One-electron oxidized nickel(II) complexes of bis and tetra(salicylidene) phenylenediamine Schiff bases: from monoradical to interacting Ni(III) ions.

The Ni(II) complexes of the mono and di-nucleating Schiff base ligands H2LOMe (bis(3,5-di-tert-butylsalicylidene)-4,5-dimethoxy-o-phenylenediamine), H2LNO2 (bis(3,5-di-tert-butylsalicylidene)-4,5-dinitro-o-phenylenediamine) and H4Lbis (tetrakis(3,5-dimethoxy-o-phenylenediamine)-1,2,4,5-benzenetetraamine) were synthesized and characterized. H2LOMe and H2LNO2 differ from one another by the substituents of the phenylene spacer, electron-donating methoxy or electron-withdrawing nitro groups, resp. X-ray crystal structure anal. shows that the Ni(II) ion(s) resides within a square planar geometry in each complex. Cyclic voltammetry curves reveal that the electrochem. communication is strongly influenced by the substituent and the solvent. The 1-electron oxidized species [Ni(LOMe)]+ in CH2Cl2 is a phenoxyl radical with partial delocalization of the spin d. on a metal orbital (contribution of 6.8{%}), whereas [Ni(LNO2)]+ disproportionates once it is generated. A shift of electronic hole is obsd. in the presence of pyridine: both [Ni(LOMe)]+ and the 1-electron oxidn. product of [Ni(LNO2)] are converted into mononuclear octahedral Ni(III) complexes involving two axially bound pyridines. In the dinickel(II) complex of H4Lbis, [Ni2(Lbis)], the phenylene spacer mediates an electronic communication between the two metallic sites. Single oxidn. of [Ni2(Lbis)] affords the delocalized phenoxyl radical [Ni2(Lbis)]+, whose EPR signature is close to that of [Ni(LOMe)]+. Double oxidn. affords the bis-{\{}NiII-delocalized radical{\}} species [Ni2(Lbis)]2+. Each radical is located at a distinct metallic site and a weak but appreciable magnetic interaction exists between the paramagnetic centers. In the presence of pyridine, a complex involving two ferromagnetically coupled Ni(III) ions was obtained. The magnetic coupling was estd. to 3.7 cm-1, while the zero field splitting parameters are |D| = 0.012 cm-1 and E = 0. They are weak, in agreement with the large intermetallic distance (7.7 {\AA}) obsd. in the neutral precursor [Ni2(Lbis)]. [on SciFinder(R)]


Soumis le 12 avril 2018