A new N_6 hexadentate ligand and a novel heptacoordinated N _6O-type Fe(III) compounds: Synthesis, characterization and structure of [Fe(dimpyen)(OH)](A)_2 (A = PF_6~- or ClO _4~-)

摘要

In this contribution, we report the syntheses of a novel N_6 donor set ligand, dimpyen = N1,N2-di[(1-methyl-1H-2-imidazolyl) methyl]-N1,N2-di(2-pyridilmethyl)-1,2-ethanediamine. This type of ligand was designed to modulate the properties of the metal ions bound to it. The reaction with Fe(II) gives off a new heptacoordinated iron(III) complex. We study the spectroscopic (UV-Vis), magnetic and electrochemical behavior and also made the structural determination with X-ray diffraction at 134 K and a heptacoordinated N_6O-type derivative of Fe(III) is reported as well. This complex crystallize as perchlorate or hexafluorophosphate and the formula of these derivatives are [Fe(dimpyen)(OH)](PF_6)_2 (1) and [Fe(dimpyen)(OH)](ClO_4)_2 (2) which both crystallize with an intermediate geometry, between pentagonal bipyramidal and monocapped octahedral. The UV-Vis spectra in CH_3CN solution show a shoulder at 306 nm assigned to one ligand-metal charge-transfer (LMCT) transition, in addition, a weaker and wide band assigned to the charge transfer HO-Fe transition (λ_(max) at 404 nm with an extinction coefficient of 818 cm~(-1) M~(-1)) is also observed. The magnetic studies corroborate a high-spin iron (III) species in all the temperature range considered. Measurements of cyclic voltammetric confirm a reversible system Fe(III) species, with E_(1/2) = -0.380 V/Fc~+-Fc, this low potential value explains the high stability of the Fe(III) and the easy oxidation of Fe(II) by atmospheric O_2(g) reaction.