The complexation of iron(III) with (1,5)bis(2-hydroxybenzamido)3-azapentane (H 2 L) under varying [H + ] T (0.01-0.1 mol dm )3 ) and [Fe III ] T (3.0 · 10 )4 -1.7 · 10 )2 , ½L T ¼ ð0:5 À 1:0Þ Â 10 À4 mol dm )3 ) (I=0.3 mol dm )3 , 10% v/v, MeOH + H 2 O, 25.0°C) was reversible and displayed monophasic kinetics; the dominant path involved FeOH 2+ and H 3 L + . The mechanism is essentially a dissociative interchange (I d ) and dissociation of the aqua ligand from the encounter complex, [Fe(OH 2 ) 5 OH 2+ , H 3 L + ] is rate-limiting. Equilibrium measurements indicated that the ligand binds iron(III) in a bidentate, tetradentate and pentadentate fashion under varying pH conditions. Iron(III) promoted deprotonation of the phenol moieties, and sec-NH þ 2 of the dien unit are in tune with this proposition. The octahedral coordination of ½FeðHL=LÞðOH 2 Þ 2þ=þ is further supported by the aqua ligand substitution by AcO ) , NCS ) , N À 3 =N 3 H; SO 2À 3 =HSO À 3 . However, marked pK perturbation of the bound ascorbate in [Fe(L)(HAsc/Asc)] 0/) (DpK {[Fe(L)(HAsc)] ) HAsc)} =6) is compelling evidence for chelation of HAsc ) / Asc 2) leading to unusual hepta coordination of iron(III) in the ascorbate complexes. Despite the multidentate nature of the ligand, its iron(III) complexes remain sensitive to reduction by S IV and ascorbic acid.The complex (nitrato){(1,5)bis(2-hydroxybenzamido)3-azapentane}iron(III) has been synthesised and characterised by elemental analysis, i.r. and u.v.-vis spectral measurements. The room temperature magnetic moment (l eff =4.2 BM) conforms to the intermediate spin state of iron(III) (S=3/2) which is further supported by e.s.r. measurements (77 K, g=4.2, 8.1) and the 57 Fe Mo¨ssbauer spectrum (d=0.41 mm s )1 ; D E Q ¼ 0:78 mm/s). The cyclic voltametry (MeOH, TEAP as background electrolyte) display only one quasi-reversible peak in the )0.254 to )0.4 V range (vs. SCE), the irreversibility being due to the formation of an iron(II) complex which dissociates under the experimental conditions.

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The Mn IV complex of tetra-deprotonated 1,8-bis(2-hydroxybenzamide)-3,6-diazaoctane (Mn IV L) engrossed in phenolate-amido-amine coordination is reduced by HSO 3 À and SO 3 2À in the pH range 3.15-7.3 displaying biphasic kinetics, the Mn III L À being the reactive intermediate. The Mn III L À species has been characterized by u.v.-vis. spectra {k max , (, dm 3 mol À1 cm À1 ): 285 (15 570), 330 sh (7570), 469(6472), 520 sh (5665), pH ¼ 5.42}. SO 4 2À was the major oxidation product of S IV ; dithionate is also formed (18 ± 2% of [Mn IV ] T ) which suggests that dimerisation of SO 3 À• is competitive with its fast oxidation by Mn IV/III . The rates and activation parameters for Mn IV L + HSO 3 À (SO 3 2À) fi Mn III L À ; Mn III L À + HSO 3 À (SO 3 2À ) fi Mn II L 2À are reported at 28.5-45.0°C2À is ca. eight times faster than by HSO 3 À both for Mn IV L and Mn III L À . There was no evidence of HSO 3 À /SO 3 2À coordination to the Mn centre indicating an outer sphere (ET) mechanism which is further supported by an isokinetic relationship. The self exchange rate constant (k 22 ) for the redox couple, Mn III L À /Mn IV L (1.5 · 10 6 dm 3 mol À1 s À1 at 25°C) is reported.

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