Kinetics and mechanism of the reactions of hexaaqua rhodium (III) with sulphur (IV) in aqueous medium |
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| Authors: | Suprava Nayak and Anadi C. Dash |
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| Affiliation: | (1) Department of Chemistry, Utkal University, 751 004 Bhubaneswar, India |
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| Abstract: | ![]()
An O-bonded sulphito complex, Rh(OH2)5(OSO2H)2+, is reversibly formed in the stoppedflow time scale when Rh(OH2) 6 3+ and SO2/HSO 3 − buffer (1 2)5OH2++ SO2 □ Rh(OH2)5(OSO2H)2+ (k1/k-1), k1 = (2.2 ±0.2) × 103 dm3 mol−1 s−1, k−1 = 0.58 ±0.16 s−1 (25°C,I = 0.5 mol dm−3). The protonated O-sulphito complex is a moderate acid (K d = 3 × 10−4 mol dm−3, 25°C, I= 0.5 mol dm−3). This complex undergoes (O, O) chelation by the bound bisulphite withk= 1.4 × 10−3 s−1 (31°C) to Rh(OH2)4(O2SO)+ and the chelated sulphito complex takes up another HSO 3 − in a fast equilibrium step to yield Rh(OH2)3(O2SO)(OSO2H) which further undergoes intramolecular ligand isomerisation to the S-bonded sulphito complex: Rh(OH2)3(O2SO)(OSO2)- → Rh(OH2)3(O2SO)(SO3)− (k iso = 3 × 10−4 s−1, 31°C). A dinuclear (μ-O, O) sulphite-bridged complex, Na4[Rh2(μ-OH)2(OH)2(μ-OS(O)O)(O2SO)(SO3) (OH2)]5H2O with (O, O) chelated and S-bonded sulphites has been isolated and characterized. This complex is sparingly soluble in water and most organic solvents and very stable to acid-catalysed decomposition |
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| Keywords: | Rhodium-sulphur complexes intramolecular ligand isomerisation sulphite-bridged complexes |
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