A new N6 hexadentate ligand and a novel heptacoordinated N6O-type Fe(III) compounds: Synthesis, characterization and structure of [Fe(dimpyen)(OH)](A)2 (A = PF6− or ClO4−)

In this contribution, we report the syntheses of a novel N6 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 N6O-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)](PF6)2 (1) and [Fe(dimpyen)(OH)](ClO4)2 (2) which both crystallize with an intermediate geometry, between pentagonal bipyramidal and monocapped octahedral. The UV–Vis spectra in CH3CN 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 (λmax 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 E1/2 = −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 O2(g) reaction.