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Title: Reactions of β-cis-(diaqua)(triethylenetetramine)cobalt(III) with sulphur(IV) in aqueous medium: A thermal and photochemical study
Authors: Dash, Anadi C
Jena, Kishore C
Das, Arabinda
Issue Date: Jul-1999
Publisher: NISCAIR-CSIR, India
Abstract: The initial fast reaction of SO2 with β-[Co(trien) (OH)(OH2)]2+ yields the O-bonded sulphito complex, β -[Co(trien) (OH2) (OSO2-O)] + for which kf= (4.76 ± 0.25) x 107 dm3 mol-1 s-1, ∆H = 42.1 ± 5.1 kJ mol-1, ∆S = 43 ± 17 J K-1 mol-1 at 25°C and I = 1.0 mol dm-3 . The O-sulphito complex undergoes H+ -catalysed aquation with k = (1.1 ± 0.2) x 106 dm3 mol -1s-1 (25°C,I = 1.0 mol dm-3). These data are consistent with the rate limiting addition of SO2 to CoIII-OH and breakage of S-O bond in the formation and aquation of the O-sulphito complex respectively. The O-sulphito complex undergoes intramolecular electron transfer and ligand linkage isomerisation. Co-OSO2+→ Co-SO3+ for which kred(30°C) = (0.28 ± 0.03) x 10-4 S-1, ∆H = 76 ± 12 kJ mol-1, ∆S = -81 ± 39 J K-1mol-1 and kiso(30°C) = (0.44 ± 0.12) x 10-4 s-1, ∆H = 57 ± 7 kJ mol-1, ∆S = -138 ± 24 J K-1mol-1I respectively. The β -cis-[Co(trien)(OH2)(SO3-S)] + has been isolated in the solid state and characterised. It does not show exceptional lability of the aqua ligand for substitution and is substantially stable to intramolecular electron transfer between COIII and SIV under thermal condition. The conventional flash photolysis of this S-bonded sulphito complex has been shown to generate the corresponding O-sulphito complex as a transient while its steady state photolysis (254 nm) resulted in photo reduction without significant build up of any intermediate.
Page(s): 660-669
Appears in Collections:IJC-A Vol.38A(07) [July 1999]

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