1507386-01-7Relevant academic research and scientific papers
Neutral, cationic, and anionic low-spin iron(III) complexes stabilized by amidophenolate and iminobenzosemiquinonate radical in N, N, O ligands
Rajput, Amit,Sharma, Anuj K.,Barman, Suman K.,Koley, Debasis,Steinert, Markus,Mukherjee, Rabindranath
, p. 36 - 48 (2014)
A brownish-black complex [FeIII(L)2] (1) (S = 0), supported by two tridentate redox-active azo-appended o-amidophenolates [H 2L = 2-(2-phenylazo)-anilino-4,6-di-tert-butylphenol], has been synthesized and structurally characterized. In CH2Cl2 1 displays two oxidative and two reductive 1e- redox processes at E1/2 values of 0.48 and 1.06 V and -0.42 and -1.48 V vs SCE, respectively. The one-electron oxidized form [1]+ isolated as a green solid [FeIII(L)2][BF4] (2) (S = 1/2) has been structurally characterized. Isolation of a dark ink-blue one-electron reduced form [1]- has also been achieved [CoIII(η5- C10H15)2][FeIII(L)2] (3) (S = 1/2). Moessbauer spectral parameters unequivocally establish that 1 is a low-spin (LS) FeIII complex. Careful analysis of Moessbauer spectral data of 2 and 3 at 200 and 80 K reveal that each complex has a major LS FeIII and a minor LS FeII component (redox isomers): [FeIII{(LISQ)-?}2]+ and [FeII{(LIBQ)0}{(LISQ) -?}]+ (2) and [FeIII{(LAP) 2-}2]- and [FeII{(L ISQ)-?}{(LAP)2-}]- (3). Notably, for both at 8 K mainly the major component exists. Broken-Symmetry (BS) Density Functional Theory (DFT) calculations at the B3LYP level reveals that in 1 the unpaired electron of LS FeIII is strongly antiferromagnetically coupled with a π-radical of o- iminobenzosemiquinonate(1-) (LISQ)-? form of the ligand, delocalized over two ligands providing 3- charge (X-ray structure). DFT calculations reveal that the unpaired electron in 2 is due to (L ISQ)-? [LS FeIII (SFe = 1/2) is strongly antiferromagnetically coupled to one of the (LISQ) -? radicals (Srad = 1/2)] and 3 is primarily a LS FeIII complex, supported by two o-amidophenolate(2-) ligands. Time-Dependent-DFT calculations shed light on the origin of UV-vis-NIR spectral absorptions for 1-3. The collective consideration of Moessbauer, variable-temperature (77-298 K) electron paramagnetic resonance (EPR), and absorption spectral behavior at 298 K, and DFT results reveals that in 2 and 3 the valence-tautomerism is operative in the temperature range 80-300 K.
