FeIII (S = 5/2) signal for the neutral complexes in perpendicular mode. Upon oxidn., a signal at g ≈ 9 was obsd. in parallel mode, suggesting the formation of a spin integer system arising from magnetic interactions between the high spin FeIII center and the phenoxyl radical. D. functional theory (DFT) calcns. further supports this formulation, where weak antiferromagnetic coupling was predicted for both [FeL1Cl]+.bul. and [FeL2Cl2]+.bul.. [on SciFinder(R)]