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Three six-coordinate cobalt(III) complexes containing electron-rich phenolato pentadentate [N2O5] ligands were synthesized and characterized, namely, [CoIII(L1)(MeOH)] ( 1), [CoIII(L2)(MeOH)] ( 2) and [CoIII(L3)(MeOH)] ( 3), where L1, L2 and L3 are the triply deprotonated, triply negative form of( E)-6,6′-[({2-[(3,5-di- tert-butyl-2-hydroxybenzylidene)amino]phenyl}azanediyl)bis(methylene)]bis(2,4-di- tert-butylphenol), ( E)-6,6′-[({3-[(3,5-di- tert-butyl-2-hydroxybenzylidene)amino]naphthalen-2-yl}azanediyl)bis(methylene)]bis(2,4-di- tert-butylphenol) and ( E)-6,6′-[({2-[(2-hydroxy-3-methoxybenzylidene)amino]phenyl}azanediyl)bis(methylene)]bis(2,4-di- tert-butylphenol), respectively. Crystal structures were obtained for 1- 3 and reveal a hexacoordinate cobalt(III) ion bound to the [N2O3] donors of each ligand and a methanol molecule occupying the sixth position. The complexes exhibited comparable electronic behavior dominated by phenolate→cobalt charge transfer processes and four redox-accessible states involving three distinct phenolato/phenoxyl radical couples and a fourth process associated with the CoII/CoIII couple. The redox processes were cycled 30 times without major decomposition at the surface of the electrode for 1 and 2, indicating that the oxidized species should be substitutionally inert and do not degrade significantly upon cycling. Electronic-structure DFT calculations on models 1′ and 2′ favor the generation of localized phenoxyl radicals and suggest distinctive oxidation sequences associated to the nature of the ligands. [ABSTRACT FROM AUTHOR]

Two iron(III)-containing amphiphiles 1 and 2 have been synthesized with the [NN′O] ligands HLtBu-ODA (2-((octadecyl(pyridin-2-ylmethyl)amino)methyl)-4,6-di-tert-butylphenol) and HLI-ODA (2-((octadecyl(pyridin-2-ylmethyl)amino)methyl)-4,6-diiodophenol), respectively. Compound 1 is monometallic, whereas EXAFS data suggest that 2 is a mixture of mono- and bimetallic species. The archetypical [FeIII(LNN′O)2]+ complexes 3-9 have been isolated and characterized in order to understand the geometric, electronic, and redox properties of the amphiphiles. Preference for a monometallic or bimetallic nuclearity is dependent on (i) the nature of the solvent used for synthesis and (ii) the type of the substituent in the phenol moiety. In methanol, the tert-butyl-, methoxy-, and chloro-substituted 3, 4, and 5 are monometallic species, whereas the bromo- and iodo-substituted 6 and 7 form bimetallic complexes taking advantage of stabilizing methoxo bridges generated by solvent deprotonation. In dichloromethane, the bromo- and iodo-substituted 8 and 9 are monometallic species; however, these species favor meridional coordination in opposition to the facial coordination observed for the tert-butyl- and methoxy-substituted compounds. Molecular structures for species 5, 7, 8, and 9 have been solved by X-ray diffraction. Furthermore, the electronic spectrum of the amphiphile 1 was expected to be similar to those of facial/cis archetypes with similar substituents, but close resemblance was observed with the profile for those meridional/cis species, suggesting a similar coordination mode. This trend is discussed based on DFT calculations, where preference for the meridional/cis coordination mode appears related to the presence of tertiary amine nitrogen on the ligand, as when a long alkyl chain is attached to the [NN′O] headgroup. [ABSTRACT FROM AUTHOR]

Hydrolysis of the asymmetric pyridine- and phenol-containing ligand HL¹ (2-hydroxy-4-6-di-tert-butylbenzyl-2-pyridylmethyl)imine) led to the use of bis-(3,5-di-tert-butyl-2-phenolato-benzaldehyde)copper(II), [CuII(LSAL)2] (1) as a precursor for bis-(2,4-di-tert-butyl-6-octadecyliminomethyl-phenolato)copper(II), [CuII(L²)2] (3), bis-(2,4-di-tert-butyl- 6-octadecyl aminomethyl-phenolato)copper(II), [CuII(L2A)2] (3′), and bis-(2,4-di-tert-butyl-6-[(3,4,5-tris-dodecyloxy-phenylimino)-methyl]-phenolato)copper(II), [CuIIL³)2] (4). These complexes exhibit hydrophilic copper-containing head groups, hydrophobic alkyl and alkoxo tails, and present potential as precursors for redox-responsive Langmuir-Blodgett films. All systems were characterized by means of elemental, spectrometric, spectroscopic, and electrochemical techniques, and their amphiphilic properties were probed by means of compression isotherms and Brewster angle microscopy. Good redox activity was observed for 3 with two phenoxyl radical processes between 0,5 and 0.8 V vs Fc+/Fc, but this complex lacks amphiphilic behavior. To attain good balance between redox response and amphiphilicity, increased core flexibility in 3′ and incorporation of alkoxy chains in 4 were attempted. Film formation with collapse at 14 mN · m-1 was observed for the alkoxy-derivative but redox-response was seriously compromised. Core flexibility improved Langmuir film formation with a higher formal collapse and showed excellent cyclability of the ligand-based processes. [ABSTRACT FROM AUTHOR]