UNSPECIFIED. (1993) SYNTHESIS AND PROPERTIES OF THE IRON(II) COMPLEX OF A PENTADENTATE LIGAND DERIVED FROM DIAZAOXACYCLONONANE. INORGANIC CHEMISTRY, 32 (3). pp. 297-302. ISSN 0020-1669

Abstract

The pentadentate ligand DPC (DPC = 4,7-bis(2-picolyl)-4,7-diaza-1-oxacyclononane) reacts with FeCl2 in MeOH to produce the high-spin (S = 2) iron(II) complex (lambda(max) = 260 and 378 nm in water). The structure of the complex was determined by X-ray crystallography. Crystal data: orthorhombic space group P2(1)2(1)2(1), a = 8.016 (3) angstrom, b = 13.188 (8) angstrom, c = 20.539 angstrom, U = 2171.3 angstrom3, Z = 4, D(c) = 1.69 cm-3, Mo Kalpha radiation, lambda = 0.710 69 angstrom, mu(Mo Kalpha) = 0.96 mm-1, T = 290 K, and R = 0.049 for 1895 unique observed (I/sigma(I) greater-than-or-equal-to 2.0) reflections. Cyclic voltammetry and chronoamperometry in MeCN revealed that the complex undergoes a reversible one electron redox process at E1/2 = 0.71 V vs NHE (D = 7.6 X 10(-6) cm2/s). Moreover, ESR spectral studies identified the in situ electrochemically generated Fe(III) species as a high-spin complex, and electrochemical studies indicate 6-coordination for both the iron(II) and iron(III) species. In aqueous solution, for pH > 9, Fe(DPC)3+ forms a hydroxo complex, as a result of which the iron(III/II) redox couple is shifted negative to 0.54 V vs NHE (pH = 9.6). Spectroelectrochemical measurements with a long optical path thin-layer cell containing parallel glassy-carbon working electrodes showed that, during the oxidation of Fe(DPC)2+ in 2 M aqueous KCl, the MLCT absorption band at 378 nm disappears, with a concomitant increase in absorbance with lambda(max) = 310 nm, corresponding to the formation of [Fe(DpC)Cl]2+.

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