Aerobic FeIII–FeII Reduction in the Presence of 2,4,6‐Tri(2‐pyridyl)‐1,3,5‐triazine and Benzilic Acid: Synthesis and Characterization of a Heptacoordinate FeII–Nitrato Complex

Abstract

AbstractThe simultaneous presence of benzilic acid [Ph2C(OH)CO2H] and tptz [2,4,6‐tri(2‐pyridyl)‐1,3,5‐triazine] in FeIII‐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 FeII–nitrato complex, [FeII(tptz)(NO3)(MeOH)2](NO3) (1), along with a FeIII complex (2). In the presence of perchlorate ions in the reaction mixture, the quantitative reduction of FeIII leads to the isolation of a hexacoordinate FeII complex, [FeII(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 FeII in 1. On the basis of analytical, spectroscopic (IR, Mössbauer) and magnetic susceptibility data from polycrystalline samples of 2, an oxido‐bridged diferric structure is proposed [ΔEQ(78 K) = 1.79 mm s–1, JFe–Fe = –117 cm–1]. The Mössbauer spectra of the polycrystalline samples of 1 and 3 are consistent with high‐spin and low‐spin FeII, respectively, in anN/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).(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)