Aerobic Fe-III-Fe-II Reduction in the Presence of 2,4,6-Tri(2-pyridyl)-1,3,5-triazine and Benzilic Acid: Synthesis and Characterization of a Heptacoordinate Fe-II-Nitrato Complex

摘要

The simultaneous presence of benzilic acid [Ph2C(OH)CO2H] and tptz [2,4,6-tri(2-pyridyl)-1,3,5-triazine] in Fe-III-containing reaction mixtures leads to partial and/or quantitative metal reduction. In the presence of the oxidative NO3- ions in the reaction mixture, partial reduction of the metal leads to the isolation of a heptacoordinate Fe-II-nitrato complex, [Fe-II(tptz)-(NO3)(MeOH)(2)](NO3) (1), along with a Fe-III complex (2). In the presence of perchlorate ions in the reaction mixture, the quantitative reduction of Fe-III leads to the isolation of a hexa-coordinate Fe-II complex, [Fe-II(tptzH)(2)](ClO4)(4) (3). Complexes 1 and 3 have been structurally characterized and possess a pentagonal-bipyramidal and a distorted octahedral coordination geometry, respectively. In both complexes, tptz behaves as a tridentate ligand, adopting the terpy-like coordination mode, and is coordinated through the triazine nitrogen atom and the two adjacent pyridine nitrogen atoms. One asymmetrically coordinated chelate, NO3-, and two MeOH molecules complete the pentagonal-bipyramidal geometry around Fe-II in 1. On the basis of analytical, spectroscopic (IR, Mossbauer) and magnetic susceptibility data from polycrystalline samples of 2, an oxido-bridged diferric structure is proposed [Delta E-Q(78 K) = 1.79 mm s(-1), J(Fe-Fe) = -117 cm(-1)]. The Mossbauer spectra of the polycrystalline samples of 1 and 3 are consistent with high-spin and low-spin Fe-II, respectively, in an N/O coordination environment. Variable-temperature and variable-field magnetic measurements of 1 suggest significant zero-field splitting of the ferrous ions (D = 5.5 cm(-1)). ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)